Prototype Pollution in Hapijs Joi
CVE-2026-90771
joi before versions 17.13.8 and 18.2.9 contains a prototype pollution vulnerability in the messages compilation function that accepts __proto__ as an error code. Attackers can supply __proto__ keys in custom messages to replace the returned object's prototype, breaking downstream code relying on Object.prototype methods.
Vulnerability class: Prototype Pollution
CVSS v3 metric
CVSS v3 base score 3.7 (Low). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N.
Affected products
Weakness classification (CWE)
References
- disclosure@vulncheck.com (issue-tracking)
- disclosure@vulncheck.com (product)
- disclosure@vulncheck.com (technical-description)
- disclosure@vulncheck.com (patch)
- disclosure@vulncheck.com (third-party-advisory)
Frequently asked questions
- What is CVE-2026-90771?
- CVE-2026-90771 is a low-severity vulnerability in Hapijs Joi, classified under Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution). CVSS score: 3.7/10. Published 2026-09-13.
- How severe is CVE-2026-90771?
- Low severity. CVSS v3 base score is 3.7 out of 10.