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We recently became aware of a complex piece of targeted malware known as “Flame” and immediately began examining the issue. As many reports assert, Flame has been used in highly sophisticated and targeted attacks and, as a result, the vast majority of customers are not at risk. Additionally, most antivirus products will detect and remove this malware. That said, our investigation has discovered some techniques used by this malware that could also be leveraged by less sophisticated attackers to launch more widespread attacks. Therefore, to help protect both targeted customers and those that may be at risk in the future, we are sharing our discoveries and taking steps to mitigate the risk to customers.
We have discovered through our analysis that some components of the malware have been signed by certificates that allow software to appear as if it was produced by Microsoft. We identified that an older cryptography algorithm could be exploited and then be used to sign code as if it originated from Microsoft. Specifically, our Terminal Server Licensing Service, which allowed customers to authorize Remote Desktop services in their enterprise, used that older algorithm and provided certificates with the ability to sign code, thus permitting code to be signed as if it came from Microsoft.
We are taking several steps to remove this risk:
• First, today we released a Security Advisory outlining steps our customers can take to block software signed by these unauthorized certificates.
• Second, we released an update that automatically takes this step for our customers.
• Third, the Terminal Server Licensing Service no longer issues certificates that allow code to be signed.
These actions will help ensure that any malware components that might have been produced by attackers using this method no longer have the ability to appear as if they were produced by Microsoft.
We continue to investigate this issue and will take any appropriate actions to help protect customers. For more information, please refer back to this site and check with your anti-malware vendor for detection support.
Additionally, we offer more technical details about the steps we are taking on the SRD Blog.
If you have not done so already, we highly recommend registering for our comprehensive security alerts. Sign up here: Microsoft Technical Security Notifications.
Thanks, Mike Reavey Senior Director, MSRC Microsoft Trustworthy Computing