Describe CVE-2019-9859.
What is CVE-2019-9859?
Vesta Control Panel (VestaCP) 0.9.7 through 0.9.8-23 is vulnerable to an authenticated command execution that can result in remote root access on the server. The platform works with PHP as the frontend language and uses shell scripts to execute system actions. PHP executes shell script through the dangerous command exec. This function can be dangerous if arguments passed to it are not filtered. Every user input in VestaCP that is used as an argument is filtered with the escapeshellarg function. This function comes from the PHP library directly and its description is as follows: "escapeshellarg() adds single quotes around a string and quotes/escapes any existing single quotes allowing you to pass a string directly to a shell function and having it be treated as a single safe argument." It means that if you give Username, it will have 'Username' as a replacement. This works well and protects users from exploiting this potentially dangerous exec function. Unfortunately, VestaCP uses this escapeshellarg function incorrectly in several places..