Researcher To Release Free 'Slow HTTP Attack' Tool

Slow HTTP attacks can be a lethal form of denial of service to Web servers: they are easy to perform and require minimal computing resources, and they are tough to detect until it's too late. So a researcher is releasing a new open-source tool he wrote that checks a server's vulnerability to such an attack.

The new "slowhttptest" tool, written by Sergey Shekyan, senior software engineer at Qualys, says his tool was inspired by similar open-source tools, Slowloris, and OWASP's Slow HTTP Post tools, and includes some of their features as well as new configurable parameters and other features.

The Slowloris HTTP DDoS tool keeps connections open by sending partial HTTP requests and sends headers at regular intervals to prevent the sockets from closing. The slow HTTP POST 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 at a slow speed to gridlock the connection and use server resources.

Shekyan says his tool lets organizations see their server's vulnerabilities to these types of attacks, so they can better configure them to resist HTTP-layer DDoS attacks. The tool opens customized, slow connections to the server so you can see where it's prone to such attacks. "There is no patch for these slow attacks -- no universal recommendations. It depends on your particular system," he says.

The Slow HTTP DDoS works because of the way the HTTP protocol works: the server must have received a completed HTTP request before it's processed. "If an HTTP request is not complete, or if the transfer rate is very low, the server keeps its resources busy waiting for the rest of the data," Shekyan says.

Shekyan says slowhttptest could be expanded to test for the so-called "ApacheKiller" hack. "They are related in terms that both attacks are able to consume server resources with minimal traffic footprint. Slow HTTP attacks are not targeting a specific platform like Apache, but are universal and work against pretty much all known HTTP servers," he says.

The slowhttpest is available here for download.

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