daniel.haxx.se Today

A curl mountain movie

One of my favorite visuals for known vulnerabilities in curl is the mountain . It shows how many currently known vulnerabilities were present in the code through-out curl’s history. In the end of June 2026 it looks like this: Over time we get more vulnerabilities reported. Since every flaw has a version range during which the problem existed and with more issues that have overlapping version ranges, the mountain grows. It changes shape every time we do a release or we publish a new vulnerability. At this moment in time, curl version 7.34.0 is the release that contains the most number of known vulnerabilities: 101 . The worst one ever if you will. Out of a total of 206. The mountain uses different colors for different severity levels of the published vulnerabilities, as the legend in the top-left of the image explains. To illustrate the ever-changing nature of the shape and size, I wrote a script that renders the mountain the way it looked at specific dates in the past up until today. More specifically, the script renders one image for every month since curl started (March 1998). I then turned these 340 individual images into a little movie that shows how it grew into today’s shape. At four months/second. The data for this come from vuln.pm and the curl git repository . The graph rendering is based on the dashboard scripts . All images put into a movie with ffmpeg of course. Several people have asked what happened in 2016 that caused the notable drop. A slope if you will. If we zoom in on that, we can spot that curl 7.51.0 has eleven fewer vulnerabilities than the version before that. This release was the first one after the 2016 Cure53 code audit , but other than that there is no clear distinct process or obvious code changes that explain this trend shift. Lots of other graphs show just the ordinary pace and growth in various project areas. It was still fairly early days CI-wise but had been running at least a few CI jobs per commit for a few years already by then. curl was adopted into the OSS-Fuzz project in July 2017, which since then makes us find some issues better, but the drop looks like it happened before then. We had already been analyzing the code regularly on Coverity since a few years. Better tooling? New compiler options? We simply don’t know. As we keep announcing more vulnerabilities going forward, things will continue to change. Maybe I will come back and make another movie in five years?

Open Source Security Data Visualization

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daniel.haxx.se Yesterday

Trailing dots are the worst

Trailing dots after hostnames in URLs remain my worst enemies. I wrote about several problems with them in the past that involved those nasty things. They are still painful. When we shipped curl 8.21.0 on June 24 2026 we fixed at least three brand new problems that involved trailing dots. C’mon, follow me down the trailing dot rabbit hole, episode two. I can just feel that there will be a third episode as well in a future… Let’s for a second imagine that you create a URL that uses a numerical IPv4 address. Not entirely uncommon. For example lots of people use 127.0.0.1 in local tests etc. Used everywhere since the dawn of time. Now imagine that you add a trailing dot to this hostname, like “192.168.0.1.”. What does the trailing dot even mean here? This particular trailing dot caused a problem in curl. To figure out if curl should allow wildcard certificates when connecting to a TLS server, it needs to know if the given hostname is a numerical IP or a hostname. The check uses on the provided hostname extracted from the URL – which incidentally returns false for an IPv4 address that ends with dot! So if it isn’t a numerical address it is a hostname and then we allow wildcards… Argh. I decided to solve this particular problem like this: if the address is a valid IPv4 address and there is only a single dot afterwards, that dot is “swallowed” as part of the regular IPv4 normalization process that curl always does for IPv4 addresses when parsing URLs. This way, a numerical IPv4 address with a trailing dot will never be passed on to curl internals anymore. And the meaning of the trailing dot for this use case is clear: it is a mistake so we get rid of it. (This also seems to be what browsers do.) Shipping in curl 8.21.0. This choice has already been reported problematic by at least one user who expected a transfer for a URL like this to return error… I suppose this means that the jury is still out on what the best approach for this trailing dot is. What could be more fun than trailing dots if not two trailing dots! Two trailing dots is not possible to use as a hostname when resolving hostnames using DNS. It is an illegal name and causes an error. But as curl provides other ways to populate the DNS cache with a provided name, and you can provide names in etc you can make curl work with URLs where the hostname has two trailing dots. Or rather, you could up until recently until I made sure it is properly banned always because of the trouble they cause internally. A double-dot is correctly treated as a host with a trailing dot, but it turns out that in for example the HSTS logic that became problematic as removing the trailing dot for some functions would still have a trailing dot there when there were two of them to begin with… and it would get confused and act up. No more double trailing dots. One is annoying enough. Shipping in curl 8.21.0. HTTP cookies are basically name/value pairs set by the server and held by the client to get sent back to the server again in later communications. The server can specify for which domain a cookie should apply to, so that it can be used across multiple domains. (Yes, it is a little crazy,) To prevent the server from being able to set the cookie on a too wide domain cookie clients check if the specified domain is Public Suffic Domain (PSL) or not. A server is not allowed to set cookies for PSL domains, as that allows it to create “super cookies” that work across domains in ways that are not allowed. Cookies attempted to get set for such a name should be rejected. In libcurl we check domains against the PSL using the libpsl library . Turns out this too could be tricked by trailing dots. If you communicate with the URL “example.co.uk.” (with a trailing dot) and it sets a cookie for for “co.uk.” (with a trailing dot), the internal check would ask libpsl about the PSL status and… it did not work with trailing dots. The exact same process without trailing dots correctly says it is a PSL and the cookie is refused. But with the trailing dots present it was fooled and curl would allow the cookie to get stored and later sent back to such a host… This particular issue ended up considered a vulnerability known as CVE-2026-8924 . Fix shipped in curl 8.21.0. Yes, you can of course quite correctly argue that none of these things are actually new or sudden changes. Trailing dots are there, they have always been there and people will continue to use them in the future. I’m not blaming anyone else. I’m just expressing my frustration. Trailing dots are the worst.

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daniel.haxx.se Yesterday

a CVE dispute

A few years years ago the curl project signed up and became a CNA . This means that we are masters of and can allocate our own CVE identifiers. For any security problems within our territory, it is we who decides if the issue should get a CVE or not. No more bogus CVEs . During these years we have published fifty-seven separate security vulnerabilities with their associated CVE identifiers. Getting a CVE for an issue is easy and really quickly done when you are a CNA. No hassle, no friction and as we are a small and lean security team it just works as smoothly as you could ask. Just an API call and we have new number. Being a CNA is low maintenance, as there really is nothing extra we need to do. We already had an established and proven process for receiving, managing and assessing vulnerability reports before we became a CNA since we are a responsible and well-run Open Source project. Becoming a CNA just made the process easier as we now don’t need to involve any outsider at all. For every report we work hard to first assess and decide if the issue is actually a vulnerability or a security problem at all. If we deem that there is a security problem in there, we then grade it into LOW, MEDIUM, HIGH or CRITICAL. Since we don’t know how users use curl or libcurl we cannot take that into account but rather observe and set a severity of the problem from a pure curl point of view. It’s a rough indication how we see the problem but of course every user that actually are affected by the problem might rate it differently. For a rare few issues we can imagine that there could be a minuscule risk but because of the set of extreme requirements and convoluted steps to get there, we deem the risk so small that in practice no user is likely to ever reach it. Internally we tend to call that an issue with a severity level lower than LOW. Issues we believe we serve humanity better by not issuing a CVE for. To avoid the security dance when it seems unnecessary. libcurl is installed in somewhere around thirty billion instances on the globe. If we imagine that at least a sizeable portion of those installs are managed by people who want to make sure they use a secure version, it means that every CVE we publish trigger activities in many security teams all over the world, leading to a significant number of patches and subsequent software updates. Every CVE thus has this huge cost tied to it. A cost that does not land on us and we don’t really see or feel it, but a cost on the ecosystem I believe we should not ignore. We should act responsibly. Never ignore real problems of course, but also to make sure we don’t ring the alarm for theoretical problems that will not trigger any vulnerability. Our first ever CVE dispute since we became a CNA reached us on February 10th, 2026 for a report submitted to us two months earlier. The reporter thinks we should have assigned their reported problem a CVE but we think not. Now they want to force the issue to get a CVE anyway, by escalating the situation to MITRE. Yes, it makes you wonder why it is that important to have this as a CVE, but I will avoid speculations for now. I replied to MITRE explaining that we considered and debated the issue and we remain happy with our previous decision. I linked them the original report and discussion to show them. The issue is quite technical (of course) but is based on a bug in curl’s function that checks if the used hostname matches a wildcard provided in a certificate. First: the user must use a hostname in a URL with a leading dot, like This name is not possible to use with DNS (it is an illegal name there), but you can provide an IP address for it in your file or similar, but still this condition is already making this issue really niche. Why would a user ever do this? Well, there could be a redirect to such a host name from a malicious server if the application allows redirects but getting the address for the host is still a challenge and mostly requires a local attacker present add that. Then: if curl can find an address for the illegal DNS hostname, the site curl connects to, also needs to have a wildcard certificate for the name where the tail of the wildcard needs to match the name in the URL. If curl was built to use an OpenSSL flavor or Schannel for TLS (remember that curl supports many different TLS backends), it then calls the function to check if the wildcard covers the used hostname. This function had a bug . The above mention combination then erroneously would return TRUE. A match. When in reality it is not a match according to the spec. We fixed this problem on December 8, 2025 , and we added unit tests for exactly this scenario to make sure that the problem doesn’t come back. For all security issues at several below HIGH, we fix them asap so that was just our normal procedure. We then continued to discuss if this was worthy of a CVE or not. It should be extremely rare that anyone uses a dot prefixed name, unless you are in an internal and controlled environment where you use something else than DNS for resolving. It is not possible to trick an application to use a dot prefixed arbitrary name as it will fail to resolve. The explicitly set, weirdly dot prefixed name, then needs to connect to a host that has a wildcard set for that same name and an attacker manage to run this impostor host and can now serve the application malicious data because curl did not properly reject the connection because of the wildcard mismatch. A series of highly unlikely conditions that all need to be fulfilled for this to become a vulnerability. A lower than LOW situation. Too unlikely; no CVE. On May 28, we were again contacted by MITRE in the same case, asking again for our rationale for not giving this issue a CVE. We responded with virtually the same wording as before and linking again to the same original Hackerone issue and discussion thread. It’s all public information really. On June 15, we were again contacted by MITRE asking for the reasoning behind our decision to not give a CVE for this issue. We replied with similar wording again. Linking to the same issue, again. This seems like a great system. On June 24 we finally got the verdict. It is not considered a security vulnerability.

