CVE-2025-66456

Name: CVE-2025-66456
Creator: NVD / NIST
Published: 2025-12-09T20:15:54.76+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.1/10EPSS 0.47%

Last modified Jun 17, 2026

CVE-2025-66456 is a critical-severity vulnerability rated 9.1/10 on the CVSS scale. 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. EPSS estimates a 0.47% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

9.8/10

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

CVSS 4.0

9.1/10

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/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

EPSS Probability

0.47%

37.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-1321

Affected Software

Vendor	Product	Versions
Elysiajs	Elysia	>= 1.4.0, < 1.4.17

References

https://github.com/elysiajs/elysia/commit/26935bf76ebc43b4a43d48b173fc853de43bb51ePatch
https://github.com/elysiajs/elysia/commit/3af978663e437dccc6c1a2a3aff4b74e1574849ePatch
https://github.com/elysiajs/elysia/pull/1564Issue Tracking, Patch
https://github.com/elysiajs/elysia/security/advisories/GHSA-8vch-m3f4-q8jfNot Applicable
https://github.com/elysiajs/elysia/security/advisories/GHSA-hxj9-33pp-j2ccExploit, Patch, Vendor Advisory
https://github.com/elysiajs/elysia/security/advisories/GHSA-8vch-m3f4-q8jfNot Applicable
https://github.com/elysiajs/elysia/security/advisories/GHSA-hxj9-33pp-j2ccExploit, Patch, Vendor Advisory

Timeline

Published: Dec 9, 2025
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2025-66456?

How severe is CVE-2025-66456?

CVE-2025-66456 has a CVSS score of 9.1/10 (CRITICAL severity). The EPSS model estimates a 0.47% probability of exploitation in the next 30 days.

How do I fix CVE-2025-66456?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2025-66456?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST