HTTP header injection via Set-Cookie percent-decoding
Published Jun 17, 2026 · Updated Jun 17, 2026
HTTP header injection in Node.js Undici before 6.27.0, 7.0.0 through 7.27.0, and 8.0.0 through 8.4.0 allows remote attackers to alter responses. The parseSetCookie path calls qsUnescape on cookie values, converting percent-encoded CR, LF, NUL, semicolon, and equals bytes into literal delimiters interpreted during downstream header construction. Exploitation requires an application to parse a Set-Cookie header from an attacker-controlled upstream and forward the decoded value into a response header, enabling injected cookies, redirects, or cache directives.
Summary
What happened
HTTP header injection in Node.js Undici before 6.27.0, 7.0.0 through 7.27.0, and 8.0.0 through 8.4.0 allows remote attackers to alter responses. The parseSetCookie path calls qsUnescape on cookie values, converting percent-encoded CR, LF, NUL, semicolon, and equals bytes into literal delimiters interpreted during downstream header construction. Exploitation requires an application to parse a Set-Cookie header from an attacker-controlled upstream and forward the decoded value into a response header, enabling injected cookies, redirects, or cache directives.
The record
- CVE
- CVE-2026-9679
- Published
- Jun 17, 2026
- Updated
- Jun 17, 2026
- Vendor
- Node.js
- Product
- Undici
- Classifications
- CWE-93, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jun 17, 2026CVE publishedPublication date reported by the CVE source.
- Jun 17, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0 <6.26.0
- Affected versionversion=7.0.0 <7.28.0
- Affected versionversion=8.0.0 <8.5.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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