CVE-2025-66456 — Prototype Pollution in Elysia

CWE-1321 — Prototype Pollution5 documents5 sources
Severity
9.1CRITICALNVD
EPSS
0.2%
top 57.93%
CISA KEV
Not in KEV
Exploit
No known exploits
Affected products
1
Elysiajs Elysia
Timeline
PublishedDec 9

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 …

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

Affected Packages3 packages

▶NVDelysiajs/elysia1.4.0 — 1.4.17
▶npmelysiajs/elysia1.4.0 — 1.4.17
▶CVEListV5elysiajs/elysia>= 1.4.0, < 1.4.17

Patches

Patch: github.com ↗Patch: github.com ↗Patch: github.com ↗

🔴Vulnerability Details

3
OSV
Elysia vulnerable to prototype pollution with multiple standalone schema validation↗2025-12-09
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CVEList
Elysia vulnerable to prototype pollution with multiple standalone schema validation↗2025-12-09
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GHSA
Elysia vulnerable to prototype pollution with multiple standalone schema validation↗2025-12-09
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🕵️Threat Intelligence

1
Wiz
CVE-2025-66456 Impact, Exploitability, and Mitigation Steps | Wiz↗
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CVE-2025-66456 — Prototype Pollution in Elysiajs Elysia | cvebase