{"id":"CVE-2026-9679","aliases":["GHSA-p88m-4jfj-68fv"],"url":"https://o3.security/vulnerability/CVE-2026-9679","summary":"undici vulnerable to HTTP header injection via Set-Cookie percent-decoding","details":"## Impact\n\nundici's cookie parser in `parseSetCookie` percent-decodes cookie values via `qsUnescape`, turning encoded sequences like `%0D%0A`, `%00`, `%3B`, and `%3D` into their literal byte equivalents. RFC 6265 §5.4 does not specify any decoding and browsers do not decode either.\n\nApplications that parse a `Set-Cookie` header and then forward the parsed value into a response header (proxies, middleware, SSR frameworks) become vulnerable to HTTP response header injection: an attacker-controlled upstream can inject arbitrary `Set-Cookie`, `Location`, or `Cache-Control` headers into the application's downstream response, enabling session fixation, open redirect, or cache poisoning.\n\nAffected applications are those that use undici's cookie parsing (`parseSetCookie`, `parseCookie`, `getSetCookies`) and forward the parsed cookie value into a response header.\n\nThis was introduced in undici 7.0.0 via [#3789](https://github.com/nodejs/undici/pull/3789).\n\n## Patches\n\nUpgrade to undici v6.27.0, v7.28.0 or v8.5.0.\n\n## Workarounds\n\nIf upgrade is not immediately possible, do not forward values returned by `parseSetCookie`/`parseCookie`/`getSetCookies` directly into response headers; sanitize the value first to strip or reject CR, LF, NUL, `;`, and `=` bytes.","published":"2026-06-17T16:56:18.579Z","modified":"2026-10-21T02:30:46.749264670Z","cvss":{"score":5.9,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N"},"epss":{"score":0.00257,"percentile":0.17618,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"undici","fixedVersion":"6.27.0"},{"ecosystem":"npm","name":"undici","fixedVersion":"7.28.0"},{"ecosystem":"npm","name":"undici","fixedVersion":"8.5.0"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://cna.openjsf.org/security-advisories.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/9xxx/CVE-2026-9679.json"},{"type":"ADVISORY","url":"https://github.com/nodejs/undici/security/advisories/GHSA-p88m-4jfj-68fv"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-9679"},{"type":"PACKAGE","url":"https://github.com/nodejs/undici"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T02:30:46.749264670Z"}}