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June 18 2009

finkregh

Slowloris HTTP DoS

Slowloris holds connections open by sending partial HTTP requests. It continues to send subsequent headers at regular intervals to keep the sockets from closing. In this way webservers can be quickly tied up. In particular, servers that have threading will tend to be vulnerable, by virtue of the fact that they attempt to limit the amount of threading they'll allow. Slowloris must wait for all the sockets to become available before it's successful at consuming them, so if it's a high traffic website, it may take a while for the site to free up it's sockets. So while you may be unable to see the website from your vantage point, others may still be able to see it until all sockets are freed by them and consumed by Slowloris. This is because other users of the system must finish their requests before the sockets become available for Slowloris to consume. If others re-initiate their connections in that brief time-period they'll still be able to see the site.
Tags: security http apache networking cracking dos
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