Researchers at Huntress Labs have uncovered what they described as a really clever use of Windows batch scripting by the authors of Trickbot to try and sneak the latest version of their malware past automated detection tools.
The technique takes advantage of the way the Windows command line interpreter, cmd [.] exe, reads and interprets data that is typed on the command line.
What the authors of Trickbot have done is use a batch script to break up their payload into numerous small chunks and then use the command line interpreter to rebuild the original payload, says John Hammond, senior security researcher at Huntress.
"The gist of this technique is substituting each character in a payload with a new mapped value, so the payload can be slowly created with building blocks."
This technique isn't specific to Trickbot. In fact, any other code or malware sample can do this within Windows batch scripting, Hammond says. But this is the first time that Huntress has observed a threat actor using this exact obfuscation technique, he says. "It seems to be a very simple technique, and now that Trickbot has introduced it, it may become more popular."
Though PowerShell and other command line tools are now available for Windows, cmd [.] exe remains the default command line interpreter for the operating system, as it has for decades. The technology makes a good target for attackers because it provides an interactive interface that they can use to execute commands, run malicious programs, delete files, and carry out a variety of other actions.
Typically, the command prompt can be hardened and lo ..
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