CVE•Published 2025-12-09•Modified 2026-10-14•1 article on news•5 live references•NVD data

CVE-2025-66456Elysiajs · Elysia

Vulnerability data via NVD (ingested)

CVSS v3.1

9.8

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS percentile

Exploit Prediction Scoring System · top 55% of all CVEs

Weaknesses (CWE)

CWE-1321Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')

Description

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.

Timeline

Published 2025-12-09

Modified 2026-10-14

External references

NVD MITRE Exploit-DB trickest/cve VulnCheck

Search for exposed instances

Shodan + Censys queries derived from NVD's CPE data. The vuln tag catches assets Shodan has explicitly linked to this CVE; the product / banner fingerprints find exposed instances even when the vuln tag was never applied (which is common).

Shodan · vuln tag0 hosts

vuln:CVE-2025-66456

Hosts Shodan has explicitly fingerprinted as vulnerable.

Shodan · product

product:"Elysiajs Elysia"

All exposed Elysiajs Elysia instances — cross-reference with the CVE's affected-version range.

Shodan · banner/body mention

http.html:"Elysia"

HTTP body or banner mentions "Elysia" — catches deploys Shodan didn't identify as a product.

More intel sources (5)

Shodan report

vuln:CVE-2025-66456