{"id":"CVE-2026-11525","state":"PUBLISHED","title":"undici vulnerable to Set-Cookie SameSite attribute downgrade via permissive substring matching","description":"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.","publishedAt":"2026-06-17T17:31:03.163Z","updatedAt":"2026-06-17T17:54:22.022Z","severity":{"score":3.7,"label":"Low","version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N","source":"openjs"},"assigner":"openjs","products":["undici undici"],"affected":[{"vendor":"undici","product":"undici","packageURL":"pkg:npm/undici","defaultStatus":"unaffected","versions":[{"version":"0","status":"affected","lessThan":"6.26.0","versionType":"semver"},{"version":"6.26.0","status":"unaffected","versionType":"semver"},{"version":"7.0.0","status":"affected","lessThan":"7.28.0","versionType":"semver"},{"version":"7.28.0","status":"unaffected","versionType":"semver"},{"version":"8.0.0","status":"affected","lessThan":"8.5.0","versionType":"semver"},{"version":"8.5.0","status":"unaffected","versionType":"semver"}]}],"references":["https://github.com/nodejs/undici/security/advisories/GHSA-g8m3-5g58-fq7m","https://cna.openjsf.org/security-advisories.html"],"weaknesses":["CWE-183"],"ingestedAt":"2026-10-29T20:10:52.580Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/11xxx/CVE-2026-11525.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-11525","state":"PUBLISHED","datePublished":"2026-06-17T17:31:03.163Z","dateUpdated":"2026-06-17T17:54:22.022Z","assignerShortName":"openjs","assignerOrgId":"ce714d77-add3-4f53-aff5-83d477b104bb","dateReserved":"2026-06-07T18:49:35.986Z"},"containers":{"cna":{"title":"undici vulnerable to Set-Cookie SameSite attribute downgrade via permissive substring matching","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"undici","product":"undici","packageURL":"pkg:npm/undici","defaultStatus":"unaffected","versions":[{"version":"0","status":"affected","lessThan":"6.26.0","versionType":"semver"},{"version":"6.26.0","status":"unaffected","versionType":"semver"},{"version":"7.0.0","status":"affected","lessThan":"7.28.0","versionType":"semver"},{"version":"7.28.0","status":"unaffected","versionType":"semver"},{"version":"8.0.0","status":"affected","lessThan":"8.5.0","versionType":"semver"},{"version":"8.5.0","status":"unaffected","versionType":"semver"}]}],"references":[{"url":"https://github.com/nodejs/undici/security/advisories/GHSA-g8m3-5g58-fq7m"},{"url":"https://cna.openjsf.org/security-advisories.html"}],"metrics":[{"format":"CVSS","cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N","baseScore":3.7,"baseSeverity":"LOW"},"scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-183","lang":"en","description":"CWE-183: Permissive List of Allowed Inputs","type":"CWE"}]}],"providerMetadata":{"shortName":"openjs","orgId":"ce714d77-add3-4f53-aff5-83d477b104bb","dateUpdated":"2026-06-17T17:31:03.163Z"},"credits":[{"lang":"en","type":"remediation reviewer","value":"UlisesGascon"},{"lang":"en","type":"remediation reviewer","value":"KhafraDev"},{"lang":"en","type":"remediation developer","value":"mcollina"},{"lang":"en","type":"reporter","value":"tndud042713"}],"x_generator":{"engine":"cve-kit 1.0.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-06-17T17:53:40.763762Z","id":"CVE-2026-11525","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-06-17T17:54:22.022Z"}}]}}}