{"id":"CVE-2026-63374","aliases":["GHSA-82r6-8w77-94w6","PYSEC-2026-4025"],"url":"https://o3.security/vulnerability/CVE-2026-63374","summary":"AnyIO: TLSStream IDNA 2003 host name encoding enables potential TLS certificate spoofing","details":"### Impact\nServices 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.\n\n### Patches\nThe vulnerability will be patched in v4.14.2.\n\n### Workarounds\nEncode host names via the `idna` package prior to connecting.","published":"2026-09-22T15:23:14.259Z","modified":"2026-10-29T12:27:02.216338539Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"PyPI","name":"anyio","fixedVersion":"4.14.2"}],"fix":{"url":"https://github.com/agronholm/anyio/commit/68f58915f82d9be8109ebbbd8f5d70577d43f2ce","label":"agronholm/anyio@68f5891"},"references":[{"type":"WEB","url":"https://github.com/agronholm/anyio/releases/tag/4.14.2"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63374.json"},{"type":"ADVISORY","url":"https://github.com/agronholm/anyio/security/advisories/GHSA-82r6-8w77-94w6"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-63374"},{"type":"FIX","url":"https://github.com/agronholm/anyio/commit/68f58915f82d9be8109ebbbd8f5d70577d43f2ce"},{"type":"FIX","url":"https://github.com/agronholm/anyio/pull/1208"},{"type":"PACKAGE","url":"https://github.com/agronholm/anyio"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-29T12:27:02.216338539Z"}}