CVE-2026-84368: Hapijs Joi

Low severity, CVSS 3.7. EPSS: 0.4% chance of exploitation in the next 30 days.

joi is a schema description language and data validator for JavaScript. From 16.0.0 until 17.13.6 and 18.2.5, the @hapi/joi package through 17.1.1 and the successor joi package contain prototype pollution in lib/messages.js, where exports.compile() and exports.merge() reuse inherited objects for attacker-controlled language keys supplied through messages(), message(), prefs({ messages }), Joi.extend({ messages }), or rule({ message }). A language key named __proto__ writes properties onto Object.prototype, and constructor writes to the Object function's static properties. A consuming application that gates on the presence of an inherited property can take the wrong branch for every inspected object. The flaw is not reachable from data that joi validates and requires an application to feed untrusted input directly into schema-construction configuration. This issue is fixed in joi versions 17.13.6 and 18.2.5; no fixed @hapi/joi version is available.

Affected products

• Hapijs Joi: from 16.0.0, up to and including 17.1.1; from 17.2.0, before 17.13.6 (fixed in 17.13.6); from 18.0.0, before 18.2.5 (fixed in 18.2.5)

Published 2026-09-01. Last modified 2026-09-09.