# CVE-2026-90771

## Summary

- **CVE ID:** CVE-2026-90771
- **Severity:** MEDIUM
- **CVSS Score:** 6.3 (CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N)
- **CWE:** CWE-1321
- **Published:** Sep 13, 2026
- **Last Modified:** Sep 16, 2026

## Description

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.

## Affected Products

- hapijs — joi (16.0.0)
- hapijs — joi (18.0.0)

## References

- [CNA](https://github.com/hapijs/joi/issues/3150)
- [CNA](https://github.com/hapijs/joi)
- [CNA](https://github.com/hapijs/joi/blob/v18.2.8/lib/messages.js)
- [CNA](https://github.com/hapijs/joi/commit/5b8333c9177e08b4ef4ed02903c2d657084e7afb)
- [CNA](https://www.vulncheck.com/advisories/joi-before-17.13.8-and-18.2.9-prototype-pollution-via-messages)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.26%
- **EPSS Percentile:** 17.7

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._