Original URL: http://www.theregister.co.uk/2010/08/05/conficker_analysis/

Conficker's 6m strong botnet confounds security probes

Cross-industry group baffled by super crypto shield of infamous botnet

By John Leyden

Posted in Security, 5th August 2010 13:28 GMT

Analysis The unknown crooks behind the infamous Conficker worm may be quietly selling off parts of the huge botnet established by the malware, but virus fighters have no way of knowing because the cryptographic defences of its command and control network have proved uncrackable.

Conficker (aka Downadup) first appeared in November 2008, originally using a recently patched vulnerability in Windows Server Service to infect insecure systems. Later its ability to spread through network shares and to hop over onto PCs from infected USB sticks became its primary spreading mechanism.

Early victims included the Houses of Parliament and the Ministry of Defence in the UK. Conficker's aggressive scanning routines swamped legitimate traffic on compromised networks, creating all sorts of problems in the process.

Interest in the worm peaked around 1 April 2009 when its algorithm changed so that it "phoned home" to a far larger number of pre-programmed domains, sparking fears that new instructions would be applied activating a huge network of zombie computers to send spam or launch denial of service attacks.

In the event, 1 April came and went without anything of note happening, leading some to wrongly label the malware as a damp squib. Although the Conficker botnet remains largely dormant an estimated six million Windows PCs remain infected with the threat.

Wide open backdoor

These Windows boxes remain wide open to further attack not least because Conficker is programmed to turn off Windows update and anti-virus software on compromised machines, according to Rodney Joffe, a director of the Conficker Working Group. The still-active working group is made up of a team of security, domain name, law enforcement and government representatives brought together to fight the Conficker threat.

Early tasks of the group included blocking the registrations of domains that machines infected with early variants of Conficker were programmed to contact for further instructions. Subcommittees of the group focused on issues such as reverse engineering the malware's code, dealing with the sinkhole domains that infected bots were programmed to contact, and community outreach work.

Rodney Joffe, a senior technologist at net infrastructure firm Neustar, dismisses the theory that Conficker was a failed experiment or "research project" by cybercrooks, perhaps one that was too successful to be useful. In particular he's dismissive of the idea that the botnet remains dormant because activating it would provoke unwelcome law enforcement attention.

"Conficker was not a bust. It's still causing enormous problems and damage as a byproduct of infection," Joffe told El Reg.

Around six million systems remain infected with either the A or B variants of Conficker. The C variant, which used a P2P method of distribution, affects a lower number of around 120,000, as illustrated by an infection tracker maintained by the Conficker Working Group here.

Windows PCs infected with the C variant of Conficker were programmed to download Spyware Protect 2009 (a scareware package) and the Waledac botnet client, a strain of malware associated with spamming.

"These are different gangs and suggest the malware authors behind Conficker have a trading relationship with bad guys," Joffe explained.

International rescue

The Conficker Working Group constantly monitors the IP addresses of infected machines as they check into sink holes. Many enterprises associated with infections drop off the radar only to return days or weeks later, probably as the result of the application of infected backups that have not been purged of malware.

Utilities such as Microsoft's Malicious Software Removal Tool, effective in cleaning up other infections, have proved ineffective against Conficker because software security updates get disabled on compromised machines.

"Conficker has created a stable pool of around six million infected machines," Joffe warned. "These machines are running without updates or anti-virus defences which creates a wide open backdoor."

Joffe warns that criminal hackers could register "phone home" domains associated with Conficker to harvest a list of infected IP addresses. This list could then be used as a targeting mechanism for attacks, safe in the knowledge that machines as the receiving end of exploits would be defenceless.

Attacks could be narrowed down to target systems known to be insecure rather than scanning for vulnerabilities, a noisy activity likely to set off warnings.

Blocking the registration of domains would thwart such an approach, but a "number of registries" are no longer collaborating with the Conficker Working Group, Joffe warned.

Mystery super-villains

The miscreants behind the worm remain unknown and the purpose of the malware unclear. Joffe would only say that there was an active law enforcement investigation without giving any clues as to how it was proceeding.

Joffe said the cybercrooks behind Conficker were highly sophisticated and competent coders who used "bleeding edge" cryptographic techniques and responded to the efforts of the anti-virus community with progressively more sophisticated variants of their malware.

The latest variants of Conficker use MD6, a candidate for a federal encryption standard due to be formalised only in 2012, and the crooks were smart enough to apply patches days after earlier shortcomings of the scheme were discovered by cryptoanalysts.

"We can't take over the botnet and we don't know what it's doing - it's uncrackable," Joffe explained. "The cybercrooks behind the Conficker might hive off components of the botnet to other bad guys and we wouldn't have a clue. The loss of hundreds of machines would be indistinguishable from background noise."

Although perhaps not as active as during its peak last year, the core part of the committee remains active and meets every fortnight. Activities including outreach to hospitals (many of which were hit by serious Conficker infections only this year) remain an important part of its work. "We'll continue as long as the Conficker threat remains," Joffe concluded, adding that 18 months after the first outbreak new infections are still appearing.

Butterfly collector

The Conficker Working Group, the first cross-industry organisation of its kind to fight a malware threat, formed the blueprint for the later Mariposa Working Group. The takedown of the main 12 million strong information-stealing Mariposa botnet and the arrests of three suspects in Spain prompted a decision to disband this group, whose work had reached completion.

An active law investigation into the trio in Spain, alleged clients of the Butterfly botnet client allegedly developed by Slovenian coders, remains ongoing. A suspect, later identified as Dejan Janžekovic by ex-Washington Post staffer Brian Krebs, has become the focus of the police investigation in Slovenia.

Joffe declined to answer questions about the Mariposa investigation beyond saying that two or three other groups who used the Butterfly botnet kit are of potential interest to international police investigating the case. "The Spanish group were very successful in getting the Butterfly botnet kit, but its use was fairly widespread." ®