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GHSA-hxj9-33pp-j2cc

CriticalCVSS 9.1 / 10
Published Dec 9, 2025·Last modified Feb 4, 2026
Affected Components(0)

No affected components available

Description

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:

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

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
			})
	})
Risk Scores
Base Score
9.1

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability.

Threat Intelligence
6.9

Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.

EPSS
0.70%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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