Executive brief
Craft CMS is a content management system that provides control panel functionality for managing website content. An authenticated attacker with low-privilege edit rights can exploit an incomplete security fix to execute arbitrary PHP code on the server, achieving full server compromise. The vulnerability stems from improper validation of template rendering functions that allow untrusted Twig code execution.
Technical details
This vulnerability is an incomplete fix for CVE-2026-55794 affecting the Controller::getPostedRedirectUrl() → View::renderObjectTemplate() code path, which remained unsandboxed. The same fix commit introduced a self-signing oracle in Cp::elementLabelHtml(). An authenticated low-privilege control panel user with edit rights on a single element type can forge an HMAC token over attacker-controlled Twig for the returnUrl parameter. Since Craft/Yii HMAC tokens are not bound to parameter names, the token can be replayed as the redirect POST parameter to reach the unsandboxed template rendering sink, resulting in server-side template injection (SSTI) that executes arbitrary PHP code. Attack vector is network-based, requiring prior authentication and element edit privileges. The vulnerability is fixed in version 5.10.13.
Affected products
- Craft CMS 5.10.0 through 5.10.12
Timeline
- 2026-09-16: disclosed
- 2026-09-16: patched: Fixed in version 5.10.13