# AnyIO process-pool workers can block indefinitely on undrained stderr

Advisory record · `GHSA-5p39-cfhj-2xmp`

- **Identifiers:** `GHSA-5p39-cfhj-2xmp` · `CVE-2026-64847` · `PYSEC-2026-4024`
- **State:** Confirmed
- **Severity:** CVSS 6.8 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-770](https://cwe.mitre.org/data/definitions/770.html)
- **Tags:** [Denial of service](https://agentprime.io/advisories/tag/dos.md)
- **Published:** 18 Sept 2026
- **Updated:** 1 Oct 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 18 Sept 2026, 17:17 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `anyio` (PyPI): affected `<4.14.2`; fixed in `4.14.2`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> AnyIO versions before 4.14.2 are affected. Process-pool workers do not redirect stderr, so worker code that writes enough data to stderr can fill the pipe and block the awaiting process-pool call indefinitely. The source gives few details on who can trigger this beyond running untrusted or faulty code. Upgrade to anyio 4.14.2, which contains the fix.

Written 1 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 6.8 Medium, CVSS 4.0: `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`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0016, the 4th percentile, on 13 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:09 UTC: First seen by agentprime
- 31 Oct 2026, 14:09 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-5p39-cfhj-2xmp)

## Sources

- [GitHub Advisory Database: GHSA-5p39-cfhj-2xmp](https://github.com/advisories/GHSA-5p39-cfhj-2xmp)
- [OSV: GHSA-5p39-cfhj-2xmp](https://osv.dev/vulnerability/GHSA-5p39-cfhj-2xmp)
- <https://github.com/agronholm/anyio/security/advisories/GHSA-5p39-cfhj-2xmp>
- <https://github.com/agronholm/anyio/pull/1207>
- <https://github.com/agronholm/anyio/commit/f1b7301c8264b0d2e8d24a5788fd29e93dea4040>
- <https://github.com/agronholm/anyio>
- <https://github.com/agronholm/anyio/releases/tag/4.14.2>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-5p39-cfhj-2xmp>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-5p39-cfhj-2xmp/>. Everything for agents: <https://agentprime.io/llms.txt>.