Elysia vulnerable to prototype pollution with multiple standalone schema validation

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 }) }) ```

Source published

9 Dec 2025 17:11:53 UTC

Source modified

4 Feb 2026 03:31:17 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Publisher rating · CRITICAL