It was only a matter of time before we felt Flame's aftershock. Yesterday morning it finally happened. Microsoft published an emergency Security Advisory 2718704 and an associated patch that revokes trust from three intermediate CA certificates:
- Microsoft Enforced Licensing Intermediate PCA (2 certificates)
- Microsoft Enforced Licensing Registration Authority CA (SHA1)
As predicted in our Threat Predictions 2012 paper, the use of rogue certificates for targeted attacks is still "trendy". According to Microsoft there are "active attacks using unauthorized digital certificates derived from a Microsoft Certificate Authority". Later on, Microsoft stated in a post that some components of the Flame malware "were signed with a certificate that chained up to the Microsoft Enforced Licensing Intermediate PCA certificate authority, and ultimately, to the Microsoft Root Authority."
So how did the "bad" guys manage to "steal" those intermediate certificates?
Apparently, certificates that are generated by Microsoft's "Terminal Services licensing certification authority" that are only intended to be used for license server verification, can also be used for signing code – as if this code was delivered by Microsoft. It seems that this flaw was used for signing Flame's components.
As we at the SpiderLabs posted before, we keep monitoring and researching Flame's case to provide the best protection to our customers. Today we have released a Security Update for all versions of Trustwave Secure Web Gateway that revokes the trust in those intermediate CAs. That means that even if the attackers sign or signed more binaries with these rogue certificates, SWG will block them all.
We'll continue to monitor the situation and post more updates as necessary.