{"id":"CVE-2025-66456","aliases":["GHSA-hxj9-33pp-j2cc"],"url":"https://o3.security/vulnerability/CVE-2025-66456","summary":"Elysia vulnerable to prototype pollution with multiple standalone schema validation","details":"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.","published":"2025-12-09T19:43:10.252Z","modified":"2026-08-12T03:51:31.690445453Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"elysia","fixedVersion":"1.4.17"}],"fix":{"url":"https://github.com/elysiajs/elysia/commit/26935bf76ebc43b4a43d48b173fc853de43bb51e","label":"elysiajs/elysia@26935bf"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/66xxx/CVE-2025-66456.json"},{"type":"ADVISORY","url":"https://github.com/elysiajs/elysia/security/advisories/GHSA-8vch-m3f4-q8jf"},{"type":"ADVISORY","url":"https://github.com/elysiajs/elysia/security/advisories/GHSA-hxj9-33pp-j2cc"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-66456"},{"type":"FIX","url":"https://github.com/elysiajs/elysia/commit/26935bf76ebc43b4a43d48b173fc853de43bb51e"},{"type":"FIX","url":"https://github.com/elysiajs/elysia/commit/3af978663e437dccc6c1a2a3aff4b74e1574849e"},{"type":"FIX","url":"https://github.com/elysiajs/elysia/pull/1564"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:31.690445453Z"}}