HAX CMS helps manage microsite universe with PHP or NodeJs backends. Prior to version 26.0.0, an OS command injection vulnerability exists in the Git.php library of the HAXcms PHP backend. The application constructs shell command strings using unsanitized input and executes them via proc_open(). An attacker who can control parameters passed into Git operations can execute arbitrary OS commands with the privileges of the web server. Out of 17 functions that invoke shell commands only 1 function ("commit()") correctly uses "escapeshellarg()". When combined with another vulnerability that allows configuration manipulation, this issue can lead to full remote code execution and complete system compromise. Version 26.0.0 patches the issue.