elysiajs elysia up to 1.4.26 prototype pollution

Summaryinfo

A vulnerability was found in elysiajs elysia up to 1.4.26 and classified as critical. This affects an unknown part. The manipulation results in prototype pollution. This vulnerability is cataloged as CVE-2026-31865. The attack may be launched remotely. There is no exploit available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in elysiajs elysia up to 1.4.26. It has been classified as critical. Affected is an unknown code. The manipulation with an unknown input leads to a prototype pollution vulnerability. CWE is classifying the issue as CWE-1321. The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

Elysia is a Typescript framework for request validation, type inference, OpenAPI documentation, and client-server communication. Prior to version 1.4.27, an Elysia cookie can be overridden by prototype pollution , eg. `__proto__`. This issue is patched in 1.4.27. As a workaround, use t.Cookie validation to enforce validation value and/or prevent iterable over cookie if possible.

The advisory is available at github.com. This vulnerability is traded as CVE-2026-31865 since 03/09/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. The technical details are unknown and an exploit is not available. This vulnerability is assigned to T1059 by the MITRE ATT&CK project.

Upgrading to version 1.4.27 eliminates this vulnerability. Applying the patch e9d6b1743fa7368ef942dce181f6a089757f6aab is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-12749). If you want to get best quality of vulnerability data, you may have to visit VulDB.

Productinfo

Vendor

• elysiajs

Name

• elysia

Version

• 1.4.0
• 1.4.1
• 1.4.2
• 1.4.3
• 1.4.4
• 1.4.5
• 1.4.6
• 1.4.7
• 1.4.8
• 1.4.9
• 1.4.10
• 1.4.11
• 1.4.12
• 1.4.13
• 1.4.14
• 1.4.15
• 1.4.16
• 1.4.17
• 1.4.18
• 1.4.19
• 1.4.20
• 1.4.21
• 1.4.22
• 1.4.23
• 1.4.24
• 1.4.25
• 1.4.26

License

• open-source

Website

• Product: https://github.com/elysiajs/elysia/

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Entryinfo

If you want to get best quality of vulnerability data, you may have to visit VulDB.

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