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CVE-2026-63349 — anyio

Fix: agronholm/anyio@eb562e6

CVE-2026-63349 is a CWE-266 vulnerability in anyio. A fix is available for anyio — see the affected versions and patch details below.

AnyIO run_process/open_process ignores extra_groups and can retain parent supplementary groups

Also known asGHSA-3w57-8xmc-8v26PYSEC-2026-4023
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 1, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • A successful exploit gives an attacker total control of the affected component, not partial access.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-63349.

EPSS Exploitation Probability

via FIRST.org ↗
0.1%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs1th percentile — riskier than 1% of all scored CVEsHighest risk
0.00%0.20%0.41%0.61%0.1%0.1%Oct 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected
🐍anyio

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

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.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐍PyPIanyio≥ 4.14.0&&< 4.14.24.14.2pip install --upgrade 'anyio==4.14.2'

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for anyio, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update anyio to 4.14.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-63349 is resolved across your whole dependency graph.

  3. Workarounds

    Close the privilege gap rather than the entry point: audit which accounts, roles and service identities can reach the affected operation, drop the component to the least privilege it actually needs, and review file and directory permissions created by earlier installs — a default left in place is what makes this reachable.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

A MODERATE severity flaw was found in AnyIO, a Python asynchronous concurrency and networking library shipped in Red Hat products including Red Hat OpenStack Platform, Red Hat OpenShift AI, and Red Hat Satellite. On POSIX systems, anyio.run_process() and anyio.open_process() accept the extra_groups argument, but…

Workaround published by Red Hat
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability. The upstream project fixed this issue in AnyIO 4.14.2; updates for the affected Red Hat product streams are deferred because this flaw is rated MODERATE severity.
Source: Red Hat security advisory for CVE-2026-63349 (CC BY 4.0)

Frequently Asked Questions

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 gro
O3 Security · Impact-Aware SCA

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CVE-2026-63349: anyio — Fixed in 4.14.2