Wednesday, June 17, 2009

Slowloris HTTP DoS

As you may recall at one point a few weeks back I talked about how denial of service can be used for hacking and not just yet another script kiddy tool. Well I wasn’t speaking totally hypothetically. A month ago, or so, I was pondering Jack Louis (RIP) and Robert E Lee’s Sockstress, and I got the feeling that other unrelated low bandwidth attacks were possible. Then I randomly started thinking about the way Apache works and figured out that it may be possible to create something similar to a SYN flood, but in HTTP.

Slowloris was born. It basically uses a concept of keeping an HTTP session alive indefinitely (or as long as possible) and repeating that process a few hundred times. So in my testing, against an unprotected and lone Apache server, you can expect to be able to take it offline in a few thousand packets or less on average, and then you can let the server come back again as soon as you kill the process. It also has some stealth features, including a method of bypassing HTTPReady protection. Why is this noteworthy?



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