AnyIO: TLSStream IDNA 2003 host name encoding enables potential TLS certificate spoofing
### Impact Services using internationalized (non-ASCII) domain names are potentially vulnerable to TLS connections made from AnyIO's `connect_tcp()` or directly via `TLSStream.wrap()` where the connection has (through other means) been hijacked and redirected to a malicious server. The attacker would obtain a legitimate certificate using the IDNA 2003 encoded version of the domain name and offer it to the connecting client, making the certificate validate properly on the client's end. ### Patches The vulnerability will be patched in v4.14.2. ### Workarounds Encode host names via the `idna` package prior to connecting.
describes (1)
Related CVEs.
| ID | severity | exploitable | ||
|---|---|---|---|---|
| CVE-2026-63374US | — | — | ||
AnyIO 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 validat… | ||||
references
External citations — patches, advisories, analysis.
- https://github.com/agronholm/anyioPACKAGE
- https://github.com/agronholm/anyio/commit/68f58915f82d9be8109ebbbd8f5d70577d43f2ceWEB
- https://github.com/agronholm/anyio/pull/1208WEB
- https://github.com/agronholm/anyio/releases/tag/4.14.2WEB
- https://github.com/agronholm/anyio/security/advisories/GHSA-82r6-8w77-94w6WEB
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