{"api_version":"1","generated_at":"2026-06-23T17:09:00+00:00","cve":"CVE-2026-11525","urls":{"html":"https://cve.report/CVE-2026-11525","api":"https://cve.report/api/cve/CVE-2026-11525.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-11525","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-11525"},"summary":{"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. 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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.","state":"PUBLISHED","assigner":"openjs","published_at":"2026-06-17 18:17:35","updated_at":"2026-06-17 20:20:10"},"problem_types":["CWE-183","CWE-183 CWE-183: Permissive List of Allowed 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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."}],"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. 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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.","Type":"Description","Title":"undici vulnerable to Set-Cookie SameSite attribute downgrade via"}]}}}