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
Published · last modified .
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.
EPSS exploit prediction
EPSS: 0.004 (32.8th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 33rd percentile — 32.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: 0.000
Affected products
Weakness classification (CWE)
References
- github.com/hapijs/joi/issues/3150 (issue-tracking)
- github.com/hapijs/joi (product)
- github.com/hapijs/joi/blob/v18.2.8/lib/messages.js (technical-description)
- github.com/hapijs/joi/commit/5b8333c9177e08b4ef4ed02903c2d657084e7afb (patch)
- www.vulncheck.com/advisories/joi-before-17.13.8-and-18.2.9-prototype-pollution-… (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.