FoF Pretty Mail 1.1.2 Command Injection Vulnerability

Exploit Title: FoF Pretty Mail 1.1.2 Extension for Flarum Command Injection
Exploit Author: Chokri Hammedi
Vendor Homepage: https://flarum.org/
Software Link: https://github.com/FriendsOfFlarum/pretty-mail
Version: 1.1.2
Tested on: Windows XP
CVE: N/A
Description:

The FoF Pretty Mail extension for Flarum is vulnerable to Command Injection
due to the unsafe handling of user input in the email template. An attacker
with administrative access can inject PHP code into the email template,
leading to arbitrary command execution on the server.

Steps to Reproduce:

Log in as an administrator on the Flarum forum.
Navigate to the FoF Pretty Mail extension settings.
Edit the email default template and insert one of the following payloads at
the end of the template:

<?php system('echo "Take The Rose"; id'); ?>
or
<?php system('echo "Take The Rose"; cat /etc/passwd'); ?>

Save the changes to the email template.
Trigger any action that sends an email, such as user registration or
password reset.
The recipient of the email will see the message "Take The Rose" followed by
the output of the injected command (id or cat /etc/passwd) in the email
content.