curl 8.16.0

Welcome to one of the more feature-packed curl releases we have had in a while. Exactly eight weeks since we shipped 8.15.0.

Release presentation

Numbers

the 270th release
17 changes
56 days (total: 10,036)
260 bugfixes (total: 12,538)
453 commits (total: 36,025)
2 new public libcurl function (total: 98)
0 new curl_easy_setopt() option (total: 308)
3 new curl command line option (total: 272)
76 contributors, 39 new (total: 3,499)
32 authors, 17 new (total: 1,410)
2 security fixes (total: 169)

Security

We publish two severity-low vulnerabilities in sync with this release:

  • CVE-2025-9086 identifies a bug in the cookie path handler that can make curl get confused and override a secure cookie with a non-secure one using the same name. If the planets all happen to align correctly.
  • CVE-2025-10148 points out a mistake in the WebSocket implementation that makes curl not update the frame mask correctly for each new outgoing frame – as it is supposed to.

Changes

We have a long range of changes this time:

  • curl gets a --follow option
  • curl gets an --out-null option
  • curl gets a --parallel-max-host option to limit concurrent connections per host
  • --retry-delay and --retry-max-time accept decimal seconds
  • curl gets support for --longopt=value
  • curl -w now supports %time{}
  • now libcurl caches negative name resolves
  • ip happy eyeballing: keep attempts running
  • bump minimum mbedtls version required to 3.2.0
  • add curl_multi_get_offt() for getting multi related information
  • add CURLMOPT_NETWORK_CHANGED to signal network changed to libcurl
  • use the NETRC environment variable (first) if set
  • bump minimum required mingw-w64 to v3.0 (from v1.0)
  • smtp: allow suffix behind a mail address for RFC 3461
  • make default TLS version be minimum 1.2
  • drop support for msh3
  • support CURLOPT_READFUNCTION for WebSocket

Bugfixes

The official bugfix count surpassed 250 this cycle and we have documented them all in the changelog, including links to most issues or pull-requests where they originated.

See the release presentation for a walk-through of some of the perhaps most interesting ones.

preparing for the worst

One of these mantras I keep repeating is how we in the curl project keep improving, keep polishing and keep tightening every bolt there is. No one can do everything right from day one, but given time and will we can over time get a lot of things lined up in neat and tidy lines.

And yet new things creep up all the time that can be improved and taken yet a little further.

An exercise

Back in the spring of 2025 we had an exercise at our curl up meeting in Prague. Jim Fuller played up an imaginary life-like scenario for a bunch of curl maintainers. In this role played major incident we got to consider how we would behave and what we would do in the curl project if something like Heartbleed or a serious breach occur.

It was a little of an eye opener for several of us. We realized we should probably get some more details written down and planned for.

Plan ahead

We of course arrange for things and work on procedures and practices to the best of our abilities to make sure that there will never be any such major incident in the curl project. However, as we are all human and we all do mistakes, it would be foolish to think that we are somehow immune against incidents of the highest possible severity level. Rationally, we should just accept the fact that even though the risk is ideally really slim, it exists. It could happen.

What if the big bad happens

We have now documented some guidelines about what exactly constitutes a major incident, how it is declared, some roles we need to shoulder while it is ongoing, with a focus on both internal and external communication, and how we declare that the incident has ended. It’s straight forward and quite simple.

Feel free to criticize or improve those if you find omissions or mistakes. I imagine that if we ever get to actually use these documented steps because of such a project-shaking event, we will get reasons to improve it. Until then we just need to apply our imagination and make sure it seems reasonable.

giants, standing on the shoulders of

This was the title of my keynote at the Open Source Summit Europe 2025 conference in Amsterdam that I delivered on August 25, 2025.

The giants, as in fact large parts of modern infrastructure, stand on the shoulders of Open Source projects and their maintainers. But maybe these projects and people are not treated in optimal ways.

The slides are available.

My slot allowed me 15 minutes and I completed my presentation with around two minutes left. I have rarely received so many positive comments as after this talk.

Credits

The painting in the top image, The Colossus (also known as The Giant), is traditionally attributed to Francisco de Goya but might actually have been made by his friend Asensio Juliá.