Security Open Source

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daniel.haxx.se 2 days ago

curl 8.21.0

the 275th release 6 changes 56 days (total: 10,817) 276 bugfixes (total: 14,187) 531 commits (total: 39,077) 0 new public libcurl function (total: 100) 0 new curl_easy_setopt() option (total: 308) 1 new curl command line option (total: 274) 102 contributors, 69 new (total: 3,731) 45 authors, 26 new (total: 1,489) 18 security fixes (total: 206) As mentioned before , the security report volume has been intense lately. We publish eighteen new curl vulnerabilities this time. A new project record for a single release and for the total number of vulnerabilities published within the same calendar year. As always, we have document each vulnerability in detail and I encourage you to read up on the details. The huge focus on vulnerability reports during this release cycle made us merge fewer new features than we wanted, but here are the ones we still managed to get to: We again manage to land more than 250 separate bugfixes, and they are all detailed in the changelog . Planned upcoming removals include: If you are concerned about any of these, speak up on the curl-library list ASAP. Unless we messed up this one and need to do a patch release, the pending next release is scheduled to happen on September 2. This release cycle is extended by two weeks due to the summer of bliss . CVE-2026-8925 : SASL double-free CVE-2026-8927 : env-set cross-proxy Digest auth state leak CVE-2026-9079 : stale proxy password leak CVE-2026-11856 : cross-origin Digest auth state leak CVE-2026-8286 : wrong STARTTLS connection reuse CVE-2026-8458 : wrong reuse for different services CVE-2026-8924 : trailing dot domain super cookie CVE-2026-8926 : password leak with netrc and user in URL CVE-2026-8932 : incomplete mTLS config matching in conn reuse CVE-2026-9080 : UAF after pause in socket callback CVE-2026-9545 : exposing HTTP/3 early data CVE-2026-9546 : sending old referer CVE-2026-9547 : SSH improper host validation CVE-2026-10536 : HTTP/2 stream-dependency tree UAF CVE-2026-11352 : QUIC zero-length UDP datagrams busy-loop CVE-2026-11564 : Native CA trust persist CVE-2026-11586 : WS Auto-PONG memory exhaustion CVE-2026-12064 : proto-default skips SSH verification curl: named globs curl: named globs in output file name for uploads HTTP/3 proxy CONNECT and MASQUE CONNECT-UDP support removed HTTP/2 stream dependency tracking removed support for CURLAUTH_DIGEST_IE added support for SHA256 host public keys with libssh local crypto implementations TLS-SRP support

Programming

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daniel.haxx.se 5 days ago

QUERY with curl

RFC 10008 is brand new a specification detailing the new HTTP method called QUERY: This specification defines the QUERY method for HTTP. A QUERY requests that the request target process the enclosed content in a safe and idempotent manner and then respond with the result of that processing. This is similar to POST requests but can be automatically repeated or restarted without concern for partial state changes For all practical purposes you can think of QUERY as a way to send a GET with a body. It looks exactly like POST, but done with another verb. Contrary to POST, QUERY requests are idempotent – they can be retried or repeated when needed, for instance after a connection failure. You can use curl to do HTTP requests with QUERY just fine. curl offers the option (also known as -X in the short form) that you can use like this: There is one little caveat to remember with this curl option that changes the method. When also asking curl to follow any possible redirects, it is important that you use a new enough curl version because you want the option. Not the old one. Why? Because the old option changes the HTTP method on all subsequent requests independently of what the server responds, which in many cases is not what you want. The newer option instead acts according to what the HTTP response code suggests in should do. Stick to the same method again, or maybe switch to GET in the following request. Why or when would you use this? First of course you only want to use this if the server supports it, but the spec offers some reasons why this might be a good choice: avoid or circumvent URL size limits. Somewhere around 8000 bytes they start to no longer work reliably because servers and intermediaries set limits. expressing certain kinds of data in the URL is inefficient because encoding overhead URLs are more likely to be logged than request content

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daniel.haxx.se 1 weeks ago

curl summer of bliss

The curl project will not accept or otherwise handle any vulnerability reports during the month of July 2026 . We call it the curl summer of bliss . curl’s submission form on Hackerone will be paused starting July 1, 2026. Summer of bliss starts: July 1, 2026 . 00:00 CEST Submissions resume: August 3 2026 . 09:00 CEST The security email address will also be a dead end, as we will not process or otherwise care about security or vulnerability reports sent to us that way either. Whatever issue you find that you feel a need to report to the curl project during this month has to wait. curl’s Hackerone form opens for submissions again on Monday August 3. We do not accept vulnerability reports over email in general, and this fact remains during and after our vacation. The curl maintainers will use this time of less pressure to take in some extra air and to enjoy the summer. Maybe stroll outside a bit more. Breath. Some of us may spend some of this time to see other places. We may get some extra time to spend on fixing bugs or working on new code. Fun stuff! As a direct side-effect of this summer of bliss, to allow us some more time to handle the issues that might have piled up for us in early August, we also push the release date of 8.22.0 two weeks into the future. Now scheduled to happen on September 2, 2026. As previously mentioned, we have been under a huge pressure for the last four months or so. Now we need some rest. We do not expect this deluge to be over. curl’s issue and pull-request trackers on GitHub remain open and active like normal. If you and your Open Source projects also want to participate in the summer of bliss 2026: just do it and let us know! I would of course encourage you to do so. To take care of yourself as a top priority. Probably not. But we will. Then we get to read about it in August. Or you get a support contract and we get to read about it earlier. Everyone with a paid support contracts will of course still get full and appropriate service even during this period. Daniel, in a relaxed state. Credits The ice cream image was made by fotografierende from Pixabay On hacker news .

