disable_functions allows you to disable certain functions. It takes on a comma-delimited list of function names. These directives were used commonly to disable potentially unsafe functions from being used even if a malicious actor gets code-execution access in a server.
You can set this variable in the Platform, first log in to the Platform and select the website from the dashboard and then select either Upgrade PHP Version or PHP & Databases from the side menu.
Scroll down to the PHP Configuration section and click on Add Variable. Type disable_functions in the first box and enter the values for this variable in the Value box. For example, to disable exec and system you would enter "exec, system". Click Update Configuration to save your changes.