CVE-2026-63349
HighCVSS 7.0Summary
In AnyIO 4.14.0, open_process() forwards the group argument to the backend instead of extra_groups, despite accepting the extra_groups parameter. A call with extra_groups=[] to clear inherited supplementary groups can launch a child process that retains the parent's groups, weakening a privilege-dropping boundary. This affects POSIX applications using AnyIO subprocess helpers and is fixed in version 4.14.2.
Risk Assessment
A child process may retain the parent's group privileges, potentially enabling privilege escalation or access to resources that should be restricted. This impacts applications relying on AnyIO to launch less-privileged processes.
Recommendation
Upgrade AnyIO to version 4.14.2 or later. Review applications using extra_groups in AnyIO to ensure they do not depend on the flawed behavior.
Other vulnerabilities in AnyIO
See all- CVE-2026-63374Critical
AnyIO's TLS connections to internationalized (non-ASCII) domain names may be vulnerable if the connection is hijacked and redirected to a malicious server, potentially allowing man-in-the-middle attacks.
- CVE-2026-64847Medium
In AnyIO prior to 4.14.2, process-pool workers were started with stderr connected to a pipe the parent never drained. Worker code writing enough data to sys.stderr could fill the pipe and block before returning the response, causing the awaiting process-pool call to remain blocked indefinitely.
Original NVD description (English source)
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.