joi: Prototype pollution via a `__proto__` language key in custom messages

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-84368
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-01 21:18:47 UTC
Updated2026-09-09 21:09:13 UTC
Descriptionjoi 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.

Risk And Classification

Primary CVSS: v3.1 3.7 LOW from [email protected]

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS: 0.002550000 probability, percentile 0.170980000 (date 2026-09-10)

Problem Types: CWE-1321 | CWE-1321 CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary3.7LOWCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
3.1CNADECLARED3.7LOWCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Hapijs Joi affected >= 16.0.0, <= 17.1.1 Not specified
CNA Hapijs Joi affected >= 17.2.0, < 17.13.6 Not specified
CNA Hapijs Joi affected >= 18.0.0, < 18.2.5 Not specified

References

ReferenceSourceLinkTags
github.com/hapijs/joi/security/advisories/GHSA-6w3j-5fw6-r9vr [email protected] github.com
github.com/hapijs/joi/pull/3139 [email protected] github.com
github.com/hapijs/joi/commit/8d0b808f3e874d28f9078f61b7742290989afb36 [email protected] github.com
github.com/hapijs/joi/pull/3138 [email protected] github.com
github.com/hapijs/joi/commit/90d07571923c90e3432a328fc041d1cda03d30fa [email protected] github.com
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