Thelia 3.0.0's back-office Email/Messages feature contains a server‑side template injection (SSTI) flaw that allows any authenticated user with the “Messages” permission to supply unsandboxed Twig templates, which are then compiled and executed as raw code. By modifying Message content, an attacker can execute arbitrary PHP functions, read sensitive files, and potentially write to the filesystem, leading to full compromise of the application and underlying host. This vulnerability has been patched in thelia/twig-engine-module 1.0.9.