CVE-2026-63374
AnyIO: TLSStream IDNA 2003 host name encoding enables potential TLS certificate spoofing
Summary
### 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.
Affected packages
| Ecosystem | Package | Affected versions | Fixed versions |
|---|---|---|---|
| PyPI | anyio | — | 4.14.2 |
Remediation: Upgrade to 4.14.2 or later.
References
Includes data from the GitHub Advisory Database, licensed under CC-BY 4.0.
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