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Vulnerability · Published Sep 1, 2026 · Assigned by GitHub_M

CVE-2026-84368joi: Prototype pollution via a `__proto__` language key in custom messages

Low 3.7

In plain English

A low-severity prototype pollution in joi from hapijs. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 33% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)3.7Low
Exploit odds (30 days)0.4%top 66.8% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

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 packages & fixed versions

EcosystemPackageFixed inAdvisory
npm@hapi/joino fix listedGHSA-6w3j-5fw6-r9vr
npmjoi17.13.6GHSA-6w3j-5fw6-r9vr
npmjoi18.2.5GHSA-6w3j-5fw6-r9vr

Affected products (as reported)

VendorProductVersions
hapijs joi >= 16.0.0, <= 17.1.1>= 17.2.0, < 17.13.6>= 18.0.0, < 18.2.5

Weakness: CWE-1321 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

References