Set-Cookie attribute injection via unchecked cookie options
Published May 28, 2026 · Updated May 28, 2026
Header injection in Hono before 4.12.21 allows remote attackers to alter Set-Cookie attributes through user-controlled cookie options. The hono/cookie serialize() function appends runtime sameSite and priority values without rejecting semicolons, carriage returns, or line feeds because TypeScript literal constraints are not enforced at runtime. Exploitation requires an application to pass request-derived values into those options and a user to trigger that path; the result is cookie-attribute injection or, on permissive runtimes, a second Set-Cookie header.
Summary
What happened
Header injection in Hono before 4.12.21 allows remote attackers to alter Set-Cookie attributes through user-controlled cookie options. The hono/cookie serialize() function appends runtime sameSite and priority values without rejecting semicolons, carriage returns, or line feeds because TypeScript literal constraints are not enforced at runtime. Exploitation requires an application to pass request-derived values into those options and a user to trigger that path; the result is cookie-attribute injection or, on permissive runtimes, a second Set-Cookie header.
The record
- CVE
- CVE-2026-47675
- Published
- May 28, 2026
- Updated
- May 28, 2026
- Vendor
- Hono
- Product
- Hono
- Classifications
- CWE-113, CWE-1287, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- May 28, 2026CVE publishedPublication date reported by the CVE source.
- May 28, 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=< 4.12.21
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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