Server code execution via unescaped cookie config
Published Dec 9, 2025 · Updated Dec 12, 2025
Code injection in Elysia before 1.4.18 allows attackers with cookie-configuration write access to execute JavaScript in the server process. The composeHandler code interpolates cookie option strings into generated route source without escaping backticks or interpolation sequences. Exploitation requires AOT compilation, a cookie schema, and attacker-controlled configuration; chaining prototype pollution removes the direct write-access gate.
Summary
What happened
Code injection in Elysia before 1.4.18 allows attackers with cookie-configuration write access to execute JavaScript in the server process. The composeHandler code interpolates cookie option strings into generated route source without escaping backticks or interpolation sequences. Exploitation requires AOT compilation, a cookie schema, and attacker-controlled configuration; chaining prototype pollution removes the direct write-access gate.
The record
- CVE
- CVE-2025-66457
- Published
- Dec 9, 2025
- Updated
- Dec 12, 2025
- Vendor
- ElysiaJS
- Product
- Elysia
- Classifications
- CWE-94, CAPEC-242, T1059.007
- Attack vector
- network
- Privileges
- admin
Timeline
How it unfolded
- Dec 9, 2025CVE publishedPublication date reported by the CVE source.
- Dec 12, 2025Record 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=< 1.4.18
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
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
- Elysia cookie injection proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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