Ransomware: Locky, TeslaCrypt and other malware families use new tool to evade detection
Recently, Palo Alto Networks identified slight changes in Locky detonations through the AutoFocus threat intelligence service, correlating global data to discover a new tool being used to pack multiple ransomware families. Adversaries are constantly seeking new techniques to bypass security controls, and based on data from AutoFocus, this represents a widespread update to their tradecraft.
In their analysis, multiple malware samples stood out due to what seemed like obfuscated API calls coming from a dictionary of embedded terms to resolve system functions and hide their true capabilities from commonly used static analysis tools.
Tampering with the API calls takes away the ability to classify based on key names, thus increasing the likelihood that the malware will go undetected. This, however, is where it gets interesting, as it appears this was just the first in a series of misdirections designed to throw off analysts.
When looking at the new samples, the import tables for libraries to load on execution would differ significantly and not actually be used at all during execution. This prevented any sort of meaningful detection by import hashing. Additionally, looking at the executable version information showed varying information per sample but a clear pattern that can be used for future identification.
Palo Alto Networks has identified this technique being picked up recently by the Locky ransomware, but they have also identified samples of TeslaCrypt and Andromeda malware families, dating back to March 14, 2016 that exhibit the technique.
