{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "cpe": "cpe:2.3:a:nodejs:undici:*:*:*:*:*:node.js:*:*",
            "extracted_events": [
              {
                "introduced": "0"
              },
              {
                "fixed": "6.27.0"
              },
              {
                "introduced": "7.0.0"
              },
              {
                "fixed": "7.28.0"
              },
              {
                "introduced": "8.0.0"
              },
              {
                "fixed": "8.5.0"
              }
            ],
            "source": "CPE_RANGE"
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "551138cbc1742c92242a68216167761075e8a82c"
            },
            {
              "introduced": "1cfe0949053aac6267f11b919cee9315a27f1fd6"
            },
            {
              "fixed": "f9eba0ad9134e1c0977848476bba9d49734696e4"
            },
            {
              "introduced": "d7fbba51772deecb830a297647456a5e9f9fec57"
            },
            {
              "fixed": "a0806e1f66a83db0a792b8407c2e97fcf8ed58af"
            }
          ],
          "repo": "https://github.com/nodejs/undici",
          "type": "GIT"
        }
      ]
    }
  ],
  "aliases": [
    "GHSA-g8m3-5g58-fq7m"
  ],
  "database_specific": {
    "cna_assigner": "openjs",
    "cwe_ids": [
      "CWE-183"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/11xxx/CVE-2026-11525.json"
  },
  "details": "Impact:\nWhen undici parses a Set-Cookie header, it accepts any SameSite attribute value that contains Strict, Lax, or None as a substring, rather than the case-insensitive exact match specified by RFC 6265. Non-spec values are silently mapped to one of the three standard tokens. For example, SameSite=NoneOfYourBusiness is parsed as None (the most permissive setting), and SameSite=StrictLax is parsed as Lax (a downgrade from Strict).\n\nAffected applications are those that consume Set-Cookie headers from server responses (for example via undici's fetch or proxy code paths) and then forward or rely on the parsed sameSite attribute. A malicious or non-compliant server can coerce the consumer's view of a cookie's SameSite policy to a weaker value, silently degrading the SameSite enforcement the cookie is supposed to provide.\n\nThis was introduced in undici 5.15.0 when the cookies feature was added.\n\nPatches:\nUpgrade to undici v6.26.0, v7.28.0 or v8.5.0.\n\nWorkarounds:\nAfter parsing a Set-Cookie header, validate that the resulting sameSite attribute is one of 'Strict', 'Lax', or 'None' (exact, case-insensitive) before forwarding or relying on it.",
  "id": "CVE-2026-11525",
  "modified": "2026-07-15T01:49:17.580347831Z",
  "published": "2026-06-17T17:31:03.163Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://cna.openjsf.org/security-advisories.html"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/11xxx/CVE-2026-11525.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/nodejs/undici/security/advisories/GHSA-g8m3-5g58-fq7m"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-11525"
    }
  ],
  "schema_version": "1.8.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "undici vulnerable to Set-Cookie SameSite attribute downgrade via permissive substring matching"
}