hapijs Joi up to 17.13.8/18.3.0 Message Compilation lib/messages.js compile/merge prototype pollution

Summaryinfo

A vulnerability, which was classified as critical, has been found in hapijs Joi up to 17.13.8/18.3.0. This issue affects the function compile/merge of the file lib/messages.js of the component Message Compilation. This manipulation causes prototype pollution. This vulnerability is registered as CVE-2026-122131. Remote exploitation of the attack is possible. No exploit is available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in hapijs Joi up to 17.13.8/18.3.0. It has been declared as critical. Affected by this vulnerability is the function compile/merge of the file lib/messages.js of the component Message Compilation. The manipulation with an unknown input leads to a prototype pollution vulnerability. The CWE definition for the vulnerability is 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. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

Joi 17.13.6 before 17.13.9 and 18.2.5 before 18.3.1 contains a prototype pollution vulnerability in lib/messages.js compile() and merge() that fails to reject a __proto__ language key. Attackers supplying untrusted message configuration via any().messages(), prefs, validate options or Joi.extend can replace the compiled messages prototype, altering or breaking validation error rendering and dependent logic.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-122131 since 11/04/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1059 according to MITRE ATT&CK.

Upgrading to version 17.13.9 or 18.3.1 eliminates this vulnerability.

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Productinfo

Vendor

• hapijs

Name

• Joi

Version

• 17.13.0
• 17.13.1
• 17.13.2
• 17.13.3
• 17.13.4
• 17.13.5
• 17.13.6
• 17.13.7
• 17.13.8
• 18.0
• 18.1
• 18.2
• 18.3.0

Website

• Product: https://github.com/hapijs/joi/

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