Grav is a file-based Web platform. Prior to 1.8.0-beta.27, a Server-Side Template Injection (SSTI) vulnerability exists in Grav that allows authenticated attackers with editor permissions to execute arbitrary commands on the server and, under certain conditions, may also be exploited by unauthenticated attackers. This vulnerability stems from weak regex validation in the cleanDangerousTwig method. This vulnerability is fixed in 1.8.0-beta.27.

Affected: Packagist: getgrav/grav

### Summary A Server-Side Template Injection (SSTI) vulnerability exists in Grav that allows authenticated attackers with editor permissions to execute arbitrary commands on the server and, under certain conditions, may also be exploited by unauthenticated attackers. This vulnerability stems from weak regex validation in the `cleanDangerousTwig` method.

### Important - First of all this vulnerability is due to weak sanitization in the method `clearDangerousTwig`, so any other class that calls it indirectly through for example `$twig->processString` to sanitize code is also vulnerable.

- For this report, we will need the official Form and Admin plugin installed, also I will be chaining this with another vulnerability to allow an editor which is a user with only pages permissions to edit the process section of a form.

- I made another report for the other vulnerability which is a Broken Access Control which allows a user with full permission for pages to change the process section by intercepting the request and modifying it.

### Permissions Needed - The main case for this vulnerability is an editor which can unconditionally takeover the whole system through creating a vulnerable form. - Second case is as an unauthenticated user, so if the form exists already and accepts user input and puts it through `evaluate_twig`, a guest can takeover the system.

### Details When we make a form with a process section and a `message` action, when the form is submitted we get to deal wi…