CVE-2026-9679
MediumCVSS 5.9Exploitation Probability (EPSS)
Low risk17th percentile — higher than 17% of all known CVEs
Summary
Undici's cookie parser (parseSetCookie) decodes cookie values, which can lead to HTTP response header injection. Applications that forward parsed cookie values into response headers become vulnerable to attacks such as session fixation or malicious redirects.
Risk Assessment
Organizations may be exposed to attacks that allow the injection of malicious headers into HTTP responses, potentially leading to serious security breaches like session theft.
Recommendation
It is recommended to upgrade to undici v6.26.0, v7.28.0, or v8.5.0. If an upgrade is not immediately possible, sanitize values returned by parseSetCookie/parseCookie/getSetCookies before forwarding them to response headers.
Original NVD description (English source)
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.