New Denial Of Service Attack Cripples Servers Slowly

A researcher Thursday published proof-of-concept code that takes a different spin on the slow HTTP denial-of-service (DoS) attack simply by dragging out the process of reading the server's response--and ultimately overwhelming it.

Sergey Shekyan, senior software engineer with Qualys, also has added this new so-called Slow Read attack to his open-source slowhttptest tool.

Slow Read basically sends a legitimate HTTP request and then very slowly reads the response, thus keeping as many open connections as possible and eventually causing a DoS.

Shekyan's Slowhttptest attack tool initially was inspired by related open-source tools Slowloris and OWASP's Slow HTTP Post. Slowloris keeps connections open by sending partial HTTP requests and sends headers at regular intervals to prevent the sockets from closing, while the Slow HTTP POST distributed DoS (DDoS) tool simulates an attack using POST headers with a legitimate "content-length" field that lets the Web server know how much data is arriving. Once the headers are sent, the POST message body is transmitted slowly, thus gridlocking the connection and server resources.

Slow HTTP attacks are gaining in popularity among the bad guys as a way to quietly wage a DoS attack because these exploits are relatively easy to perform, require minimal computing resources, and often are tough to detect until it's too late.

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