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daniel.haxx.se 2 weeks ago

A human in control

There seems to be a fair amount of people in either extremes in the current AI landscape. At one side we see the “vibe coders” who use agents and allow them to merge code without any person even looking at the source, while on the other side of the field there are people who are against everything and anything even remotely associated with AI. My personal stance is somewhere in between, as I suppose shouldn’t be too surprising to readers of this blog. The core team behind curl, and that is more people than just me, consists of individuals to whom code quality and source code excellence is important. We do software development because it is a craft we love and we are proud of what we have accomplished this far. We do not hand over our responsibilities to any machines. We stand for every bit of code we merge – as humans. Blindly accepting code written by AI means that you merge a certain amount of errors, but this is certainly true for human written code as well, so this is not in itself special. Some data suggests that AI generated code might even contain more mistakes than the human versions. We invented test cases and code review a long time ago as a means to help us combat and reduce mistakes to get merged. The particular way code was written does not take away the benefits from code review and getting additional checks and eyes on pending changes. A good code review helps spotting mistakes, omissions or slip-ups. It also helps reinforce the architecture and established design choices. This is true however the code was created. This far, code reviews done by automatic AI bots and the likes have not yet managed to replace the humans. They are simply not good enough. Human reviews are much better. They catch other things and they help make sure proposed changes stay on track. Not to mention how I want to know how curl works, even if I don’t keep 100% intimate knowledge of every single angle and corner, I know most of it. I think it helps me make better decisions, debug better, help users better and keep the architecture sound. Getting the initial code written is not the big deal. For curl, maintaining and polishing the landed code through decades is the real task. Everything we merge in curl is determined fine and fitting by humans. In all living software projects we get bugs reported and we fix them. We do new releases and continue to iterate. We have done this since software was invented and we still do, as humans are quite fallible and easily make mistakes. We try to reduce the error density and frequency by adding tests and by adding more human eyes on the code before we green-light it. It helps, but is not perfect. To help us do better code we invent, introduce and enforce a wide variety of different tools. With tools that look at code and identify problems in the early stages, they help avoid landing bad code in the first place. They make us do better code. They reduce the bug frequency. Some of the best tools for detecting coding mistakes today use AI. These tools might work on existing source code in a git repository or they might look at proposed changes in pull-requests. Above I mentioned that human code reviews are better; but the opposite is also true. In a somewhat complicated change request, it is now common that after the humans can’t spot any more problems, the AI PR review bots can still find an issue or two to remark on. Sure, sometimes they are wrong and then the comment is easily dismissed, but more often than not the findings they point out are actually something worth addressing before merge. curl is developed and driven by humans, assisted by tools. Open Source is about sharing code and is a development model where we do things in the open. The communication part of this model is key. Share your ideas, your visions, your problems or maybe just your ideas for what to do this afternoon. Express what you want or what the problem is, and the team can respond and we can work together on fixing and improving whatever needs to be done. Effective communication, a condition for good Open Source, implies human-to-human interaction. Inserting a large AI generated tone-deaf large wall-of-text into such a flow can still work, but only in the same way humans can learn to work with difficult individuals as well. It is not ideal and it is not a smooth way of working. It introduces sand in the machine. Don’t do that. It is rude. Effective Open Source work means we communicate as humans, even if parts of the work and the code is made with the help of AI. Humans and machines excel at different things. We can complement each other in software development. Everyone is free to act to their own will, but in the curl project we don’t hand over responsibility to machines. We stand for our product. We make it as good as we possibly can; using all the tools that are available to us. I claim that in order to do this, humans need to remain in control.

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daniel.haxx.se 4 weeks ago

curl up 2026 summary

Getting curl developers and related enthusiasts into a single room to hang out in the real world for a whole weekend once a year is awesome. We find inspiration, we share experiences, we learn from each other and we dream and plan of future endeavors and things to work on. Seeing faces, hearing voices and watching body language help us communicate better virtually and on video calls during the rest of the year. We have gathered curl people like this annually since 2017, even if some years during Covid were “different”. To me, this is one of the best events of the year. I get to hang out and talk curl with good friends a whole weekend! The 2026 edition was held in Prague in late May and kept the general style of past events. About 25 people got into the room. We had five curl maintainers present and quite a lot of local curious minds. The curl up format is easy, casual and friendly. We do topical presentations, followed up with Q&A and discussions around the topics brought up – of course usually with reflections about curl’s role, both past and future. We live-stream and record the presentations to allow our friends who could not attend to keep up both in real-time but also after the fact. Unfortunately the tech is not always on our side so the quality sometimes is a little lacking. This year I brought an HDMI-splitter and an HDMI-to-USB device to allow us to get better recordings, but they were not working as smoothly as intended so we had to use inferior backup solutions for most of the meetup. This presentation above was the “keynote”, the introduction talk to the event. We then also recorded another nine session that are all available in the curl up 2026 playlist on YouTube. To give you all a little glimpse of what curl up is about, here’s a gallery showing some of the speakers and some scenery. Daniel Stenberg Alexandr Nedvedicky Daniel Stenberg Jim Fuller Jim Fuller Carlos Henrique Lima Melara Jim Klimov Moritz Buhl Stanislav Fort Daniel Stenberg Igor Chubin Igor Chubin Daniel Stenberg Daniel Stenberg and Frank Gevaerts All photos taken by and donated to us by an anonymous curl fan present in the room.

