Tuesday, February 11, 2014

Careto: Covering unavailable samples

Kaspersky labs released a report that covers in detail a piece of malware known as "Careto" or "The Mask". The report included several MD5 hashes of samples and related files, IP addresses and domain information. Typically with ClamAV,  a hash signature targeting an entire file is formatted as following:

MD5:FileSize:Name

The samples for Careto and therefore their sizes were unavailable to us at the time of this blog post, making it impossible to release hash-based coverage. However, as of ClamAV 0.98, a hash signature can be written with a wildcard for the file size. The format for such a signature is:

MD5:*:Name:73

The 73 on the end will prevent the signature from being loaded by an older ClamAV engine that doesn't support this signature format.

The Mask is a combination of tools that cover 32-bit and 64-bit Windows, Mac OS X and Linux. Kaspersky also identified potential Android and Apple iOS variants. Their analysis indicates it can intercept many different forms of communication from the victim machine, exfiltrate data and provide remote access to the attacker.

This signatures file can be used to detect the sample discussed in the article. Just download it and put it in the same folder where you have your ClamAV signatures. If any alerts are generated from these please let us know by emailing research < at > sourcefire (dot) com.

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