---
id: CVE-2026-64847
title: >-
  AnyIO is a high level asynchronous concurrency and networking framework that
  works on top of either Trio or asyncio
summary: >-
  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,…
severity: medium
cvss: 6.8
cvssVector: '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'
cwe:
  - CWE-770
vendor: agronholm
product: anyio
affected:
  - anyio < 4.14.2
patched:
  - anyio 4.14.2
published: '2026-09-18'
updated: '2026-09-18'
sourceUpdated: '2026-09-18T18:17:10.930'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-64847'
references:
  - url: >-
      https://github.com/agronholm/anyio/commit/f1b7301c8264b0d2e8d24a5788fd29e93dea4040
    label: security-advisories@github.com
  - url: 'https://github.com/agronholm/anyio/pull/1207'
    label: security-advisories@github.com
  - url: 'https://github.com/agronholm/anyio/releases/tag/4.14.2'
    label: security-advisories@github.com
  - url: 'https://github.com/agronholm/anyio/security/advisories/GHSA-5p39-cfhj-2xmp'
    label: security-advisories@github.com
  - url: 'https://github.com/advisories/GHSA-5p39-cfhj-2xmp'
  - url: 'https://github.com/agronholm/anyio'
tags:
  - nvd
  - cve.org
  - ghsa
  - pip
  - osv
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-09-18T18:07:19.030895Z'
cvssSource: cna
aliases:
  - GHSA-5p39-cfhj-2xmp
ecosystem: pip
ingestedAt: '2026-09-18T17:46:41.530Z'
epss: 0.00121
epssPercentile: 0.02219
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Package advisory (CVE-2026-64847)

Affected packages:

- `anyio < 4.14.2`

Patched in:

- `anyio 4.14.2`

Source: https://github.com/advisories/GHSA-5p39-cfhj-2xmp