Grav is a flat-file content management system. Versions prior to 1.7.42 are vulnerable to server side template injection. Remote code execution is possible by embedding malicious PHP code on the administrator screen by a user with page editing privileges. Version 1.7.42 contains a fix for this issue.
https://github.com/getgrav/grav/security/advisories/GHSA-f9jf-4cp4-4fq5
https://github.com/getgrav/grav/commit/9d01140a63c77075ef09b26ef57cf186138151a5