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Advisory record · GHSA-82r6-8w77-94w6

AnyIO: TLSStream IDNA 2003 host name encoding enables potential TLS certificate spoofing

CVSS 9.3 CriticalCriticalEPSS 0.0029 · 21st percentile

Critical, because:

  • CVSS score 9.3: 9.0 or more.

How we decide what’s critical

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.

PackageEcosystemAffectedFixed in
anyioPyPI<4.14.24.14.2
Identifiers
GHSA-82r6-8w77-94w6 · CVE-2026-63374 · PYSEC-2026-4025
Weakness (CWE)
CWE-295 · CWE-297
Tags
Published
18 Sept 2026
Updated
1 Oct 2026

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. When TLS connections are made with internationalized (non-ASCII) host names through connect_tcp() or TLSStream.wrap(), an attacker who has already redirected the connection to a malicious server can present a certificate issued for the IDNA 2003 form of the domain, which the client accepts. Upgrade to AnyIO 4.14.2. As a workaround, encode host names with the idna package before connecting.

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

ScoreRatingCVSSVectorSource
9.3 Critical 4.0 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N CNA (GitHub_M)
  • CISA KEV Not listed.
  • EPSS 0.0029, the 21st percentile, on 8 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 14:09 UTC First seen by agentprime
  2. 31 Oct 2026, 14:09 UTC Confirmed by OSV

Sources

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.