{"id":"CVE-2026-11525","summary":"undici vulnerable to Set-Cookie SameSite attribute downgrade via permissive substring matching","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.","aliases":["GHSA-g8m3-5g58-fq7m"],"modified":"2026-07-15T01:49:17.580347831Z","published":"2026-06-17T17:31:03.163Z","related":["ALSA-2026:35841","ALSA-2026:35842","ALSA-2026:35891","ALSA-2026:35892","CGA-2rp4-x4w5-v2x2","SUSE-SU-2026:22368-1","SUSE-SU-2026:2633-1","SUSE-SU-2026:2647-1","SUSE-SU-2026:2695-1","openSUSE-SU-2026:11121-1","openSUSE-SU-2026:21058-1","openSUSE-SU-2026:21236-1"],"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"},"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"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/nodejs/undici","events":[{"introduced":"0"},{"fixed":"551138cbc1742c92242a68216167761075e8a82c"},{"introduced":"1cfe0949053aac6267f11b919cee9315a27f1fd6"},{"fixed":"f9eba0ad9134e1c0977848476bba9d49734696e4"},{"introduced":"d7fbba51772deecb830a297647456a5e9f9fec57"},{"fixed":"a0806e1f66a83db0a792b8407c2e97fcf8ed58af"}],"database_specific":{"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","cpe":"cpe:2.3:a:nodejs:undici:*:*:*:*:*:node.js:*:*"}}],"versions":["v6.26.0","v7.27.2","v8.4.1","v8.4.0","v7.27.1","v7.27.0","v7.26.0","v6.25.0","v8.3.0","v8.2.0","v7.25.0","v7.24.8","v8.1.0","v8.0.3","v8.0.2","v8.0.1","v8.0.0","v7.24.7","v7.24.6","v7.24.5","v7.24.4","v7.24.3","v7.24.2","v6.24.1","v6.24.0","v7.24.1","v7.24.0","v6.23.0","v7.23.0","v7.22.0","v7.21.0","v7.20.0","v7.19.2","v7.19.1","v7.19.0","v7.18.2","v7.18.1","v7.18.0","v6.22.0","v7.17.0","v7.16.0","v7.15.0","v6.21.3","v7.14.0","v7.13.0","v7.12.0","v7.11.0","v7.10.0","v6.21.2","v7.9.0","v7.8.0","v7.7.0","v7.5.0","v7.6.0","v7.4.0","v6.21.1","v7.3.0","v7.2.3","v7.2.2","v7.2.1","v7.2.0","v7.1.1","v7.1.0","v7.0.0","v6.21.0","v6.20.1","v6.20.0","v6.19.8","v6.19.7","v6.19.6","v6.19.5","v6.19.4","v6.19.3","v6.19.2","v6.19.1","v6.19.0","v6.18.2","v6.18.1","v6.18.0","v6.17.0","v6.16.1","v6.16.0","v6.15.0","v6.14.1","v6.14.0","v6.13.0","v6.12.0","v6.11.1","v6.11.0","v6.10.2","v6.10.1","v6.10.0","v6.9.0","v6.8.0","v6.7.1","v6.7.0","v6.6.2","v6.6.1","v5.28.2","v6.6.0","v6.5.0","v6.4.0","v6.3.0","v6.2.1","v6.2.0","v6.1.0","v6.0.1","v6.0.0","v5.28.1","v5.28.0","v5.27.2","v5.27.1","v5.27.0","v5.26.5","v5.26.4","v5.26.3","v5.26.2","v5.26.1","v5.26.0","v5.23.4","v5.25.3","v5.25.2","v5.25.1","v5.25.0","v5.24.0","v5.23.0","v5.22.1","v5.22.0","v5.21.2","v5.21.1","v5.21.0","v5.20.0","v5.19.1","v5.19.0","v5.18.0","v5.17.1","v5.17.0","v5.16.0","v5.15.2","v5.15.1","v5.15.0","v5.14.0","v5.13.0","v5.12.0","v5.11.0","v5.10.0","v5.9.1","v5.8.2","v5.8.1","v5.8.0","v5.7.0","v5.6.1","v5.6.0","v5.5.1","v5.5.0","v5.4.0","v5.3.0","v5.2.0","v5.1.1","v5.1.0","v5.0.0","v4.16.0","v4.15.1","v4.15.0","v4.14.1","v4.14.0","v4.13.0","v4.12.2","v4.12.0","v4.11.3","v4.11.2","v4.11.1","v4.11.0","v4.10.4","v4.10.3","v4.10.2","v4.10.1","v4.10.0","v4.9.5","v4.9.4","v4.9.3","v4.9.2","v4.9.1","v4.9.0","v4.8.2","v4.8.1","v4.8.0","v4.7.3","v4.7.2","v4.7.1","v4.7.0","v4.6.0","v4.5.1","v4.5.0","v4.4.7","v4.4.6","v4.4.5","v4.4.4","v4.4.3","v4.4.2","v4.4.1","v4.3.1","v4.3.0","v4.2.2","v4.2.1","v4.1.1","v4.1.0","v4.0.0","v4.0.0-rc.8","v4.0.0-rc.7","v4.0.0-rc.5","v4.0.0-rc.4","v4.0.0-rc.3","v4.0.0-rc.2","v4.0.0-rc.1","v4.0.0-alpha.5","v4.0.0-alpha.4","v4.0.0-alpha.2","v4.0.0-alpha.1","v4.0.0-alpha.0","v3.3.1","v3.3.0","v3.2.0","v3.1.0","v3.0.0","v2.1.0","v2.0.7","v2.0.6","v2.0.5","v2.0.4","v2.0.3","v2.0.2","v2.0.1","v2.0.0","v1.3.1","v1.3.0","v1.2.6","v1.2.5","v1.2.2","v1.2.1","v1.2.0","v1.1.0","v1.0.3","v1.0.2","v1.0.1","v1.0.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-11525.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N"}]}