How BitTorrent could let lone DDoS attackers bring down big sites

Some of the most widely used BitTorrent applications, including uTorrent, Mainline, and Vuze are also the most vulnerable to a newly discovered form of denial of service attack that makes it easy for a single person to bring down large sites.

The distributed reflective DoS (DRDoS) attacks exploit weaknesses found in the open BitTorrent protocol, which millions of people rely on to exchange files over the Internet. But it turns out that features found uTorrent, Mainline, and Vuze make them especially suitable for the technique. DRDoS allows a single BitTorrent user with only modest amounts of bandwidth to send malformed requests to other BitTorrent users.

The BitTorrent applications receiving the request, in turn, flood a third-party target with data that's 50 to 120 times bigger than the original request. Key to making the attack possible is BitTorrent's use of the user datagram protocol, which provides no mechanism to prevent the falsifying of IP addresses. By replacing the attacker's IP address in the malicious request with the spoofed address of the target, the attacker causes the data flood to hit victim's computer.