What is "suexec"

Apache suEXEC is a feature of the Apache Web server. It allows users to run CGI and SSI applications as a different user - normally, all web server processes run as the default web server user (often wwwrun, www-data, Apache or nobody). The suEXEC feature consists of a module for the web server and a binary executable which acts as a wrapper. suEXEC was introduced in Apache 1.2 and is often included in the default Apache package provided by most Linux distributions.

If a client requests a CGI and suEXEC is activated, it will call the suEXEC binary which then wraps the CGI scripts and executes it under the user account of the server process (virtual host) defined in the virtual host directive.

Additionally, suEXEC perform a multi-step check on the executed CGI to ensure security for the server (including path-checks, a limit of permitted commands, etc.)