One of the most popular exploit frameworks in the world is Metasploit. Its vast library of pocket exploits, pluggable payload environment, and simplicity of execution makes it the de facto base platform. Metasploit is used by pentesters, security enthusiasts, script kiddies, and even malicious actors. It is so prevalent that its user base even includes APT threat actors, as we will demonstrate later in the blog post.
Despite Metasploit’s over 15 year existence, there are still core techniques that go undetected, allowing malicious actors to evade detection. One of these core techniques is the Shikata Ga Nai (SGN) payload encoding scheme. Modern detection systems have improved dramatically over the last several years and will often catch plain vanilla versions of known malicious methods. In many cases though, if a threat actor knows what they are doing they can slightly modify existing code to bypass detection.
Before we jump into how SGN works we’ll give a little background knowledge surrounding it. When threat actors plan to attack systems, they go through an assessment process of risk and reward. They cycle through questions of stealth and attribution. Some of these questions include: How much effort do I need to put into not getting caught? What happens if I get caught? How long can I reasonably evade detection? Will the discovery of my presence be attributed back to me? One such way APT actors have attempted to elude detection in the first place has been via encoding.