CVE-2025-66456

Critical

Published: 09/12/2025(UTC)Translated: 05/08/2026(UTC)NVD NIST

Summary

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.

Risk Assessment

An attacker can exploit the vulnerability to achieve remote code execution, leading to full server compromise and data breach.

Recommendation

Update Elysia to version 1.4.17 or later. As a temporary workaround, remove the __proto__ key from request bodies.

Original NVD description (English source)

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.