How BitTorrent becomes a DDoS Tool [Hacking]

A talk at the 27C3 has revealed curtains off a new kind of swarms that can exploit DDoS attacks. 
One of the speakers at Chaos Communications Congress revealed how BitTorrent swarms can be exploited to take down large websites with relative ease under a talk named “Lying To The Neighbours” .

The vulnerability is actually found in the technology that works on trackerless torrents (DHT). Its now possible for someone to trick downloaders of popular files into send thousands of requests to a webserver of choice, taking it down as a result. Effectively turning BitTorrent into a very effective DDoS tool.

BitTorrent have lived over the years because of their reliability and effectiveness. Unlike a server centric model, where the dependency is on a one server (or distributed servers), its distributed and directly available through individual nodes that auto-discover each other, resulting in faster and more reliable data transfers. This is the reason why, everyday, millions of people (Swarm) use bittorrents to download Terabytes of data.


Hackers have now used the popular DHT technology to abuse BitTorrent downloaders to DDoS a webserver of choice. DHT, under normal operation, discovers peers who are downloading the same files, without communicating with a central BitTorrent tracker. If there are enough peers downloading the same file, this could easily take down medium to large websites. The worrying part is that the downloaders who are participating in the DDoS will not be aware of what’s going on.

“The core problem are the random NodeIDs. The address hashing and verification scheme works for scenarios like the old Internet, but becomes almost useless in the big address space of IPv6,” Astro told TorrentFreak in a comment. As a result, any BitTorrent swarm can be abused to target specific websites and potentially take them down.

These days,  DDoS attacks have been in the news regularly, mostly carried out under the flag of Anonymous “Operation Payback”. Initially anti-piracy targets such as the MPAA and RIAA were taken offline, and last month the focus switched to organizations that acted against Wikileaks, including Mastercard, then Visa and Paypal.

“Not connecting to privileged ports (< 1024) where most critical services reside,” is one ad-hoc solution, but Astro says that since it’s a design error, the protocol has to be redefined eventually.

The idea of using BitTorrent as a DDoS tool is not entirely new. In fact, researchers have previously shown that adding a webserver’s IP address as a BitTorrent tracker could result in a similar DDoS. The downside of this method is, however, that it requires a torrent file to become popular, while the DHT method can simply exploit existing torrents that are already being downloaded by thousands of people.

Over the next few years, it may actually be able to create non-blockable Torrents. Even today, there are ways of Bypassing torrent blocking, throttling. Now, what remains to be seen is that will BitTorrent developers do enough to fix DDoS vulnerability or will it remain open and cause havoc.

You can find the Slides of the presentation here.
Update: Download Video Presentation here

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