AnyIO process-pool workers can block indefinitely on undrained stderr (CVE-2026-64847) | HOL Guard CVE

Medium · CVSS 0.0CVE-2026-64847GHSA-5P39-CFHJ-2XMP

AnyIO process-pool workers can block indefinitely on undrained stderr

Answer in brief

CVE-2026-64847 records a Medium severity (CVSS 0.0) vulnerability in AnyIO process-pool workers can block indefinitely on undrained stderr. The current sources do not mark it as known exploited. The current feed maps agronholm/anyio (generic), anyio (pip), anyio (pypi). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 18, 2026Updated Sep 18, 2026Source checked Sep 18, 2026First seen by HOL Sep 18, 2026Material review Sep 18, 2026

Upstream Advisory

Key facts

Risk: Medium · CVSS 0.0
Exploitation: Not marked as known exploited
Affected software: 3 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 0.0. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps agronholm/anyio (generic), anyio (pip), anyio (pypi). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
agronholm/anyiogeneric	< 4.14.2	Not reported
anyiopip	<4.14.2	4.14.2
anyiopypi	>=0 <4.14.2	4.14.2

Recommended response

Check inventory. Check lockfiles and deployed manifests for agronholm/anyio, anyio, anyio.
Review the reported fix. Update anyio to 4.14.2; anyio to 4.14.2 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 18, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 18, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 18, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.