PYSEC-2026-4025

Vulnerability from pysec - Published: 2026-10-01 16:38 - Updated: 2026-10-01 17:10
VLAI
Details

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.

Severity
9.3 (Critical)
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
Impacted products
Name purl
anyio pkg:pypi/anyio
Aliases
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "anyio",
        "purl": "pkg:pypi/anyio"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "4.14.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.0.0",
        "1.0.0a1",
        "1.0.0a2",
        "1.0.0b1",
        "1.0.0b2",
        "1.0.0rc1",
        "1.0.0rc2",
        "1.1.0",
        "1.2.0",
        "1.2.1",
        "1.2.2",
        "1.2.3",
        "1.3.0",
        "1.3.1",
        "1.4.0",
        "2.0.0",
        "2.0.0b1",
        "2.0.0b2",
        "2.0.0rc1",
        "2.0.0rc2",
        "2.0.1",
        "2.0.2",
        "2.1.0",
        "2.2.0",
        "3.0.0",
        "3.0.0rc1",
        "3.0.0rc2",
        "3.0.0rc3",
        "3.0.0rc4",
        "3.0.1",
        "3.1.0",
        "3.2.0",
        "3.2.1",
        "3.3.0",
        "3.3.1",
        "3.3.2",
        "3.3.3",
        "3.3.4",
        "3.4.0",
        "3.5.0",
        "3.6.0",
        "3.6.1",
        "3.6.2",
        "3.7.0",
        "3.7.0rc1",
        "3.7.1",
        "4.0.0",
        "4.0.0rc1",
        "4.1.0",
        "4.10.0",
        "4.11.0",
        "4.12.0",
        "4.12.1",
        "4.13.0",
        "4.14.0",
        "4.14.1",
        "4.2.0",
        "4.3.0",
        "4.4.0",
        "4.5.0",
        "4.5.1",
        "4.5.2",
        "4.6.0",
        "4.6.1",
        "4.6.2",
        "4.6.2.post1",
        "4.7.0",
        "4.8.0",
        "4.9.0"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-63374",
    "GHSA-82r6-8w77-94w6"
  ],
  "details": "### Impact\nServices using internationalized (non-ASCII) domain names are potentially vulnerable to TLS connections made from AnyIO\u0027s `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\u0027s 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.",
  "id": "PYSEC-2026-4025",
  "modified": "2026-10-01T17:10:17.161568Z",
  "published": "2026-10-01T16:38:33.613922Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/agronholm/anyio/security/advisories/GHSA-82r6-8w77-94w6"
    },
    {
      "type": "WEB",
      "url": "https://github.com/agronholm/anyio/pull/1208"
    },
    {
      "type": "WEB",
      "url": "https://github.com/agronholm/anyio/commit/68f58915f82d9be8109ebbbd8f5d70577d43f2ce"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/agronholm/anyio"
    },
    {
      "type": "WEB",
      "url": "https://github.com/agronholm/anyio/releases/tag/4.14.2"
    },
    {
      "type": "PACKAGE",
      "url": "https://pypi.org/project/anyio"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-82r6-8w77-94w6"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-63374"
    }
  ],
  "severity": [
    {
      "score": "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "AnyIO: TLSStream IDNA 2003 host name encoding enables potential TLS certificate spoofing"
}



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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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