CVE-2026-84367 hapijs CVE debrief

Who should care

Developers and administrators using the joi library in their applications, especially those with user-input data validation, should review and update their library versions to prevent potential prototype pollution attacks. This includes reviewing compensating controls for exposed systems while remediation is scheduled and verified, and checking relevant monitoring, detection, and logs for exposed assets that need extra review.

Technical summary

The joi library's lib/types/keys.js internals.rename() implementation used by object().rename() permits a schema that renames keys with a regular-expression source and a Joi.expression() or Joi.x() target that interpolates the pattern's own match data, combined with { multiple: true }, to derive a target from an attacker-controlled input key. An attacker can send x-__proto__ with an object value, causing the target to render as __proto__ and set the prototype of the object returned by validate() instead of creating an own key. Static-string targets and schemas using the default { multiple: false } are not affected.

Defensive priority

Review and update joi library versions to 17.13.5 or 18.2.4 to address potential prototype pollution vulnerability.

Recommended defensive actions

• Update joi library to version 17.13.5 or 18.2.4
• Review and validate input data to prevent prototype pollution
• Implement compensating controls to detect and prevent potential attacks
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed
• Check relevant monitoring, detection, and logs for exposed assets that need extra review

Evidence notes

Evidence from the NVD and CVE Program records indicate a prototype pollution vulnerability in joi library versions from 16.0.0 until 17.13.5 and 18.2.4. Limited information is available on exploitability and affected systems. The CVE record was published on 2026-09-01T21:18:47.737Z and has not been modified since then. The vulnerability affects the joi library's lib/types/keys.js internals.rename() implementation used by object().rename(). An attacker can send x-__proto__ with an object value, causing the target to render as __proto__ and set the prototype of the object returned by validate() instead of creating an own key. Developers and administrators using the joi library in their applications, especially those with user-input data validation, should review and update their library versions to prevent potential prototype pollution attacks.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.