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daniel.haxx.se 1 months ago

The pressure

I’m doing Open Source primarily because I love it. The social aspects, the for-the-good angle and for the challenge of engineering this to work for everyone. I also do it because it is my full-time job and getting food on the table and provide for my family is not unimportant. It may come as a shock, but I am not in this game for the money or the extravagant life style. I have been working full-time on curl since 2019. For me, this typically means doing 50 hour work weeks, as I spend all days on it and then I top them off with a few more hours every late night – all days of the week, I spend all this time on curl because it is a work of love and it is both my job and my spare time hobby and no one counts my hours anyway. (And no, I do not recommend anyone else to do the same. I’m not suggesting this for others.) I consider my primary work-related mission in life to be to make curl the best transfer library and tool possible and make it qualify as a top project in Open Source, quality, performance and not the least, security. I believe we generally meet these lofty goals. I founded the curl project, I am still a lead developer in the project almost thirty years later. While I always clearly state that curl is not a one-man shop and that curl would absolutely not be what it is without my awesome curl team mates, a large part of the world still thinks of curl as my project and sometimes more or less equals curl with my person. I cannot help to take curl issues personally. When someone critiques curl, it is by extension a complaint on decisions and choices I stand by and behind – and many cases I made the calls. curl is personal to me. curl has formed my life forever. I have two kids. They were both born many years after I started working on curl and they are both adults and independent individuals now. I love them dearly. Life passes by but curl remains. We’ve had slow times and busy times. The decades pass. Later this year the curl project celebrates thirty years. We typically repeat that the number of curl installations in the world is perhaps thirty billion. Over the last years I have done numerous blog posts on the state of security reports submitted to curl. They have gradually switched over from complaints on stupid LLMs , to stupid AI slop reports , closing the bug bounty over to the current high quality chaos which for us started maybe at some point in March 2026. We have seen many spectacular security failures through the years, in Internet products, in software infrastructure and in Open Source. Every time we read about those events, we get reminded about how curl is everywhere and how we really really really do not want anything such to happen to us or our users. And we take another lap around the project, tighten every bolt a little more, add a few more checks, tests and guidelines to ideally make the curl ship ever so slightly less likely to ever leak or sink. Recently, after I pointed out that Mythos only found a single low severity problem in curl in its first scan, countless people have repeated the claim that curl is one of the most scrutinized, most reviewed, most fuzzed and most verified source codes you can imagine. Perhaps that’s true, but I just want to mention this: that’s not by mistake. That’s not an accident or a happy circumstance. That’s the result of relentless work and attention to details through decades. Software engineering done right . Iterative improvements over time that simply never ends is an effective method. This does not however mean that we don’t have bugs or that we don’t have security problems left, because we do. We have hundreds of thousands of lines of source code that is doing highly parallel networking for many protocols on all imaginable operating systems and CPU architectures – in C. So we fix the problems, patch them up and ship new releases. Over and over. Thirty billion installations world-wide means that everyone reading this blog post has curl installed multiple times in stuff they own. In phones, tablets, cars, TVs, printers, game consoles, kitchen equipment and more. Not to mention all the online digital services we use and those devices communicate with. I cannot stress the importance of curl security and I would guess that most of you agree with me. I am jealous of those projects that shipped a horrible bug at some point in the past that made the world burn for a while. They got attention and some of them then got funding and financial muscles to get them staff and hire multiple full time engineers. I sometimes think we would be better off if we also had one of those. A thirty years old project could make you think you’ve seen most things already, but we have not been in this situation before. The rate of incoming security reports is 4-5 times higher than it was in 2024 and double the speed of 2025 – meaning that on average we now get more than one report per day . The quality is way higher than ever before. The reports are typically very detailed and long. In order to manage this incoming flood of submissions, we need to make sure to handle them as soon as possible as we know there are more coming. If we don’t take care of them roughly at the same speed they arrive, the backlog just grows and having that list of potential security problems in a list that you don’t have control over takes a mental toll. I spend almost all my days right now working through the list of reported security issues that we have on Hackerone. Verify the claim, assess the importance, write a patch, figure out when the bug was introduced, understand the vulnerability, write a detailed advisory explaining the problem to the world and communicate all this with the security researcher and the rest of the curl security team. For the first time in my life, my wife voiced concerns about my work hours and my imbalanced work/life situation. I work more than I’ve done before, but the flood keeps coming. People in my surrounding, I guess reading between the lines, have asked me how I and we cope with this deluge and want to make sure we don’t burn in the process. I am concerned for my team mates. I might soon have to reduce my work hours to allow myself more breathing time. This is a never-before seen or experienced pressure on the curl project and its security team members. An avalanche of high priority work that trumps all other things in the project that is primarily mental because we certainly could ignore them all if we wanted, but we feel a responsibility, we have a conscience and we are proud about our work. We feel obliged to fix security problems in the software we have helped shipped to every device on the globe. This is personal to us. With about half the release cycle left until the pending release ships, we already have twelve confirmed vulnerabilities meaning twelve pending CVE announcements. That’s a new project record and it also means we will reach thirty published CVEs in 2026 even before half the calendar year has passed. The projected total amount of curl CVEs published through the whole year is therefore at least double this number! What help would we like? Short term it is a little late. We already have work up to our ears. I wish more companies that use and depend upon curl or libcurl in commercial software and services would chime in their part to fund us. We could then pay more developers to distribute the work load across. That would be great. Feel free to contact me to discuss how you can contribute to this. Get your employer to pay for a support contract! Fortunately we have customers who already do this, so some of us can work on curl full time. I am a pragmatic (and a bit of a cynic) and I have danced this dance for a long time already. I have no illusions that anything significant is going to change in this area even if we are in an unparalleled situation and in a tighter spot than ever before. I totally expect us to ride out this storm by ourselves. Like we are used to. We will survive. We will endure. It might just be a bit of a shaky period in the project and in the world at large as we try to maneuver our way through this. There’s a tsunami coming over us and all we can do is swim, there are no life boats for us. The curl project is not owned by a company. We are not part of any umbrella organization. This makes us a little under-powered at times, but it also gives us maximum freedom and flexibility. We act solely in the interest of making curl as good as possible for the world and curl users. Fixing bugs and problems is good. Every reported problem implies a fixed issue. curl becomes a better product. What is also a good trend: almost no one finds terrible vulnerabilities. All vulnerabilities found the last few years in curl have all been deemed severity LOW or MEDIUM. I’m not saying there won’t be any more HIGH ever, but at least they are rare. The most recent severity high curl CVE was published in October 2023. Right now we are under a little pressure. Forgive us if we are a little slow to respond sometimes. Image by Brian Merrill from Pixabay

Career Open Source Security

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daniel.haxx.se 1 months ago

named globs with curl

One of the established power features of the curl command line tool is its support for “globbing”. It is a built-in way to specify ranges and sets in different ways and have curl iterate over them to simplify repeated transfers. For example, you can easily download three images from the same host without having to repeat the almost same URL three times: Or if you have them in a numbered range, you can get a thousand images in a single tiny command line: And they can be combined in crazy ways: curl allows globs used in a single URL to create up to 2 63 permutations – which, if you can do one million transfers per second, would take 292 thousand years to complete. (As an added bonus you can of course also add to the command line to make curl transfer all those images in parallel rather than serially.) To help users save files when using globbing, curl provides a way to reference the globbed components using when setting the target filename. The number then references the specific glob, where the first is 1, the second 2 etc. Saving the one thousand images using different filenames locally than they use remotely: This allows a compact command line to also offer flexibility. All functionality mentioned above has existed in curl for years; decades even. It just so happened that one day when working with curl I fell over a use case that I could not solve with the existing command line functionality. I wanted to do a globbed upload to a HTTP server and then save all the separate responses into their own dedicated files, preferably with names based on the glob. I will admit that I at first had a hard time to accept the fact that we actually could not do this already, but that was then rather quickly instead turned into: how should I add support for this in the smoothest and most convenient way? Using what syntax? The road to fixing it for uploads took a little detour. Starting in 8.21.0, curl can assign a name to each glob and then reference that glob by name instead of using just a glob index number. This allows command lines to get ever so slightly more readable I think. The image range example from above, but instead using named globs: Or a version with three separate globs where they all are used in the output file name: Slick, right? Back to the globbed upload challenge: … but with the responses saved in separate files instead of sent to stdout. Use named globs: The only way to refer to an upload glob is to set a name and refer to that name. There are no indexed references for uploads, only for URL globs. It is in fact possible to also use a mix of upload globs and URL globs in the same command line if you want to upload multiple files to multiple destinations. They set the names in the same namespace and you refer to the names the same way, independently of source. This feels more like a thing to show off in a blog post like this rather than something people will actually find good use for: Upload three files to three sites, save all nine response in separate files:

