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:
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
})
})Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | elysia | >= 1.4.0, < 1.4.17 | 1.4.17 |
References
- https://github.com/elysiajs/elysia/security/advisories/GHSA-8vch-m3f4-q8jf
- https://github.com/elysiajs/elysia/security/advisories/GHSA-hxj9-33pp-j2cc
- https://nvd.nist.gov/vuln/detail/CVE-2025-66456
- https://github.com/elysiajs/elysia/pull/1564
- https://github.com/elysiajs/elysia/commit/26935bf76ebc43b4a43d48b173fc853de43bb51e
- https://github.com/elysiajs/elysia/commit/3af978663e437dccc6c1a2a3aff4b74e1574849e
- https://github.com/elysiajs/elysia
- https://github.com/sportshead/elysia-poc
- CVSS vector
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- Weakness (CWE)
CWE-1321- Platform
- npm
- Package
elysia- Disclosed
- 09.12.2025
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-hxj9-33pp-j2cc - CC BY 4.0
Vulnerability history: elysia
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 5
- First → latest
- 12.2025 09.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 1
- High 3
- Medium 1
Disclosures per year
- 2025: 2
- 2026: 3
-
Elysia vulnerable to prototype pollution with multiple standalone schema validation this entry
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