CVE-2026-9679
Description
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.
Statement
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.
Mitigation
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.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.9 | N/A | 5.9 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | High | N/A | High |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | High | N/A | High |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
cve.org: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Application Data
Frequently Asked Questions
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