Programming

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daniel.haxx.se 1 months ago

Mythos finds a curl vulnerability

yes, as in singular one . Back in April 2026 Anthropic caused a lot of media noise when they concluded that their new AI model Mythos is dangerously good at finding security flaws in source code. Apparently Mythos was so good at this that Anthropic would not release this model to the public yet but instead trickle it out to a selected few companies for a while to allow a few good ones(?) to get a head start and fix the most pressing problems first, before the general populace would get their hands on it. The whole world seemed to lose its marbles. Is this the end of the world as we know it? An amazingly successful marketing stunt for sure. Part of the deal with project Glasswing was that Anthropic also offered access to their latest AI model to “Open Source projects” via Linux Foundation . Linux Foundation let their project Alpha Omega handle this part, and I was contacted by their representatives. As lead developer of curl I was offered access to the magic model and I graciously accepted the offer. Sure, I’d like to see what it can find in curl. I signed the contract for getting access, but then nothing happened. Weeks went past and I was told there was a hiccup somewhere and access was delayed. Eventually, I was instead offered that someone else, who has access to the model, could run a scan and analysis on curl for me using Mythos and send me a report. To me, the distinction isn’t that important. It’s not that I would have a lot of time to explore lots of different prompts and doing deep dive adventures anyway. Getting the tool to generate a first proper scan and analysis would be great, whoever did it. I happily accepted this offer. (I am purposely leaving out the identity of the individual(s) involved in getting the curl analysis done as it is not the point of this blog post.) Before this first Mythos report, we had already scanned curl with several different very capable AI powered tools (I mean in addition to running a number of “normal” static code analyzers all the time, using the pickiest compiler options and doing fuzzing on it for years etc). Primarily AISLE , Zeropath and OpenAI’s Codex Security have been used to scrutinize the code with AI. These tools and the analyses they have done have triggered somewhere between two and three hundred bugfixes merged in curl through-out the recent 8-10 months or so. A bunch of the findings these AI tools reported were confirmed vulnerabilities and have been published as CVEs. Probably a dozen or more. Nowadays we also use tools like GitHub’s Copilot and Augment code to review pull requests, and their remarks and complaints help us to land better code and avoid merging new bugs. I mean, we still merge bugs of course but the PR review bots regularly highlight issues that we fix: our merges would be worse without them. The AI reviews are used in addition to the human reviews. They help us, they don’t replace us. We also see a high volume of high quality security reports flooding in : security researchers now use AI extensively and effectively. Security is a top priority for us in the curl project. We follow every guideline and we do software engineering properly, to reduce the number of flaws in code. Scanning for flaws is just one of many steps to keep this ship safe. You need to search long and hard to find another software project that makes as much or goes further than curl, for software security. Steps involved in keeping curl secure May 6, 2026 It was with great anticipation we received the first source code analysis report generated with Mythos. Another chance for us to find areas to improve and bugs to fix. To make an even better curl. This initial scan was made on curl’s git repository and its master branch of a certain recent commit . It counted 178K lines of code analyzed in the src/ and lib/ subdirectories. The analysis details several different approaches and methods it has performed the search, and how it has focused on trying to find which flaws. A fun note in the top of the report says: curl is one of the most fuzzed and audited C codebases in existence (OSS-Fuzz, Coverity, CodeQL, multiple paid audits). Finding anything in the hot paths (HTTP/1, TLS, URL parsing core) is unlikely. … and it correctly found no problems in those areas. Completely unscientific poll on Mastodon about people’s expectations for Mythos scanning curl The size of curl curl is currently 176,000 lines of C code when we exclude blank lines. The source code consists of 660,000 words, which is 12% more words than the entire English edition of the novel War and Peace. On average, every single production source code line of curl has been written (and then rewritten) 4.14 times. We have polished on this. Right now, the existing production code in git master that still remains, has been authored by 573 separate individuals. Over time, a total of 1,465 individuals have so far had their proposed changes merged into curl’s git repository. We have published 188 CVEs for curl up until now. curl is installed in over twenty billion instances . It runs on over 110 operating systems and 28 CPU architectures . It runs in every smart phone, tablet, car, TV, game console and server on earth. The report concluded it found five “Confirmed security vulnerabilities”. I think using the term confirmed is a little amusing when the AI says it confidently by itself. Yes, the AI thinks they are confirmed, but the curl security team has a slightly different take. Five issues felt like nothing as we had expected an extensive list. Once my curl security team fellows and I had poked on the this short list for a number of hours and dug into the details, we had trimmed the list down and were left with one confirmed vulnerability. The other four were three false positives (they highlighted shortcomings that are documented in API documentation) and the fourth we deemed “just a bug”. The single confirmed vulnerability is going to end up a severity low CVE planned to get published in sync with our pending next curl release 8.21.0 in late June. The flaw is not going to make anyone grasp for breath. All details of that vulnerability will of course not get public before then, so you need to hold out for details on that. The Mythos report on curl also contained a number of spotted bugs that it concluded were not vulnerabilities, much like any new code analyzer does when you run it on hundreds of thousands of lines of code. All the bugs in the report are being investigated and one by one we are fixing those that we agree with. All in all about twenty bugs that are described and explained very nicely. Barely any false positives, so I presume they have had a rather high threshold for certainty. curl is certainly getting better thanks to this report, but counted by the volume of issues found, all the previous AI tools we have used have resulted in larger bugfix amounts. This is only natural of course since the first tools we ran had many more and easier bugs to find. As we have fixed issues along the way, finding new ones are slowly becoming harder. Additionally, a bug can be small or big so it’s not always fair to just compare numbers My personal conclusion can however not end up with anything else than that the big hype around this model so far was primarily marketing. I see no evidence that this setup finds issues to any particular higher or more advanced degree than the other tools have done before Mythos. Maybe this model is a little bit better, but even if it is, it is not better to a degree that seems to make a significant dent in code analyzing. This is just one source code repository and maybe it is much better on other things. I can only tell and comment on what it found here. But allow me to highlight and reiterate what I have said before: AI powered code analyzers are significantly better at finding security flaws and mistakes in source code than any traditional code analyzers did in the past. All modern AI models are good at this now. Anyone with time and some experimental spirits can find security problems now. The high quality chaos is real. Any project that has not scanned their source code with AI powered tooling will likely find huge number of flaws, bugs and possible vulnerabilities with this new generation of tools. Mythos will, and so will many of the others. Not using AI code analyzers in your project means that you leave adversaries and attackers time and opportunity to find and exploit the flaws you don’t find. Zero memory-safety vulnerabilities found. Methodology note: this review is hand-driven analysis using LLM subagents for parallel file reads, with every candidate finding re-verified by direct source inspection in the main session before being recorded. The CVE to variant-hunt mapping was built from curl’s own vuln.json. No automated SAST tooling was used. This outcome is consistent with curl’s status as one of the most heavily fuzzed and audited C codebases. The defensive infrastructure (capped dynbufs everywhere, with explicit max on every numeric parse, overflow guard, CURL_PRINTF format-string enforcement, per-protocol response-size caps, pingpong 64KB line cap) systematically closes the bug classes that would normally be productive in a codebase this size. Coverage now includes: all minor protocols, all file parsers, all TLS backends’ verify paths, http/1/2/3, ftp full depth, mprintf, x509asn1, doh, all auth mechanisms, content encoding, connection reuse, session cache, CLI tool, platform-specific code, and CI/build supply chain. It should be noted that the AI tools find the usual and established kind of errors we already know about. It just finds new instances of them. We have not seen any AI so far report a vulnerability that would somehow be of a novel kind or something totally new. They do not reinvent the field in that way, but they do dig up more issues than any other tools did before. These were absolutely not the last bugs to find or report. Just while I was writing the drafts for this blog post we have received more reports from security researchers about suspected problems. The AI tools will improve further and the researchers can find new and different ways to prompt the existing AIs to make them find more. We have not reached the end of this yet. I hope we can keep getting more curl scans done with Mythos and other AIs, over and over until they truly stop finding new problems. Thanks to Anthropic and Alpha Omega for providing the model, the tools and doing the scan for us. Thanks also to the individual who did the scan for us. Much appreciated! Top image by Jin Kim from Pixabay Thanks for flying curl. It’s never dull. They can spot when the comment says something about the code and then conclude that the code does not work as the comment says. It can check code for platforms and configurations we otherwise cannot run analyzers for It “knows” details about 3rd party libraries and their APIs so it can detect abuse or bad assumptions. It “knows” details about protocols curl implements and can question details in the code that seem to violate or contradict protocol specifications They are typically good at summarizing and explaining the flaw, something which can be rather tedious and difficult with old style analyzers. They can often generate and offer a patch for its found issue (even if the patch usually is not a 100% fix).

Open Source C Security JSON

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daniel.haxx.se 1 months ago

Approaching zero bugs?

