Vulnerability · Published Nov 4, 2026 · Assigned by VulnCheck

CVE-2026-122131Joi 17.13.6 before 17.13.9 and 18.2.5 before 18.3.1 Prototype Replacement via proto Language Key

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 0.3% (higher than 26% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)3.7Low

Exploit odds (30 days)0.3%top 73.8% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
npm	@hapi/joi	no fix listed	GHSA-6w3j-5fw6-r9vr
npm	joi	17.13.6	GHSA-6w3j-5fw6-r9vr
npm	joi	18.2.5	GHSA-6w3j-5fw6-r9vr

Affected products (as reported)

Vendor	Product	Versions
hapijs	joi	17.13.6 – before 17.13.918.2.5 – before 18.3.1

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

References

Patch Commit patch
https://github.com/hapijs/joi product
https://github.com/hapijs/joi/commit/dae9467cec27e787bfdea8b276595177d52d28ec patch
https://github.com/hapijs/joi/pull/3164 patch, issue-tracking
GitHub Security Advisory (GHSA-6w3j-5fw6-r9vr) related, vendor-advisory
https://github.com/hapijs/joi/blob/v18.3.0/lib/messages.js#L64-L67 technical-description
VulnCheck Advisory: Joi 17.13.6 before 17.13.9 and 18.2.5 before 18.3.1 Prototype Replacement via __proto__ Language Key third-party-advisory