Server Side Template Injection (SSTI) via Twig escape handler

Summary Due to the unrestricted access to twig extension class from grav context, an attacker can redefine the escape function and execute arbitrary commands. Details https://github.com/twigphp/Twig/blob/3.x/src/Extension/EscaperExtension.phpL99 php / Defines a new escaper to be used via the esca...