Fox-IT Completes the Picture On Factored RSA-512 Keys

During recent weeks we have observed several interesting publications which have a direct relation to an investigation we worked on recently. On one hand there was a Certificate Authority being revoked by Mozilla, Microsoft and Google (Chrome), on the other hand there was the disclosure of a malware attack by Mikko Hypponen (FSecure) using a government issued certificate signed by the same Certificate Authority. That case however is not self-contained and a whole range of malicious software had been signed with valid certificates. The malicious software involved was used in targeted attacks focused on governments, political organizations and the defense industry. The big question is of course, what happened, and how did the attackers obtain access to these certificates? We will explain here in detail how the attackers have used known techniques to bypass the Microsoft Windows code signing security model.

Recently Mikko Hypponen wrote a blog on the F-Secure weblog detailing the discovery of a certificate used to sign in the wild malware. Specifically this malware was embedded in a PDF exploit and shipped in August 2011. Initially Mikko also believed the certificate was stolen, as that is very common in these days, with a large amount of malware families having support, or optional support, for stealing certificates from the infected system. Apparently someone Mikko spoke to mentioned something along the lines that it had been stolen a long time ago. During the symposium Mikko mentioned the certificate again, but now he mentioned that according to the people involved with investigating the case in Malaysia it likely wasn’t stolen.