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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-63374
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-22 16:17:50 UTC
Updated2026-09-22 16:17:50 UTC
DescriptionAnyIO is a high level asynchronous concurrency and networking framework that works on top of either Trio or asyncio. Prior to 4.14.2, connect_tcp() and TLSStream.wrap() can validate internationalized host names after the standard library converts them with IDNA 2003 instead of IDNA 2008. When a connection to a non-ASCII domain is hijacked or redirected, an attacker can obtain a legitimate certificate for the different ASCII hostname produced by IDNA 2003 and present it to the client, causing the malicious endpoint's certificate to validate. This issue is fixed in version 4.14.2.

Risk And Classification

Primary CVSS: v4.0 9.3 CRITICAL from [email protected]

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Problem Types: CWE-295 | CWE-297 | CWE-295 CWE-295: Improper Certificate Validation | CWE-297 CWE-297: Improper Validation of Certificate with Host Mismatch

VersionSourceTypeScoreSeverityVector
4.0[email protected]Secondary9.3CRITICALCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/C...
4.0CNADECLARED9.3CRITICALCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
None
User Interaction
None
Confidentiality
High
Integrity
High
Availability
None
Sub Conf.
None
Sub Integrity
None
Sub Availability
None

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Agronholm Anyio affected < 4.14.2 Not specified

References

ReferenceSourceLinkTags
github.com/agronholm/anyio/releases/tag/4.14.2 [email protected] github.com
github.com/agronholm/anyio/security/advisories/GHSA-82r6-8w77-94w6 [email protected] github.com
github.com/agronholm/anyio/pull/1208 [email protected] github.com
github.com/agronholm/anyio/commit/68f58915f82d9be8109ebbbd8f5d70577d43f2ce [email protected] github.com
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