{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 12.1.1"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "mitmproxy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "12.1.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-1395",
      "CWE-444"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2025-08-25T21:01:00Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "mitmproxy 12.1.1 and below embed python-hyper/h2 \u2264 v4.2.0, which has a gap in its HTTP/2 header validation. This enables request smuggling attacks when mitmproxy is in a configuration where it translates HTTP/2 to HTTP/1. For example, this affects reverse proxies to `http://` backends. It does not affect mitmproxy\u0027s regular mode.\n\nAll users are encouraged to upgrade to mitmproxy 12.1.2, which includes a fixed version of h2.\n\nMore details about the vulnerability itself can be found at https://github.com/python-hyper/h2/security/advisories/GHSA-847f-9342-265h.",
  "id": "GHSA-63cx-g855-hvv4",
  "modified": "2025-08-25T21:01:01Z",
  "published": "2025-08-25T21:01:00Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/mitmproxy/mitmproxy/security/advisories/GHSA-63cx-g855-hvv4"
    },
    {
      "type": "WEB",
      "url": "https://github.com/python-hyper/h2/security/advisories/GHSA-847f-9342-265h"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/mitmproxy/mitmproxy"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "mitmproxy binaries embed a vulnerable python-hyper/h2 dependency"
}