CVE-2025-66456

9.8 CRITICAL
Published: December 09, 2025 Modified: December 17, 2025

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.

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CVSS v3.x Details

0.0 Low Medium High Critical 10.0
Vector String
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

References to Advisories, Solutions, and Tools

Patch Vendor Advisory Exploit Third Party Advisory
https://github.com/elysiajs/elysia/pull/1564
Source: security-advisories@github.com
Issue Tracking Patch
https://github.com/elysiajs/elysia/security/advisories/GHSA-8vch-m3f4-q8jf
Source: security-advisories@github.com
Not Applicable
https://github.com/elysiajs/elysia/security/advisories/GHSA-hxj9-33pp-j2cc
Source: security-advisories@github.com
Exploit Patch Vendor Advisory
https://github.com/elysiajs/elysia/security/advisories/GHSA-8vch-m3f4-q8jf
Source: 134c704f-9b21-4f2e-91b3-4a467353bcc0
Not Applicable
https://github.com/elysiajs/elysia/security/advisories/GHSA-hxj9-33pp-j2cc
Source: 134c704f-9b21-4f2e-91b3-4a467353bcc0
Exploit Patch Vendor Advisory

7 reference(s) from NVD

Quick Stats

CVSS v3 Score
9.8 / 10.0
EPSS (Exploit Probability)
0.1%
23th percentile
Exploitation Status
Not in CISA KEV

Weaknesses (CWE)

Affected Vendors

elysiajs