Craft CMS versions 5.10.0 through 5.10.12 contain an incomplete fix for CVE-2026-55794: the Controller::getPostedRedirectUrl() -> View::renderObjectTemplate() sink remained unsandboxed, and the same fix commit added a self-signing oracle in Cp::elementLabelHtml(). Because Craft/Yii HMAC tokens are not bound to a parameter name, an authenticated low-privilege control panel user with edit rights on a single element type can mint a token over attacker-controlled Twig for the returnUrl parameter and replay it as the redirect POST parameter, reaching the unsandboxed sink and achieving server-side template injection that executes arbitrary PHP code (full server compromise). The issue is fixed in 5.10.13.

Craft CMS versions 5.10.0 through 5.10.12 contain an incomplete fix for CVE-2026-55794: the Controller::getPostedRedirectUrl() -> View::renderObjectTemplate() sink remained unsandboxed, and the same fix commit added a self-signing oracle in Cp::elementLabelHtml(). Because Craft/Yii HMAC tokens are not bound to a parameter name, an authenticated low-privilege control panel user with edit rights on a single element type can mint a token over attacker-controlled Twig for the returnUrl parameter and replay it as the redirect POST parameter, reaching the unsandboxed sink and achieving server-side template injection that executes arbitrary PHP code (full server compromise). The issue is fixed in 5.10.13.