Much has been written about these techniques at length, so I will summarise the main methods we have used historically as penetration testers for on-disk AV bypass.Įncoding generally involves modifying the signature of the binary such that the AV won’t detect it. I was amused it succeeded so easily, so I wanted to compare my own code with common methods/tools used to bypass AV. Relatively simple C# code was written to create a basic reverse shell, back to a netcat connection, which then bypassed a popular corporate-grade AV. Generating FUD code can be achieved by writing custom code that AV has no knowledge of. In this instance, we are interested in generating code that will bypass the AV installed on the host we are trying to compromise. This is to check if a customer is vulnerable and to better mimic the threats that are being faced. If you google FUD you may get some ‘interesting’ definitions of the Celtic variety from the urban dictionary! For the purposes of this article and from a security perspective, FUD is the acronym to describe a piece of code that is Fully UnDetectable by Anti-Virus (AV) software.įrom a penetration testing perspective we want to replicate what the bad guys are doing in a safe manner. Therefore allowing the payload to bypass all controls, execute and make the attachment enticing enough for the user to open it. The goal of the attacker is to create a payload in the attachment that is Fully UnDetectable (FUD) by Anti-Virus (AV) software. In the case of this malware, it's being sent as attachments. This is something we've seen in the recent NHS WannaCry and Petya/NotPetya ransomware breakouts (as badly orchestrated as they may both have been). It can then do anything from sit in the background as a zombie waiting for the next instruction, or something more sinister, such as lock your computer and demand payment. Using phishing or social engineering based attacks, criminals attempt to lure an unsuspecting victim into launching a malicious piece of code.
Malware continues to be one of the main attack vectors used by criminals to compromise user and corporate data.
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