Microsoft Security Response Center
6 Jun 2012
Today, as a part of our continuing phased mitigation strategy recently discussed, we have initiated the additional hardening of Windows Update. We’ve also provided more information about the MD5 hash-collision attacks used by the Flame malware in the SRD blog. This information should help answer questions from customers about the nature of these collision attacks. We continue to encourage all customers who are not installing updates automatically to do so immediately.
Security Research & Defense
6 Jun 2012
Flame malware collision attack explained
Since our last MSRC blog post, we’ve received questions on the nature of the cryptographic attack we saw in the complex, targeted malware known as Flame. This blog summarizes what our research revealed and why we made the decision to release Security Advisory 2718704 on Sunday night PDT. In short, by default the attacker’s certificate would not work on Windows Vista or more recent versions of Windows. They had to perform a collision attack to forge a certificate that would be valid for code signing on Windows Vista or more recent versions of Windows. On systems that pre-date Windows Vista, an attack is possible without an MD5 hash collision. This certificate and all certificates from the involved certificate authorities were invalidated in Security Advisory 2718704. We continue to encourage all customers who are not installing updates automatically to do so immediately.