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Below I outline all of the roadblocks I hit and how to work around them.
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There are a number of constraints when working with BOFs that are not limited to their non-job nature. If you want to execute a long running task in beacon, take advantage of execute-assembly and its nature of treating those items as long running jobs. The creator outlines this well here:, but it is important to note.īOFs are most appropriate for one-off commands that will return results quickly. It is not a true plugin format, and it is not treated as such. BOFs are not structured in a way that allows for long running tasks. You also do not have the Indicators of Compromise (IoCs) associated with execute-assembly where you would start your spawn-to process and inject code into it.Īt this point, you may be thinking perfect, let’s recode all of our C# tools into BOFs.
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When a technique is coded using a BOF, you gain the benefit of running code inside of beacon itself and without starting a child process. This is well known and outlined by the creator here. Typically, Cobalt Strike will always perform cross-process injection or start cmd.exe / powershell.exe to accomplish its more useful goals. Why Should I Care About BOFs?īOFs allow users to execute code without following Cobalt Strike’s well-defined patterns. The release of this code is less about these techniques themselves, and more about using them as an introduction for writing your own BOFs. You can find the code for that work here. The work I completed implements some basic situational awareness commands. I will also share some code that you can reference for what finalized code might look like. In this post, I will outline some of the less obvious restrictions of BOFs and share my workflow in an effort to assist anyone tasked with writing in this format. This is implemented through what has been termed Beacon Object Files (BOFs). With the release of Cobalt Strike 4.1, a new feature has been added that allows code to be run in a more OPSEC friendly manner.