CVE-2026-63349 AnyIO run_process/open_process ignores extra_groups and can retain parent supplementary groups
AnyIO subprocess helpers ignore extra_groups, allowing child processes to retain parent supplementary groups and bypass privilege dropping.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-63349?
CVE-2026-63349 is a high-severity vulnerability in agronholm anyio, published on 18 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
AnyIO is a high level asynchronous concurrency and networking framework that works on top of either Trio or asyncio. In 4.14.0, AnyIO accepts the POSIX extra_groups argument in anyio.run_process() and anyio.open_process(), but open_process() forwards the group argument to the backend instead of extra_groups. A caller that supplies extra_groups=[] to clear inherited supplementary groups can therefore launch a child that retains the parent process groups, undermining a privilege-dropping boundary. If group is also supplied, the integer group value is passed where an iterable of supplementary groups is expected and the launch can fail with TypeError. This issue affects POSIX applications that rely on AnyIO subprocess helpers to launch less-privileged child processes. This issue is fixed in version 4.14.2.
Which versions are affected by CVE-2026-63349?
3 open source packages ship an affected version, including anyio.
| Package | Affected | Fixed in |
|---|---|---|
anyio PyPI | From 4.14.0 | 4.14.2 |
anyio PyPI | From 4.14.0 | 4.14.2 |
anyio PyPI | From 4.14.0 | 4.14.2 |
How do I fix CVE-2026-63349?
Upgrade anyio to 4.14.2 or later.
Is CVE-2026-63349 being exploited?
There is no known exploitation of CVE-2026-63349 in the wild and no public exploit code.
Sources
Also known as CLEANSTART-2026-KA42623, DEBIAN-CVE-2026-63349, ECHO-5d39-da23-651e, GHSA-3w57-8xmc-8v26, MINI-29w7-xvw9-ccfj, MINI-2r7c-pm44-m9v2 and 17 more.