IPS Evasion Equation

If you think running multiple vendors' intrusion prevention system (IPS) tools on your network buys you extra protection, think again.

A French researcher will show attendees at the Black Hat conference in Las Vegas next week how he was able to easily slip a well-known worm past three different vendors' IPSes sitting in-line on a network.

Renaud Bidou created a tool that infects a Windows server with the Blaster worm in disguise. He'll also discuss at Black Hat another tool he built that detects whether a network is running an IPS. Bidou, a security consultant with Radware, conducted the research independently to see what it takes to get past an IPS.

But unlike many other researchers at Black Hat, Bidou won't demonstrate his exploit "live" -- he didn't want to single out any particular IPS vendors -- but is providing his proof-of-concept code to the public domain. "The purpose of my presentation is not to say IPS is garbage or it will fade away," he says. "Radware sells IPSes, and I know these devices as well as that of our competitors. These devices have their weaknesses" and enterprises purchasing these devices need to understand what they can and cannot do, he says.

Bidou's "rpc-evade-poc tool" includes the Blaster worm, though slightly repackaged by Renaud to evade the IPSes' signatures and disarmed so it won't propagate like it normally would. Blaster goes after the heap overflow vulnerability (which is patchable today) in a Windows server at the remote procedure call (RPC) layer. "Thanks to the heap overflow, the exploit makes it possible to have a program, running with administrator rights, launch any command or other program with administrator privileges," Bidou explains. Then the attacker could see, copy, or transfer any files on the machine, for instance.

"The purpose of this is not to release a new vulnerability, but to show that you can bypass IPS even with very old and known exploits. I was able to bypass all of the IPSes with a worm that's more than three years old," he says.

But this is no script-kiddie job. An attacker would need to be knowledgeable about the mode of attack as well as the protocols he or she was using, such as RPC or HTTP, Bidou says.

His homegrown fingerprinting tool, meanwhile, detects whether an organization has an IPS running or not, presumably as a precursor to an attack. "I show how easy it is to detect when an IPS is protecting a system -- even if they are supposed to be stealth." The tool, called "ips-http-detect," analyzes anomalies in the communication flow that are typical of an IPS, he says.

— Kelly Jackson Higgins, Senior Editor, Dark Reading