What are the potential security risks of allowing HTML in forum descriptions?

Allowing HTML in forum descriptions can pose security risks such as cross-site scripting (XSS) attacks, where malicious scripts can be injected into the forum and executed on users' browsers. To mitigate this risk, it is recommended to sanitize and validate any HTML input before displaying it on the forum page. This can be done by using functions like htmlspecialchars() to escape special characters and prevent script execution.

// Sanitize and validate HTML input before displaying in forum descriptions
$description = htmlspecialchars($_POST['description']);