CVE-2026-9679

A flaw was found in undici. The cookie parser in the parseSetCookie function incorrectly decodes cookie values, which is contrary to standard specifications. This vulnerability allows an attacker-controlled upstream to inject arbitrary HTTP response headers, such as Set-Cookie, Location, or Cache-Control. The primary consequence is HTTP response header injection, which can lead to session fixation, open redirect, or cache poisoning.

Moderate: A flaw in the undici library's cookie parser can lead to HTTP response header injection. This occurs when applications, such as proxies or middleware, incorrectly forward percent-decoded cookie values from upstream into downstream response headers. Successful exploitation could result in session fixation, open redirects, or cache poisoning.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.