---
id: CVE-2025-66456
title: >-
  Elysia is a Typescript framework for request validation, type inference,
  OpenAPI documentation and client-server communication
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 result…
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-1321
vendor: elysiajs
product: elysia
affected:
  - 'elysia >= 1.4.0, < 1.4.17'
patched:
  - elysia 1.4.17
published: '2025-12-09'
updated: '2026-10-14'
sourceUpdated: '2026-10-14T21:10:00.183'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-66456'
references:
  - url: >-
      https://github.com/elysiajs/elysia/commit/26935bf76ebc43b4a43d48b173fc853de43bb51e
    label: security-advisories@github.com
  - url: >-
      https://github.com/elysiajs/elysia/commit/3af978663e437dccc6c1a2a3aff4b74e1574849e
    label: security-advisories@github.com
  - url: 'https://github.com/elysiajs/elysia/pull/1564'
    label: security-advisories@github.com
  - url: 'https://github.com/elysiajs/elysia/security/advisories/GHSA-8vch-m3f4-q8jf'
    label: security-advisories@github.com
  - url: 'https://github.com/elysiajs/elysia/security/advisories/GHSA-hxj9-33pp-j2cc'
    label: security-advisories@github.com
  - url: 'https://github.com/elysiajs/elysia/security/advisories/GHSA-8vch-m3f4-q8jf'
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
  - url: 'https://github.com/elysiajs/elysia/security/advisories/GHSA-hxj9-33pp-j2cc'
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
tags:
  - nvd
epss: 0.0056
epssPercentile: 0.45287
ingestedAt: '2026-10-14T21:57:04.770Z'
---

## Overview

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.

## Affected

- `elysia >= 1.4.0, < 1.4.17`

## Remediation

Upgrade past the affected range:

- `elysia 1.4.17`