In this era of powerful tools to find software bugs , we now see tools find a lot of problems at a high speed. This causes problems for developers, as dealing with the growing list of issues is hard. It may take a longer time to address the problems than to find them – not to mention to put them into releases and then it takes yet another extended time until users out in the wild actually get that updated version into their hands. In order to find many bugs fast, they have to already exist in source code. These new tools don’t add or create the problems. They just find them, filter them out and bring them to the surface for exposure. A better filter in the pool filters out more rubbish. The more bugs we fix, the fewer bugs remain in the code. Assuming the developers manage to fix problems at a decent enough pace. For every bugfix we merge, there is a risk that the change itself introduces one more more new separate problems. We also tend to keep adding features and changing behavior as we want to improve our products, and when doing so we occasionally slip up and introduce new problems as well. Source code analyzing tools is a concept as old as source code itself. There has always existed tools that have tried to identify coding mistakes. Now they just recently got better so they can find more mistakes. These new tools, similar to the old ones, don’t find all the problems. Even these new modern tools sometimes suggest fixes to the problems they find that are incomplete and in fact sometimes downright buggy. Undoubtedly code analyzer tooling will improve further. The tools of tomorrow will find even more bugs, some of them were not found when the current generation of tools scanned the code yesterday. Of course, we now also introduce these tools in CI and general development pipelines, which should make us land better code with fewer mistakes going forward. Ideally. If we assume that we fix bugs faster than we introduce new ones and we assume that the AI tools can improve further, the question is then more how much more they can improve and for how long that improvement can go on. Will the tools find 10% more bugs? 100%? 1000%? Is the tool improving going to gradually continue for the next two, ten or fifty years? Can they actually find all bugs? Can we reach the utopia where we have no bugs left in a given software project and when we do merge a new one, it gets detected and fixed almost instantly? If we assume that there is at least a theoretical chance to reach that point, how would we know when we reach it? Or even just if we are getting closer? I propose that one way to measure if we are getting closer to zero bugs is to check the age of reported and fixed bugs. If the tools are this good, we should soon only be fixing bugs we introduced very recently. In the curl project we don’t keep track of the age of regular bugs, but we do for vulnerabilities. The worst kind of bugs. If the tools can find almost all problems, they should soon only be finding very recently added vulnerabilities too. The age of new finds should plummet and go towards zero. If the age of newly reported vulnerabilities are getting younger, it should make the average and median age of the total collection go down over time. The average and median time vulnerabilities had existed in the curl source code by the time they were found and reported to the project. Accumulated vulnerability age when reported Bugfixes When the tools have found most problems there should be less bugs left to fix. The bugfix rate should go down rapidly – independently of how you count them or how liberal we are in counting exactly what is a bugfix. Bugfixes Given the data from the curl project, there does not seem to be fewer bugfixes done – yet. Maybe the bugfix speed goes up before it goes down? Given the look of these graphs I don’t think we are close to zero bugs yet. These two curves do not seem to even start to fall yet. Yes, these graphs are based on data from a single project, which makes it super weak to draw statistical conclusions from, but this is all I have to work with. I think that’s mostly an indication of what you believe the tooling can do and how good they can eventually end up becoming. I don’t know. I will keep fixing bugs.

DevOps Programming Testing

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daniel.haxx.se 1 months ago

Inspired

The picture was taken by mr Nasser and shared on social media In appendix A of the book Root cause: Stories and lessons from two decades of Backend Engineering Bugs , author Hussein Nasser has these wonderful words to say about me: Daniel Stenberg is a Swedish engineer and the creator of curl (cURL), one of the most widely used tools and libraries for fetching content over various protocols. I’ve always admired Daniel’s work, reading his blogs and watching his talks on YouTube. He is one of the engineers who inspired me to start my own YouTube channel and teach backend engineering. It warms my heart to read this. Words like this give me energy and motivation. My work has meaning.

Open Source Backend

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daniel.haxx.se 1 months ago

curl 8.20.0

You always find the new curl releases on the curl site ! the 274th release 8 changes 49 days (total: 10,761) 282 bugfixes (total: 13,922) 521 commits (total: 38,545) 0 new public libcurl function (total: 100) 0 new curl_easy_setopt() option (total: 308) 0 new curl command line option (total: 273) 73 contributors, 45 new (total: 3,664) 28 authors, 12 new (total: 1,463) 8 security fixes (total: 188) As mentioned elsewhere , the security reporting volume has been intense lately. We publish eight new curl vulnerabilities this time. The official count says over 260 bugfixes were merged in this 49 day cycle. See the changelog for all the details. Planned upcoming removals include: If you are concerned about any of these, speak up on the curl-library ASAP. Unless we messed up this one and need to do a patch release, the pending next release is scheduled to happen on June 24. CVE-2026-7168: cross-proxy Digest auth state leak CVE-2026-7009: OCSP stapling bypass with Apple SecTrust CVE-2026-6429: netrc credential leak with reused proxy connection CVE-2026-6276: stale custom cookie host causes cookie leak CVE-2026-6253: proxy credentials leak over redirect-to proxy CVE-2026-5773: wrong reuse of SMB connection CVE-2026-5545: wrong reuse of HTTP Negotiate connection CVE-2026-4873: connection reuse ignores TLS requirement now uses a thread pool and queue for resolving NTLM is disabled by default dropped support for CMake 3.17 and older dropped support for < c-ares 1.16.0 SMB is disabled by default added CURLMNWC_CLEAR_ALL for all network changes dropped RTMP support local crypto implementations TLS-SRP support

Open Source Security

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daniel.haxx.se 2 months ago

High-Quality Chaos

As I have been preparing slides for my coming talk at foss-north on April 28, 2026 I figured I could take the opportunity and share a glimpse of the current reality here on my blog. The high quality chaos era, as I call it. I complained and I complained about the high frequency junk submissions to the curl bug-bounty that grew really intense during 2025 and early 2026. To the degree that we shut it down completely on February 1st this year. At the time we speculated if that would be sufficient or if the flood would go on. Now we know. In March 2026, the curl project went back to Hackerone again once we had figured out that GitHub was not good enough. From that day, the nature of the security report submissions have changed. The slop situation is not a problem anymore. AI slop rate The report frequency is higher than ever. Recently it’s been about double the rate we had through 2025, which already was more than double from previous years. Number of hours between security reports The quality is higher. The rate of confirmed vulnerabilities is back to and even surpassing the 2024 pre-AI level, meaning somewhere in the 15-16% range. Confirmed vulnerability rate In addition to that, the share of reports that identify a bug, meaning that they aren’t vulnerabilities but still some kind of problem, is significantly higher than before. Share of reports that were bugs, not vulnerabilities Everything is AI now Almost every security report now uses AI to various degrees. You can tell by the way they are worded, how the report is phrased and also by the fact that they now easily get very detailed duplicates in ways that can’t be done had they been written by humans. The difference now compared to before however, is that they are mostly very high quality. The reporters rarely mention exactly which AI tool or model they used (and really, we don’t care), but the evidence is strong that they used such help. I did a quick unscientific poll on Mastodon to see if other Open Source projects see the same trends and man, do they! Friends from the following projects confirmed that they too see this trend. Of course the exact numbers and volumes vary, but it shows its not unique to any specific project. Apache httpd, BIND, curl, Django, Elasticsearch Python client, Firefox, git, glibc, GnuTLS, GStreamer, Haproxy, Immich, libssh, libtiff, Linux kernel, OpenLDAP, PowerDNS, python, Prometheus, Ruby, Sequoia PGP, strongSwan, Temporal, Unbound, urllib3, Vikunja, Wireshark, wolfSSL, … I bet this list of projects is just a random selection that just happened to see my question. You will find many more experiencing and confirming this reality view. When we ship curl 8.20.0 in the middle of next week – end of April 2026, we expect to announce at least six new vulnerabilities. Assuming that the trend keeps up for at least the rest of the year, and I think that is a fair assumption, we are looking at an estimated explosion and a record amount of CVEs to be published by the curl project this year. We might publish closer to 50 curl vulnerabilities in 2026. Number of published vulnerabilities Given this universal trend, I cannot see how this pattern can not also be spotted and expected to happen in many other projects as well. The tools are still improving. We keep adding flaws when we do bugfixes and add new features. Someone has suggested it might work as with fuzzing, that we will see a plateau within a few years. I suppose we just have to see how it goes. This avalanche is going to make maintainer overload even worse. Some projects will have a hard time to handle this kind of backlog expansion without any added maintainers to help. It is probably a good time for the bad guys who can easily find this many problems themselves by just using the same tools, before all the projects get time, manpower and energy to fix them. Then everyone needs to update to the newly released fixed versions of all packages, which we know is likely to take an even longer time. We are up for a bumpy ride.

