CVE-2025-66456
9.8 · CRITICALOverview
CVE-2025-66456 is a critical-severity vulnerability affecting elysiajs elysia. It was published on December 9, 2025 and has a CVSS 3.1 base score of 9.8 (CRITICAL).
This vulnerability has a CVSS 3.1 base score of 9.8, rated CRITICAL. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
Technical Description
Elysia is a Typescript framework for request validation, type inference, OpenAPI documentation and client-server communication. Versions 1.4.0 through 1.4.16 contain a prototype pollution vulnerability in `mergeDeep` after merging results of two standard schema validations with the same key. Due to the ordering of merging, there must be an any type that is set as a standalone guard, to allow for the `__proto__ prop` to be merged. When combined with GHSA-8vch-m3f4-q8jf this allows for a full RCE by an attacker. This issue is fixed in version 1.4.17. To workaround, remove the `__proto__ key` from body.
Remediation
Check the references section for vendor advisories and patches from elysiajs. Update elysia to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
Affected Products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| elysiajs | elysia | >= 1.4.0, < 1.4.17 | Affected |
References
Frequently Asked Questions
What is CVE-2025-66456?
CVE-2025-66456 is a critical-severity vulnerability affecting elysiajs elysia. It was published on December 9, 2025 and has a CVSS 3.1 base score of 9.8 (CRITICAL).
How severe is CVE-2025-66456?
This vulnerability has a CVSS 3.1 base score of 9.8, rated CRITICAL. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
How do I fix or remediate CVE-2025-66456?
Check the references section for vendor advisories and patches from elysiajs. Update elysia to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
How can CyberStrike help with CVE-2025-66456?
CyberStrike's AI-powered security agents can automatically detect CVE-2025-66456 across your infrastructure using autonomous pentesting, DAST scanning, and HackBrowser. The platform continuously monitors for known vulnerabilities and provides actionable remediation guidance prioritized by real-world exploitability.
How CyberStrike Helps
AI agents map your attack surface to find vulnerabilities like this one.
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