{"cve":"CVE-2026-11525","nvd":{"published":"2026-06-17T18:17:35.097","modified":"2026-06-25T17:46:21.653","status":"Analyzed","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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N","score":3.7},"cwes":["CWE-183"],"references":["https://cna.openjsf.org/security-advisories.html","https://github.com/nodejs/undici/security/advisories/GHSA-g8m3-5g58-fq7m"],"products":["nodejs:undici"],"source":"nvd","synced_at":"2026-10-19T22:39:28.638635428+00:00"},"epss":{"cve":"CVE-2026-11525","score":0.00238,"percentile":0.14955,"date":"2026-11-01"},"kev":null,"osv":[{"id":"GHSA-g8m3-5g58-fq7m","url":"https://osv.dev/vulnerability/GHSA-g8m3-5g58-fq7m","summary":"undici vulnerable to Set-Cookie SameSite attribute downgrade via permissive substring matching","modified":"2026-09-10T03:51:08.663204806Z","packages":[{"ecosystem":"npm","name":"undici","purl":"pkg:npm/undici","ranges":["<6.27.0"],"fixed":["6.27.0"]},{"ecosystem":"npm","name":"undici","purl":"pkg:npm/undici","ranges":[">=7.0.0 <7.28.0"],"fixed":["7.28.0"]},{"ecosystem":"npm","name":"undici","purl":"pkg:npm/undici","ranges":[">=8.0.0 <8.5.0"],"fixed":["8.5.0"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}