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.
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Amazon_linux_2023 | — | Upgrade nodejs22-docsUpgrade nodejs22-debuginfoUpgrade v8-13.6-develUpgrade nodejs22Upgrade nodejs24-debugsourceUpgrade nodejs24-npmUpgrade nodejs24-debuginfoUpgrade nodejs22-full-i18nUpgrade nodejs24Upgrade nodejs22-libs-debuginfoUpgrade nodejs22-debugsourceUpgrade nodejs24-develUpgrade nodejs24-docsUpgrade v8-12.4-develUpgrade nodejs22-develUpgrade nodejs22-npmUpgrade nodejs22-libsUpgrade nodejs24-full-i18nUpgrade nodejs24-libs-debuginfoUpgrade nodejs24-libs | Jul 8, 2026 | Jun 17, 2026 |
| Redhat_linux | — | No solution exists | Jul 17, 2026 | Jun 17, 2026 |
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