Server-side Template Injection (SSTI) in grav

Grav is a file-based Web-platform built in PHP. Grav is subject to a server side template injection (SSTI) vulnerability. The fix for another SSTI vulnerability using |map, |filter and |reduce twigs implemented in the commit 71bbed1 introduces bypass of the denylist due to incorrect return value from isDangerousFunction(), which allows to execute the payload prepending double backslash (\\). The isDangerousFunction() check in version 1.7.42 and onwards retuns false value instead of true when the \ symbol is found in the $name. This vulnerability can be exploited if the attacker has access to: 1. an Administrator account, or 2. a non-administrator, user account that has Admin panel access and Create/Update page permissions. A fix for this vulnerability has been introduced in commit b4c6210 and is included in release version 1.7.42.2. Users are advised to upgrade. There are no known workarounds for this vulnerability.