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09 January 2009, 15:53

Storm Worm botnet cracked wide open

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A team of researchers from Bonn University and RWTH Aachen University have analysed the notorious Storm Worm botnet, and concluded it certainly isn't as invulnerable as it once seemed. Quite the reverse, for in theory it can be rapidly eliminated using software developed and at least partially disclosed by Georg Wicherski, Tillmann Werner, Felix Leder and Mark Schlösser. However it seems in practice the elimination process would fall foul of the law.

Over the last two years, Storm Worm has demonstrated how easily organised internet criminals have been able to spread this infection. During that period, the Storm Worm botnet has accumulated more than a million infected computers, known as drones or zombies, obeying the commands of a control server and using peer-to-peer techniques to locate new servers. Even following a big clean-up with Microsoft's Malicious Software Removal Tool, around 100,000 drones probably still remain. That means the Storm Worm botnet is responsible for a considerable share of the Spam tsunami and for many distributed denial-of-service attacks. It's astonishing that no one has succeeded in dismantling the network, but these researchers say it isn't due to technical finesse on the part of the Storm Worm's developers.

Existing knowledge of the techniques used by the Storm Worm has mainly been obtained by observing the behaviour of infected systems, but the researchers took a different approach to disarm it. They reverse translated large parts of the machine code of the drone client program and analysed it, taking a particularly close look at the functions for communications between drones and with the server.

Using this background knowledge, they were able to develop their own client, which links itself into the peer-to-peer structure of a Storm Worm network in such a way that queries from other drones, looking for new command servers, can be reliably routed to it. That enables it to divert drones to a new server. The second step was to analyse the protocol for passing commands. The researchers were astonished to find that the server doesn't have to authenticate itself to clients, so using their knowledge they were able to direct drones to a simple server. The latter could then issue commands to the test Storm worm drones in the laboratory so that, for example, they downloaded a specific program from a server, perhaps a special cleaning program, and ran it. The students then went on to write such a program.

This gave them all the basic components they needed to eliminate the Storm Worm network completely. They report that, using a yet to be written extension for a distributed disinfection, even a drone network of more than 100,000 drones can be dismantled, without any danger of a central cleaning server collapsing under the load, or suffering DDoS attacks from botnet operators.

The team has not yet taken the final step of putting the whole thing into action with a genuine Storm Worm botnet in the wild. From a legal point of view, that could involve many problems. Any unauthorised access to third-party computers could be regarded as tampering with data, which is punishable under paragraph § 303a of the German Penal Code. That paragraph threatens up to two years' imprisonment for unlawfully deleting, suppressing, making unusable or changing third-party data. Although this legal process would only come into effect if there was a criminal complaint from an injured party, or if there was special public interest in the prosecution of the crime.

Besides risks of coming up against the criminal law, there is also a danger of civil claims for damages by the owners of infected PCs, because the operation might cause collateral damage. There are almost certain to be configurations in which the cleaning goes wrong, perhaps disabling computers so they won't run any more. Botnet operators could also be expected to strike back, causing further damage.

On the other hand, any botnet of drone computers used for malicious purposes represents a threat to the public at large. Botnets are the main tools used by criminals to collect many millions annually by fraud and extortion. Without them, the internet would be much safer and much more enjoyable. It's surprising that there is no discussion going on regarding the legal preconditions that would have to be created in order to get rid of the threat. In the light of this research the responsible authorities certainly cannot claim that it's technically impossible.


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