CVE-2026-84367 joi: object().rename() with a template target can set the validated object's prototype

What is CVE-2026-84367?

CVE-2026-84367 is a low-severity vulnerability in hapijs joi, published on 1 Sep 2026.

Official description

joi is a schema description language and data validator for JavaScript. From 16.0.0 until 17.13.5 and 18.2.4, joi'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. The global Object.prototype is not modified, so the effect is confined to the object returned by that validation call. Static-string targets and schemas using the default { multiple: false } are not affected. This issue is fixed in versions 17.13.5 and 18.2.4.

Weakness: CWE-1321

Which versions are affected by CVE-2026-84367?

4 open source packages ship an affected version, including joi.

How do I fix CVE-2026-84367?

Upgrade joi to a fixed version for your release line: 17.13.5 or 18.2.4.

Is CVE-2026-84367 being exploited?

There is no known exploitation of CVE-2026-84367 in the wild and no public exploit code.

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as ECHO-b209-69fa-da03, GHSA-gg4h-3hg2-grpc, MINI-22wm-q4g5-j4pm, MINI-3hfp-4hhv-qqph, MINI-55hx-429w-7f6c, MINI-6p98-336j-pp7h and 15 more.