Open Redirect
CVE-2026-9679
MEDIUM
Severity by source
AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
Primary rating from Vendor (openjs) · only source for this CVE.
CVSS VectorVendor: openjs
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
Lifecycle Timeline
1DescriptionCVE.org
Impact: undici'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.
Applications 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.
Affected applications are those that use undici's cookie parsing (parseSetCookie, parseCookie, getSetCookies) and forward the parsed cookie value into a response header.
This was introduced in undici 7.0.0 via PR #3789.
Patches: Upgrade to undici v6.26.0, v7.28.0 or v8.5.0.
Workarounds: If 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.
AnalysisAI
HTTP response header injection in undici's cookie parser exposes proxy, middleware, and SSR framework applications to session fixation, open redirect, and cache poisoning. The parseSetCookie, parseCookie, and getSetCookies functions incorrectly percent-decode cookie values using qsUnescape, converting encoded sequences such as %0D%0A into literal CRLF bytes in violation of RFC 6265 §5.4, which prescribes no such decoding. …
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