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CVE-2025-66456
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Date: December 9, 2025
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.
Severity Score
Related Resources (9)
Severity Score
Weakness Type (CWE)
Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
CWE-1321Top Fix
Upgrade Version
Upgrade to version elysia - 1.4.17;https://github.com/elysiajs/elysia.git - 1.4.17
CVSS v3.1
| Base Score: |
|
|---|---|
| Attack Vector (AV): | NETWORK |
| Attack Complexity (AC): | LOW |
| Privileges Required (PR): | NONE |
| User Interaction (UI): | NONE |
| Scope (S): | UNCHANGED |
| Confidentiality (C): | HIGH |
| Integrity (I): | HIGH |
| Availability (A): | HIGH |