EUVD-2026-262992

fkie_cve-2025-66456

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.

GHSA-hxj9-33pp-j2cc — Elysia vulnerable to prototype pollution with multiple standalone schema validation

Affected: npm: elysia

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.

### Impact Routes with more than 2 standalone schema validation, eg. zod

Example vulnerable code: ```typescript import { Elysia } from "elysia" import * as z from "zod"

const app = new Elysia() .guard({ schema: "standalone", body: z.object({ data: z.any() }) }) .post("/", ({ body }) => ({ body, win: {}.foo }), { body: z.object({ data: z.object({ messageId: z.string("pollute-me"), }) }) }) ```

### Patches Patched by 1.4.17 (https://github.com/elysiajs/elysia/pull/1564)

Reference commit: - https://github.com/elysiajs/elysia/pull/1564/commits/26935bf76ebc43b4a43d48b173fc853de43bb51e - https://github.com/elysiajs/elysia/pull/1564/commits/3af978663e437dccc6c1a2a3aff4b74e1574849e

### Workarounds Remove `__proto__` key from body

Example plugin for removing `__proto__` from body

```typescript new Elysia() .onTransform(({ body, headers }) => { if (headers['content-type'] === 'application/json') return JSON.parse(JSON.stringify(body), (k, v) => { if (k === '__proto__') return

return v }) }) ```

Most recent entries from all

EUVD-2026-262992

fkie_cve-2025-66456

GHSA-hxj9-33pp-j2cc — Elysia vulnerable to prototype pollution with multiple standalone schema validation