Microsoft has released further details on the MD5 hash collision attacks utilized by the Flame malware to sign its code and make it look like it came from the company.
According to experts, at first glance Flame appeared to have a valid digital signature, but after further analysis, they reached the conclusion that there were many irregularities.
For instance, it had no X.509 extension fields, and the Certificate Revocation List (CRL) Distribution Point (CDP) extension, the “Microsoft Hydra” critical extension, and an Authority Information Access (AIA) extension were missing.
Researchers have explained that the collision attacks were performed by Flame’s masterminds because they were needed to forge certificates that would be valid for code signing on Windows Vista and more recent versions of the operating system.
The rogue certificates would not work on these Windows variants and that’s why the cybercriminals had to come up with the clever way of making them valid for code signing.
To minimize the risks, Microsoft not only made some modifications to the Terminals Server Licensing Certificate infrastructure, but they’ve also released the out-of-band update that most users should have applied by now.
On the other hand, Marc Stevens and Benne de Weger, specialists in the field of rouge certificates, have revealed some interesting findings, naming the MD5 chosen-prefix collision attacks “unknown.”
“We have confirmed that Flame uses a yet unknown md5 chosen-prefix collision attack. We are interested in other possible certs based on this md5 coll attack for further analysis,” they explained.
“We are now analyzing their chosen-prefix collision attack in more detail, (more examples would greatly help) and trying to write up some results and conclusions to make a more detailed statement. The collision attack itself is very interesting from a scientific viewpoint and there are already some practical implications.”
Via: Experts Name Flames MD5 Chosen-Prefix Collision Attack Unknown
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