Sanitize Inputs in PHP

1) Function for stripping out malicious bits

<?php
function cleanInput($input) {
 
  $search = array(
    '@@si',   // Strip out javascript
    '@<[\/\!]*?[^<>]*?>@si',            // Strip out HTML tags
    '@@siU',    // Strip style tags properly
    '@<![\s\S]*?--[ \t\n\r]*>@'         // Strip multi-line comments
  );
 
    $output = preg_replace($search, '', $input);
    return $output;
  }
?>

2) Sanitization function

Uses the function above, as well as adds slashes as to not screw up database functions.

<?php
function sanitize($input) {
    if (is_array($input)) {
        foreach($input as $var=>$val) {
            $output[$var] = sanitize($val);
        }
    }
    else {
        if (get_magic_quotes_gpc()) {
            $input = stripslashes($input);
        }
        $input  = cleanInput($input);
        $output = mysql_real_escape_string($input);
    }
    return $output;
}
?>

Usage

<?php
  $bad_string = "Hi! <script src='http://www.evilsite.com/bad_script.js'>< /script> It's a good day!";
  $good_string = sanitize($bad_string);

  $_POST = sanitize($_POST);
  $_GET  = sanitize($_GET);
?>

Reference URL