Original URL: http://www.theregister.co.uk/2009/03/26/conficker_activation_analysis/

Final countdown to Conficker 'activation' begins

T-minus six

By John Leyden

Posted in Security, 26th March 2009 13:46 GMT

Security watchers are counting down to a change in how the infamous Conficker (Downadup) worm updates malicious code, due to kick in on Wednesday 1 April.

Starting on 1 April, Windows PCs infected by the latest variant of the Conficker worm (Conficker-C) will start attempting to contact a sample of 50,000 pre-programmed potential call-home web servers from which they might receive updates, a massive increase on the 250 potential web server locales used by earlier variants of the code.

"Conficker-C isn't going to contact all 50,000 domains per day," explained Niall Fitzgibbon, a malware analyst at Sophos. "It's only going to contact a randomly-chosen 500 of them which gives each infected machine a very small chance of success if the authors register only one domain. However, the P2P system of Conficker can be used to push digitally signed updates out to other infected machines that don't manage to contact the domain."

Known unknown

Whether anything will actually be offered for download, much less what the payload might be, is unclear. No particular function or payload currently within the malicious code is due to activate on 1 April. It's also possible that a payload will only be offered up for download days or week after the new call-home routine comes into effect.

If updates are successfully made, infected machines are programmed to suspend call-home activity for 72 hours, as an analysis by Sophos explains.

Lessons from the call back routines of previous variants of the worm provide few clues as to what might happen. Sophos said it never observed the previous Conficker-B variant ever downloading malicious payloads, other than updates to Conficker-B++ and Conficker-C. As a result, there isn't much history to draw upon for any speculation as to the eventual goal of the Conficker botnet.

Anti-virus firms are keeping a close eye on what Conficker might do early next month while downplaying concerns that Downadup will either "erupt" or "explode" on 1 April, deluging us with spam or swamping websites with junk traffic in the process.

"Let's not forget that history has shown us that focusing on a specific date for an impending malware attack has sometimes lead to nothing more than a damp squib," notes Graham Cluley, senior technology consultant, at Sophos.

Although nothing might happen it's never a bad time for sys admins to check for infection by Conficker on their network. Such infections have already caused widespread problems.

Symantec said that the worm, which had initially focused solely on spreading "has since developed into a robust botnet, complete with sophisticated code signing to protect update mechanisms, as well as a resilient peer-to-peer protocol". An analysis of the worm, complete with a graphic illustrating the evolution of the worm's propagation, control and defensive features, can be found here.

Windows PCs infected with Conficker (Downadup) are programmed to dial home for updates through a list of pseudo-random domains. Microsoft is heading a group, dubbed the anti-cabal alliance, to block unregistered domains on this list. The more complex call-home routine deployed by Conficker-C comes in apparent response to this move.

Rik Ferguson, a security researcher at Trend Micro, added that blocking call-back domains associated with the latest variant of the worm will be "almost impossible" not only because of the daily volume, but also because there is a possibility that legitimate domains might be hit as a result. Even earlier versions of the worm, calling far fewer domains every day, used algorithms that threw up addresses that coincided with legitimate domains.

Ferguson has put together a couple of useful graphics illustrating how Conficker works, in an analysis here.

The most detailed and thorough technical analysis of the worm's behaviour can be found in a paper by SRI International here.

Birth of a superworm

Variants of the Conficker worm, which first appeared back in November, spread using a variety of tricks. All strains of the superworm exploit a vulnerability in the Microsoft Windows server service (MS08-067) patched by Redmond in October.

Once it infects one machine on a network, the worm spreads across network shares. Infection can also spread via contaminated USB sticks. This combined approach, in particular the worm's attempts to hammer across corporate LANs, have made Conficker the biggest malware problem for years, since the default activation of the Windows firewall put the brakes on previous network worms such as Nimda and Sasser.

Compromised Windows PCs, however the infection happens, become drones in a botnet, which is yet to be activated. It's unclear who created or now controls this huge resource.

Estimates of the number of machines infected by Conficker vary, from barely over a million to 12 or even 15 million. More reliable estimated suggest that between 3-4 million compromised systems at any one time might be closer to the mark.

SRI reckons that Conficker-A has infected 4.7m Windows PC over its lifetime, while Conficker-B has hit 6.7m IP addresses. These figures, as with other estimates, come from an analysis of call-backs made to pre-programmed update sites. Infected hosts get identified and cleaned up all the time, as new machines are created. Factoring this factor into account the botnet controlled by Conficker-A and Conficker-B respectively is reckoned to be around 1m and 3m hosts, respectively, about a third of the raw estimate.

Estimates of how many machines are infected by the Conficker-C variant are even harder to come by.

But however you slice and dice the figure its clear that the zombie network created by Conficker dwarfs the undead army created by the infamous Storm worm, which reached a comparatively lowly 1 million at its peak in September 2007. Activation of this resource may not come next week or even next month but the zombie army established by the malware nonetheless hangs over internet security like a latter-day Sword of Damocles.

Some security watchers are sure it will get used eventually, if not on 1 April. Sam Masiello, a security analyst at MX Logic, said: "Why go through all of this effort to create such a huge botnet then not utilize it for something?"

"In a financially motivated economy it doesn't make sense to not rent it out or sell it off," he adds. ®

Bootnote

The humour potential of the April Fool's Day timing of Conficker's change of gears hasn't been lost on security researcher, some of who has mined a vein of horror and computer security cross-over humour.

Noted security researcher Chris Boyd of FaceTime Security notes the April Fool's Day significance of Conficker's "activation" date with a series of wry Conficker prediction such as "Sadako crawls out of your TFT monitor and EATS YOUR FACE" and "Satan himself emerges from your mouse wheel, whines about convergent technology then EATS YOUR FACE", that can be found here.

More seriously Symantec notes that searches for the term Conficker C have been contaminated to point at sites offering scareware packages, using black-hat search engine optimisation techniques. Be careful out there.