Security AI Open Source Python Ruby

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daniel.haxx.se 3 months ago

Don’t trust, verify

Software and digital security should rely on verification , rather than trust. I want to strongly encourage more users and consumers of software to verify curl. And ideally require that you could do at least this level of verification of other software components in your dependency chains. With every source code commit and every release of software, there are risks. Also entirely independent of those. Some of the things a widely used project can become the victim of, include… In the event any of these would happen, they could of course also happen in combinations and in a rapid sequence. curl, mostly in the shape of libcurl, runs in tens of billions of devices. Clearly one of the most widely used software components in the world. People ask me how I sleep at night given the vast amount of nasty things that could occur virtually at any point. There is only one way to combat this kind of insomnia: do everything possible and do it openly and transparently. Make it a little better this week than it was last week. Do software engineering right. Provide means for everyone to verify what we do and what we ship. Iterate, iterate, iterate. If even just a few users verify that they got a curl release signed by the curl release manager and they verify that the release contents is untainted and only contains bits that originate from the git repository, then we are in a pretty good state. We need enough independent outside users to do this, so that one of them can blow the whistle if anything at any point would look wrong. I can’t tell you who these users are, or in fact if they actually exist, as they are and must be completely independent from me and from the curl project. We do however provide all the means and we make it easy for such users to do this verification . The few outsiders who verify that nothing was tampered with in the releases can only validate that the releases are made from what exists in git. It is our own job to make sure that what exists in git is the real thing . The secure and safe curl. We must do a lot to make sure that whatever we land in git is okay. Here’s a list of activities we do. All this done in the open with full transparency and full accountability. Anyone can follow along and verify that we follow this. Require this for all your dependencies. We plan for the event when someone actually wants and tries to hurt us and our users really bad. Or when that happens by mistake. A successful attack on curl can in theory reach widely . This is not paranoia. This setup allows us to sleep well at night. This is why users still rely on curl after thirty years in the making. I recently added a verify page to the curl website explaining some of what I write about in this post. Jia Tan is a skilled and friendly member of the project team but is deliberately merging malicious content disguised as something else. An established committer might have been breached unknowingly and now their commits or releases contain tainted bits. A rando convinced us to merge what looks like a bugfix but is a small step in a long chain of tiny pieces building up a planted vulnerability or even backdoor Someone blackmails or extorts an existing curl team member into performing changes not otherwise accepted in the project A change by an established and well-meaning project member that adds a feature or fixes a bug mistakenly creates a security vulnerability. The website on which tarballs are normally distributed gets hacked and now evil alternative versions of the latest release are provided, spreading malware. Credentials of a known curl project member is breached and misinformation gets distributed appearing to be from a known and trusted source . Via email, social media or websites. Could even be this blog! Something in this list is backed up by an online deep-fake video where a known project member seemingly repeats something incorrect to aid a malicious actor. A tool used in CI, hosted by a cloud provider, is hacked and runs something malicious While the primary curl git repository has a downtime, someone online (impersonating a curl team member?) offers a temporary “curl mirror” that contains tainted code. we have a consistent code style (invalid style causes errors). This reduces the risk for mistakes and makes it easier to debug existing code. we ban and avoid a number of “sensitive” and “hard-to-use” C functions (use of such functions causes errors) we have a ceiling for complexity in functions to keep them easy to follow, read and understand (failing to do so causes errors) we review all pull requests before merging, both with humans and with bots. We link back commits to their origin pull requests in commit messages. we ban use of “binary blobs” in git to not provide means for malicious actors to bundle encrypted payloads (trying to include a blob causes errors) we actively avoid base64 encoded chunks as they too could function as ways to obfuscate malicious contents we ban most uses of Unicode in code and documentation to avoid easily mixed up characters that look like other characters. (adding Unicode characters causes errors) we document everything to make it clear how things are supposed to work. No surprises. Lots of documentation is tested and verified in addition to spellchecks and consistent wording. we have thousands of tests and we add test cases for (ideally) every functionality. Finding “white spots” and adding coverage is a top priority. curl runs on countless operating systems, CPU architectures and you can build curl in billions of different configuration setups: not every combination is practically possible to test we build curl and run tests in over two hundred CI jobs that are run for every commit and every PR. We do not merge commits that have unexplained test failures. we build curl in CI with the most picky compiler options enabled and we never allow compiler warnings to linger. We always use that converts warnings to errors and fail the builds. we run all tests using valgrind and several combinations of sanitizers to find and reduce the risk for memory problems, undefined behavior and similar we run all tests as “torture tests”, where each test case is rerun to have every invoked fallible function call fail once each, to make sure curl never leaks memory or crashes due to this. we run fuzzing on curl: non-stop as part of Google’s OSS-Fuzz project, but also briefly as part of the CI setup for every commit and PR we make sure that the CI jobs we have for curl never “write back” to curl. They access the source repository read-only and even if they would be breached, they cannot infect or taint source code. we run and other code analyzer tools on the CI job config scripts to reduce the risk of us running or using insecure CI jobs. we are committed to always fix reported vulnerabilities in the following release. Security problems never linger around once they have been reported. we document everything and every detail about all curl vulnerabilities ever reported our commitment to never breaking ABI or API allows all users to easily upgrade to new releases. This enables users to run recent security-fixed versions instead of legacy insecure versions. our code has been audited several times by external security experts, and the few issues that have been detected in those were immediately addressed Two-factor authentication on GitHub is mandatory for all committers

Security Open Source

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daniel.haxx.se 3 months ago

One hundred weirdo emails

I hope I don’t have to spell it out but I will do it anyway: in these cases I don’t know anything about their products and I cannot help them. Quite often I first need to search around only to figure out what the product is or does, that the person asks me about. Over the years I have collected such emails that end up in my inbox. Out of those that I have received, I have cherry-picked my favorites: the best, the weirdest, the most offensive and the most confused ones and I put them up online . A few of then also triggered separate blog posts of their own in the past. They help us remember that the world is complicated and hard to understand . Today, my online collection reached the magical amount: 100 emails. The first one in the stash was received in 2009 and the latest arrived just the other day. I expect I’ll keep adding occasional new ones going forward as well. My email address is spelled out in the curl license The curl license appears in many products Some people have problems with their products and need someone to email A few of these discover my email in their product Occasionally, the person in need of help emails me about their product. I collect some of those and make them public

Open Source

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daniel.haxx.se 3 months ago

NTLM and SMB go opt-in

The NTLM authentication method was always a beast. It is a proprietary protocol designed by Microsoft which was reverse engineered a long time ago. That effort resulted in the online documentation that I based the curl implementation on back in 2003. I then also wrote the NTLM code for wget while at it. NTLM broke with the HTTP paradigm: it is made to authenticate the connection instead of the request , which is what HTTP authentication is supposed to do and what all the other methods do. This might sound like a tiny and insignificant detail, but it has a major impact in all HTTP implementations everywhere. Indirectly it is also the cause for quite a few security related issues in HTTP code, because NTLM needs many special exceptions and extra unique treatments. curl has recorded no less than seven past security vulnerabilities in NTLM related code! While that may not be only NTLM’s fault, it certainly does not help. The connection-based concept also makes the method incompatible with HTTP/2 and HTTP/3. NTLM requires services to stick to HTTP/1. NTLM (v1) uses super weak cryptographic algorithms (DES and MD5), which makes it a bad choice even when disregarding the other reasons. We are slowly deprecating NTLM in curl, but we are starting out by making it opt-in. Starting in curl 8.20.0, NTLM is disabled by default in the build unless specifically enabled. Microsoft themselves have deprecated NTLM already. The wget project looks like it is about to make their NTLM support opt-in. curl only supports SMB version 1. This protocol uses NTLM for the authentication and it is equally bad in this protocol. Without NTLM enabled in the build, SMB support will also get disabled. But also: SMBv1 is in itself a weak protocol that is barely used by curl users, so this protocol is also opt-in starting in curl 8.20.0. You need to explicitly enable it in the build to get it added. I want to emphasize that we have not removed support for these ancient protocols, we just strongly discourage using them and I believe this is a first step down the ladder that in a future will make them get removed completely.

