SSI Injection (Server-side Include) is a server-side exploit technique that allows an attacker to send code into a web application, which will later be executed locally by the web server. SSI Injection exploits a web application’s failure to sanitize user-supplied data before they are inserted into a server-side interpreted HTML file.

Before serving an HTML web page, a web server may parse and execute Server-side Include statements before providing it to the user. In some cases (e.g. message boards, guest books, or content management systems), a web application will insert user-supplied data into the source of a web page.

If an attacker submits a Server-side Include statement, he may have the ability to execute arbitrary operating system commands, or include a restricted file’s contents the next time the page is served.