CVE-2025-66456
published 2025-12-09CVE-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…
PriorityP357critical9.8CVSS 3.1
AVNACLPRNUINSUCHIHAH
EPSS
0.47%
37.4th percentile
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
3 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| elysiajs | elysia | — | — |
| elysiajs | elysia | >= 1.4.0 < 1.4.17 | 1.4.17 |
| elysiajs | elysia | >= 1.4.0 < 1.4.17 | 1.4.17 |
CVSS provenance
nvdv3.19.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
nvdv4.09.1CRITICALCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
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OSV
Elysia vulnerable to prototype pollution with multiple standalone schema validation
osv·2025-12-09
CVE-2025-66456 [CRITICAL] Elysia vulnerable to prototype pollution with multiple standalone schema validation
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:
GHSA
Elysia vulnerable to prototype pollution with multiple standalone schema validation
ghsa·2025-12-09
CVE-2025-66456 [CRITICAL] CWE-1321 Elysia vulnerable to prototype pollution with multiple standalone schema validation
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:
No detection rules found.
No public exploits indexed.
https://github.com/elysiajs/elysia/commit/26935bf76ebc43b4a43d48b173fc853de43bb51ehttps://github.com/elysiajs/elysia/commit/3af978663e437dccc6c1a2a3aff4b74e1574849ehttps://github.com/elysiajs/elysia/pull/1564https://github.com/elysiajs/elysia/security/advisories/GHSA-8vch-m3f4-q8jfhttps://github.com/elysiajs/elysia/security/advisories/GHSA-hxj9-33pp-j2cchttps://github.com/elysiajs/elysia/security/advisories/GHSA-8vch-m3f4-q8jfhttps://github.com/elysiajs/elysia/security/advisories/GHSA-hxj9-33pp-j2cc
2025-12-09
Published