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Storm Worm Botnet:
Lobotomizing Anti-Virus Programs

New technique leaves AV running but brain-dead; expert says we haven't come close to witnessing Storm's true power.

NEW YORK—The ever-mutating, ever-stealthy Storm worm botnet is adding yet another trick to its vast repertoire: Instead of killing anti-virus products on target systems, it's now doing a hot fix with a memory patch to render resident AV products brain-dead.

The finding was made by Sophos and was mentioned by Joshua Corman, a principal security strategist for IBM Internet Security Systems, Oct. 23 in his presentation here at Interop New York 2007 on the challenge of evolving cyber threats.

According to an Oct. 22 posting by Sophos analyst Richard Cohen, the Storm botnet—Sophos calls it Dorf, and it's also known as Ecard malware—is dropping files that call a routine that gets Windows to tell it every time a new process is started. The malware checks the process filename against an internal list and kills the ones that match—sometimes. But Storm has taken a new twist: It now would rather leave processes running and just patch entry points of loading processes that might pose a threat to its. Then, when processes such as anti-virus programs run, they simply return a value of 0.

"Programs, including not just AV exes, dlls and sys files, but also software such as the P2P applications BearShare and eDonkey, will appear to run successfully, even though they didn't actually do anything, which is far less suspicious than a process that gets terminated suddenly from the outside," Cohen wrote in the posting.

The strategy means that users won't be alarmed by their AV software not running. Even more ominously, the technique is designed to fool NAC (network access control) systems, which bar insecure clients from registering on a network by checking to see whether a client is running AV and whether it's patched.

"It's running but brain dead. It's worse than shutting it off," as it opens the door for Storm bots to waltz past even networks considered to be hardened with NAC, Corman said during his Interop presentation.

It's the latest evidence of why Storm is "the scariest and most substantial threat" security researchers have ever seen, he said. Storm is patient, it's resilient, it's adaptive in that it can defeat AV in multiple ways (programmatically, it changes its signature every 30 minutes), it's invisible because it comes with a rootkit built in and hides at the kernel level, and it's clever enough to change every few weeks.

It has its own mythology: Comprised of up to 50 million zombie PCs, it has as much power as a supercomputer, the stories go, with the brute strength to crack Department of Defense encryption schemes.

In reality, security researchers in the know peg the size of the peer-to-peer botnet at 6 million to 15 million PCs, and not on par with a supercomputer. And it can't break encryption keys. Still, it has security researchers terrified, Corman said.

"[Storm is] the scariest and most substantial threat we've ever seen," he said. "There's a lot of exaggerations of how many systems are infected … [and how its power is like that of a supercomputer]. That's fiction. It's still a lot of power, though. … Some of my best and highest-profile clients are very concerned about Storm right now."

Storm's mystique comes in part from one of the most challenging aspects to dealing with the botnet: Its rabid self-defense mechanisms.

"If you try to attach a debugger, or query sites it's reporting into, it knows and punishes you instantaneously," he said. "[Over at] SecureWorks, a chunk of it DDoS-ed [directed a distributed denial of service attack] a researcher off the network. Every time I hear of an investigator trying to investigate, they're automatically punished. It knows it's being investigated, and it punishes them. It fights back."

Those researchers who have devised ways to accurately research the scope, techniques and technologies of the botnet are hushed up by their superiors who are well aware of the retribution that botnet herders have already wrought on those who tried to defeat them, Corman said.

Hence the hush-hush nature of research around Storm. He can tell us that it's now accurately pegged at 6 million, but he can't tell us who came up with the figure, or how, Corman said. Besides retribution, Storm's ability to morph means that those who know how to watch it are jealously guarding their techniques. "None of the researchers wanted me to say anything about it," Corman said. "They're afraid of retaliation. They fear that if we disclose their unique means of finding information on Storm," the botnet herder will change tactics yet again and the window into Storm will slam shut.

What really has his clients worried, though, is what Storm hasn't yet done, Corman said, with the exception of small hits such as that against SecureWorks or other researchers—ransom sites with DDoS.

There's precedent for such a scenario, and the results haven't been cheering. When it comes to the war of good guys (security researchers) vs. bad guys (botnet herders), botnets have won, hands down.

Corman referenced the case of Blue Security, an Israeli-based startup whose aggressive antispam measures in May 2006 drew a counterattack from spammers that was so vicious, it forced the company out of business."

"Somebody wrote a [botnet], and Blue Security did a really good job of fighting," Corman said. "So [the attackers] did a DDoS and took it off the Net for awhile. Blue Security went to the best anti-DDoS technology on earth. The next onslaught came and [Blue Security's defenses] worked. So the botnet herder stole two other people's botnets. With three botnets, [the attack] worked, to the point where the ISP said, 'I'm not going to let you take down my entire ISP to protect you, you're on own.' And Blue Security is now out of business."

A particularly disturbing point to keep in mind, Corman said: Botnets in May 2006 were very, very small, compared to Storm.

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