Security DevOps Open Source

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daniel.haxx.se 3 months ago

bye bye RTMP

In May 2010 we merged support for the RTMP protocol suite into curl, in our desire to support the world’s internet transfer protocols. The protocol is an example of the spirit of an earlier web: back when we still thought we would have different transfer protocols for different purposes. Before HTTP(S) truly became the one protocol that rules them all. RTMP was done by Adobe, used by Flash applications etc. Remember those? RTMP is an ugly proprietary protocol that simply was never used much in Open Source. The common Open Source implementation of this protocol is done in the rtmpdump project . In that project they produce a library, librtmp , which curl has been using all these years to handle the actual binary bits over the wire. Build curl to use librtmp and it can transfer RTMP:// URLs for you. In our constant pursuit to improve curl, to find spots that are badly tested and to identify areas that could be weak from a security and functionality stand-point, our support of RTMP was singled out. Here I would like to stress that I’m not suggesting that this is the only area in need of attention or improvement, but this was one of them. As I looked into the RTMP situation I realized that we had no (zero!) tests of our own that actually verify RTMP with curl. It could thus easily break when we refactor things. Something we do quite regularly. I mean refactor (but also breaking things). I then took a look upstream into the librtmp code and associated project to investigate what exactly we are leaning on here. What we implicitly tell our users they can use. I quickly discovered that the librtmp project does not have a single test either. They don’t even do releases since many years back, which means that most Linux distros have packaged up their code straight from their repositories. (The project insists that there is nothing to release, which seems contradictory.) Is there perhaps any librtmp tests perhaps in the pipe? There had not been a single commit done in the project within the last twelve months and when I asked one of their leading team members about the situation, I was made clear to me that there is no tests in the pipe for the foreseeable future either. In November 2025 I explicitly asked for RTMP users on the curl-library mailing list, and one person spoke up who uses it for testing. In the 2025 user survey, 2.2% of the respondents said they had used RTMP within the last year. The combination of few users and untested code is a recipe for pending removal from curl unless someone steps up and improves the situation. We therefor announced that we would remove RTMP support six months into the future unless someone cried out and stepped up to improve the RTMP situation. We repeated this we-are-doing-to-drop-RTMP message in every release note and release video done since then, to make sure we do our best to reach out to anyone actually still using RTMP and caring about it. If anyone would come out of the shadows now and beg for its return, we can always discuss it – but that will of course require work and adding test cases before it would be considered. Can we remove support for a protocol and still claim API and ABI backwards compatibility with a clean conscience? This is the first time in modern days we remove support for a URL scheme and we do this without bumping the SONAME. We do not consider this an incompatibility primarily because no one will notice . It is only a break if it actually breaks something. (RTMP in curl actually could be done using six separate URL schemes, all of which are no longer supported: rtmp rtmpe rtmps, rtmpt rtmpte rtmpts.) The offical number of URL schemes supported by curl is now down to 27: DICT, FILE, FTP, FTPS, GOPHER, GOPHERS, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, MQTT, MQTTS, POP3, POP3S, RTSP, SCP, SFTP, SMB, SMBS, SMTP, SMTPS, TELNET, TFTP, WS and WSS. The commit that actually removed RTMP support has been merged. We had the protocol supported for almost sixteen years. The first curl release without RTMP support will be 8.20.0 planned to ship on April 29, 2026

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daniel.haxx.se 3 months ago

One hundred curl graphs

In the spring of 2020 I decided to finally do something about the lack of visualizations for how the curl project is performing, development wise. How does the line of code growth look like? How many command line options have we had over time and how many people have done more than 10 commits per year over time? I wanted to have something that visually would show me how the project is doing, from different angles, viewpoints and probes. In my mind it would be something like a complicated medical device monitoring a patient that a competent doctor could take a glance at and assess the state of the patient’s health and welfare. This patient is curl, and the doctors would be fellow developers like myself. GitHub offers some rudimentary graphs but I found (and still find) them far too limited. We also ran gitstats on the repository so there were some basic graphs to get ideas from. I did a look-around to see what existing frameworks and setups that existed that I should base this one, as I was convinced I would have to do quite some customizing myself. Nothing I saw was close enough to what I was looking for. I decided to make my own, at least for a start. I decided to generate static images for this, not add some JavaScript framework that I don’t know how to use to the website. Static daily images are excellent for both load speed and CDN caching. As we already deny running JavaScript on the site that saved me from having to work against that. SVG images are still vector based and should scale nicely. SVG is also a better format from a download size perspective, as PNG almost always generate much larger images for this kind of images. When this started, I imagined that it would be a small number of graphs mostly showing timelines with plots growing from lower left to upper right. It would turn out to be a little naive. I knew some basics about gnuplot from before as I had seen images and graphs generated by others in the past. Since gitstats already used it I decided to just dive in deeper and use this. To learn it. gnuplot is a 40 year old (!) command line tool that can generate advanced graphs and data visualizations. It is a powerful tool, which also means that not everything is simple to understand and use at once, but there is almost nothing in terms of graphs, plots and curves that it cannot handle in one way or another. I happened to meet Lee Phillips online who graciously gave me a PDF version of his book aptly named gnuplot . That really helped! I decided that for every graph I want to generate, I first gather and format the data with one script, then render an image in a separate independent step using gnuplot. It made it easy to work on them in separate steps and also subsequently tune them individually and to make it easy to view the data behind every graph if I ever think there’s a problem in one etc. It took me about about two weeks of on and off working in the background to get a first set of graphs visualizing curl development status. I then created the glue scripting necessary to add a first dashboard with the existing graphs to the curl website. Static HTML showing static SVG images. On March 20, 2020 the first version of the dashboard showed no less than twenty separate graphs. I refer to “a graph” as a separate image, possibly showing more than one plot/line/curve. That first dashboard version had twenty graphs using 23 individual plots. Since then, we display daily updated graphs there . All data used for populating the graphs is open and available, and I happily use whatever is available: Open and transparent as always. Every once in a while since then I get to think of something else in the project, the code, development, the git history, community, emails etc that could be fun or interesting to visualize and I add a graph or two more to the dashboard. Six years after its creation, the initial twenty images have grown to one hundred graphs including almost 300 individual plots. Most of them show something relevant, while a few of them are in the more silly and fun category. It’s a mix. The 100th graph was added on March 15, 2026 when I brought back the “vulnerable releases” graph (appearing on the site on March 16 for the first time). It shows the number of known vulnerabilities each past release has. I removed it previously because it became unreadable, but in this new edition I made it only show the label for every 4th release which makes it slightly less crowded than otherwise. vulnerabilities in releases This day we also introduce a new 8-column display mode. Many of the graphs are internal and curl specific of course. The scripts for this, and the entire dashboard, remain written specifically for curl and curl’s circumstances and data. They would need some massaging and tweaking in order to work for someone else. All the scripts are of course open and available for everyone. I used to also offer all the CSV files generated to render the graphs in an easy accessible form on the site, but this turned out to be work done for virtually no audience, so I removed that again. If you replace the .svg extension with .csv, you can still get most of the data – if you know. The graphs and illustrations are not only silly and fun. They also help us see development from different angles and views, and they help us draw conclusions or at least try to. As an established and old project that makes an effort to do right, some of what we learn from this curl data might be possible to learn from and use even in other projects. Maybe even use as basis when we decide what to do next. I personally have used these graphs in countless blog posts, Mastodon threads and public curl presentations. They help communicate curl development progress. On Mastodon I keep joking about me being a graphaholic and often when I have presented yet another graph added the collection, someone has asked the almost mandatory question: how about a graph over number of graphs on the dashboard? Early on I wrote up such a script as well, to immediately fulfill that request. On March 14 2026, I decided to add it it as a permanent graph on the dashboard. Graphs in the curl dashboard The next-level joke (although some would argue that this is not fun anymore) is then to ask me for a graph showing the number of graphs for graphs. As I aim to please, I have that as well. Although this is not on the dashboard: Number of graphs on the dashboard showing number of graphs on the dashboard More graphs I am certain I (we?) will add more graphs over time. If you have good ideas for what source code or development details we should and could illustrate, please let me know. The git repository: https://github.com/curl/stats/ Daily updated curl dashboard: https://curl.se/dashboard.html curl gitstats: https://curl.se/gitstats/ git repository (source, tags, etc) GitHub issues mailing list archives curl vulnerability data hackerone reports historic details from the curl past

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