This script is vulnerable to PHP code injection.
PHP code injection is a vulnerability that allows an attacker to inject custom code into the server side scripting engine. This vulnerability occurs when an attacker can control all or part of an input string that is fed into an eval() function call. Eval will execute the argument as code.
An attacker can execute any PHP code on your server.
Your script should properly sanitize user input.
Dynamic Evaluation Vulnerabilities in PHP applications
OWASP PHP Top 5