Dark Reading

A researcher has unleashed a free denial-of-service (DoS) hacking tool for flooding TCP sessions.

Called LetDown, the penetration testing tool is part of a larger package of tools called Complemento that was created by Italian researcher Acri Emanuele. "Complemento is a collection of tools that I originally grokked up for my personal toolchain for solving some problems or just for fun," Emanuele wrote in his post announcing the availability of the tools. He also admits having concerns about releasing LetDown to the public.

"I had some doubts, because with this tool [it] is possible to crash a server configured in the wrong way using very slow connections, without the need of botnets. A great fun for script kiddies," Emanuele told Dark Reading.

"Basically, LetDown is a TCP flooder that completes the three-way handshake and sends a requests to the server without closing the connection," he said. "LetDown is aimed specifically at pen testers and server owners that want to test the resiliency of their networks against DoS attacks in order to properly configure the rules on resource management on their systems."

The other Complemento tools include a domain scanner called Reverse Raider that brute-force scans target subdomains or performs reverse-resolution for IP address ranges, and Httsquash, an HTTP server scanner, banner grabber, and data retriever. Complemento is available here for download.

A TCP "flood" attack can take down a Website, for instance. And as with any hacking tool, the danger is that LetDown could fall into the wrong hands. "This tool will have some negative impact for its victims," says Robert E. Lee, chief security officer of Outpost24.

LetDown may be useful for testing for DoS weaknesses, says Jack Lewis, a senior researcher with Outpost24, who, along with Lee, recently discovered a TCP DoS vulnerability that executes a lethal DoS attack against broadband Internet connections. "Some people want to test a network against DoS attacks. I don't think many do, but it may be useful to someone," he says. "It would be a lot more helpful, though, if there were workarounds to these problems," which there are in this case, he notes.

While security experts say it's rare for DoS hacking tools to be released these days, other similar tools have been around for some time. "'Unicornscan' can do it better," for example, Lewis says.

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