CVE-2025-66456 — CRITICAL (9.8)

Q: How severe is CVE-2025-66456?

CVE-2025-66456 has been rated CRITICAL with a CVSS base score of 9.8/10. This is considered a critical vulnerability requiring immediate attention.

Q: Is there a patch for CVE-2025-66456?

Check the references section above for vendor advisories and patch information. Affected products include: Elysiajs Elysia.

Vulnerability 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.

CVSS Score

9.8

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

NONE

Scope

UNCHANGED

Confidentiality

HIGH

Integrity

HIGH

Availability

HIGH

Affected Products

Vendor	Product	Versions
Elysiajs	Elysia	>= 1.4.0, < 1.4.17

Related Weaknesses (CWE)

CWE-1321

References

https://github.com/elysiajs/elysia/commit/26935bf76ebc43b4a43d48b173fc853de43bb5Patch
https://github.com/elysiajs/elysia/commit/3af978663e437dccc6c1a2a3aff4b74e157484Patch
https://github.com/elysiajs/elysia/pull/1564Issue TrackingPatch
https://github.com/elysiajs/elysia/security/advisories/GHSA-8vch-m3f4-q8jfNot Applicable
https://github.com/elysiajs/elysia/security/advisories/GHSA-hxj9-33pp-j2ccExploitPatchVendor Advisory
https://github.com/elysiajs/elysia/security/advisories/GHSA-8vch-m3f4-q8jfNot Applicable
https://github.com/elysiajs/elysia/security/advisories/GHSA-hxj9-33pp-j2ccExploitPatchVendor Advisory

FAQ

What is CVE-2025-66456?

CVE-2025-66456 is a vulnerability with a CVSS score of 9.8 (CRITICAL). 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 vulnerabilit...

How severe is CVE-2025-66456?

CVE-2025-66456 has been rated CRITICAL with a CVSS base score of 9.8/10. This is considered a critical vulnerability requiring immediate attention.

Is there a patch for CVE-2025-66456?

Check the references section above for vendor advisories and patch information. Affected products include: Elysiajs Elysia.