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.
History

Wed, 23 Sep 2026 00:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-1322
References
Metrics threat_severity

None

cvssV3_1

{'score': 5.5, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}

threat_severity

Moderate


Mon, 21 Sep 2026 10:45:00 +0000

Type Values Removed Values Added
First Time appeared Agronholm
Agronholm anyio
Vendors & Products Agronholm
Agronholm anyio

Fri, 18 Sep 2026 21:30:00 +0000

Type Values Removed Values Added
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.
Title AnyIO process-pool workers can block indefinitely on undrained stderr
Weaknesses CWE-770
References
Metrics cvssV4_0

{'score': 6.8, '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'}

ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published: 2026-09-18T17:04:32.038Z

Updated: 2026-09-18T18:07:27.772Z

Reserved: 2026-07-20T18:31:39.290Z

Link: CVE-2026-64847

cve-icon Vulnrichment

Updated: 2026-09-18T18:07:23.520Z

cve-icon NVD

Status : Deferred

Published: 2026-09-18T18:17:10.930

Modified: 2026-09-24T21:25:27.050

Link: CVE-2026-64847

cve-icon Redhat

Severity : Moderate

Publid Date: 2026-09-18T17:04:32Z

Links: CVE-2026-64847 - Bugzilla