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.

  • Published Sep 13, 2026
  • CVSS 6.3 medium
  • 0.4% chance of exploitation in the next 30 days (EPSS)
  • A fix is available

Affected software

CVE-2026-90771 at the National Vulnerability Database