Vulnerability · Published Sep 18, 2026 · Assigned by GitHub_M
CVE-2026-64847AnyIO process-pool workers can block indefinitely on undrained stderr
Medium 6.8
In plain English
A medium-severity resource allocation without limits in anyio from agronholm. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 5% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
AnyIO is a high level asynchronous concurrency and networking framework that works on top of either Trio or asyncio. Prior to 4.14.2, AnyIO starts process-pool workers with standard error connected to a pipe that the parent never drains, even though the documented behavior redirects all three standard streams. Worker code that writes enough attacker-influenced data to sys.stderr can fill the pipe and block before returning the standard-output protocol response, causing the awaiting process-pool call to remain blocked indefinitely. Applications that run untrusted or faulty worker code capable of producing substantial standard-error output are affected. This issue is fixed in version 4.14.2.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | python-anyio | no fix listed | DEBIAN-CVE-2026-64847 |
| Debian:13 | python-anyio | no fix listed | DEBIAN-CVE-2026-64847 |
| Debian:14 | python-anyio | 4.15.1-1 | DEBIAN-CVE-2026-64847 |
| PyPI | anyio | 4.14.2 | GHSA-5p39-cfhj-2xmp |
| PyPI | anyio | 4.14.2 | PYSEC-2026-4024 |
| Ubuntu:22.04:LTS | python-anyio | no fix listed | UBUNTU-CVE-2026-64847 |
| Ubuntu:24.04:LTS | python-anyio | no fix listed | UBUNTU-CVE-2026-64847 |
| Ubuntu:26.04:LTS | python-anyio | no fix listed | UBUNTU-CVE-2026-64847 |
| Ubuntu:26.10 | python-anyio | no fix listed | UBUNTU-CVE-2026-64847 |
Affected products (as reported)
Weakness: CWE-770 · Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
References
- https://github.com/agronholm/anyio/security/advisories/GHSA-5p39-cfhj-2xmp x_refsource_CONFIRM
- https://github.com/agronholm/anyio/pull/1207 x_refsource_MISC
- https://github.com/agronholm/anyio/commit/f1b7301c8264b0d2e8d24a5788fd29e93dea4040 x_refsource_MISC
- https://github.com/agronholm/anyio/releases/tag/4.14.2 x_refsource_MISC