Strategic Security Survey: Global Threat, Local Pain
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"Our continued research has revealed that as well as being controlled via a command and control infrastructure, the threat also has the ability to update itself via a peer-to-peer component," said Liam O Murchu, writing on Symantec's Security Response Symantec's blog.
The capability works via a remote procedure call (RPC) server and client, which are installed by the malware. "Infected machines contact each other and check which machine has the latest version of the threat installed," he said. "Whichever machine has the latest version transfers it to the other machine and in this way the worm is able to update itself without contacting a central command and control server."
As a result, attackers may still be able to update and control the worm via P2P channels. "The creators of Stuxnet were aware that they might lose control of their command and control servers so they built in a P2P update function to prepare for that eventuality," said Murchu.
Researchers keep finding that there's more than meets the eye to Stuxnet. For example, the malware -- which appears to have been created to exploit SCADA systems designed by Siemens -- also targets a printer spooler service impersonation vulnerability in Microsoft Windows, which may have been first detailed publicly in 2009. The flaw allows Stuxnet to overwrite a printer spooler file and propagate. Microsoft patched the vulnerability last week as part of its September 2010 Patch Tuesday.
Another interesting finding made by Symantec is that while the malware appeared to be a never-before-seen, zero-day attack, it now appears that variants date from at least June 2009.