CVE-2026-31857: CraftCMS has an RCE vulnerability via relational conditionals in the control panel

A Remote Code Execution vulnerability exists in the Craft CMS 5 conditions system.

The BaseElementSelectConditionRule::getElementIds() method passes user-controlled string input through renderObjectTemplate() – an unsandboxed Twig rendering function with escaping disabled.

Any authenticated Control Panel user (including non-admin roles such as Author or Editor) can achieve full RCE by sending a crafted condition rule via standard element listing endpoints.

This vulnerability requires no admin privileges, no special permissions beyond basic control panel access, and bypasses all production hardening settings (allowAdminChanges: false, devMode: false, enableTwigSandbox: true).

Users should update to the patched 5.99 release to mitigate the issue.