The popular TBDev code on which thousands of private BitTorrent trackers are built, is said to be vulnerable to a major exploit. A successful attack could allow a malicious attacker to deface the main tracker page (index.php) and hijack the account of anyone who logs into the application. Worryingly it’s even possible to hijack an administrator’s account by using a social engineering attack to get them to click on specially crafted hyperlink, although most admins won’t be tricked by this method.
According to Michael Brooks, a security researcher who brought this issue to our attention, this particular TBDev exploit is down to the fact the developers didn’t protect the administrative interface from Cross Site Scripting attacks (XSS).
The attack uses CSRF in a chain with other flaws to obtain synergy – Michael calls this CSRF Bouncing.
“Unfortunately this Cross Site Scripting attack is accessible by an attacker using a Cross Site Request Forgery” Michael told TorrentFreak. “The Cross Site Scripting flaw is particularly valuable. The XSS payload is stored in the main index.php for the application. This means that an attacker can expose every visitor to their payload.”
Worryingly, even if the attacker doesn’t have a user account, it’s possible to get one using an XSS flaw.
Michael explained how a malicious attacker increases his chances of a success with the exploit, by combining it with a little social engineering.
“In this case I am using the reflective XSS flaw to make it appear as though the administrator is viewing his own web application. The social engineering attack could look something like this: ‘I think there is a bug in your site. Can you check this link, it just does not look right http://localhost/redir.php?url=’ . This now means the flaw is no longer a “Cross Site” Request Forgery, because the request is being sent from the same website.”
After a successful attack it’s possible to deface the site and “hijack every user’s authentication token indefinitely”.
So what can be done to avoid this exploit? Michael told TorrentFreak:
“The most important thing to keep in mind is do not click on links that look like this. The link can be easily modified to be shorter, but the important part is avoiding links to TBDev’s /redir.php.”
“However this isn’t the only way that the flaw can be exploited. If you visit a website that the hacker controls then he can also trigger the attack. If you think you might have clicked on a bad link, change your password immediately.”
So what should an admin do if they already fell victim to the exploit?
“To remove the persistent XSS payload the administrator might have to login to the SQL server manually and delete the offending entry in the “news” table (since they won’t be able to use the web application to delete the news posting) using DELETE FROM news WHERE body LIKE ‘%fromCharCode%’.
The difficult part is that every user will have to change their password. In PHP I suggest defending against XSS using htmlspecialchars($var,ENT_QUOTES); . There are cases where XSS can still be possible without ENT_QUOTES. To defend against CSRF i suggest using PHP CSRF Guard.”
An administrator on a TBDev tracker we spoke with suggested a very quick fix off the top of his head:
in news.php change
$body = $_POST[“body”];
$body = htmlspecialchars($_POST[“body”],ENT_QUOTES);
We put this to Michael who told us: “The fix isn’t bad however the same fix also needs to be applied to $_GET[“url”] in redir.php or the administrator account as well as others are subjected to hijack. There are other security problems with this application, but the XSS is the most serious as it leads to immediate attack.”
Earlier today TorrentFreak contacted a number of admins with details of the exploit. Michael tells us he has notified the relevant people of the flaw but it may take a few days until an official patch is made available.
The full details of the exploit are available here.