![]() It also supports applying custom File Attributes to help mask a binary as legitimate:įile Attributes on the generated loader are copied from CMD.EXEĪ fake code signing signature applied by ScareCrow via LimeLighter integration. To make things even more interesting, ScareCrow uses a golang port of the tool LimeLighter to spoof code signing certificates on the binary/dll files it generates. As a red team operator, it’s important to understand as much as you can about your tools and techniques. I won’t go into more detail here, you can read more about how this works on GitHub repository, which I highly recommend. Using syscalls is a great way to evade hooks and behavioral monitoring, and even though it already removed the EDR hooks, there are other solutions that may still detect these API call events such as Event Tracing for Windows, which ScareCrow will also bypass. From there, it leverages syscalls to load, decrypt and run your shellcode in-memory. Windows Defender is pretty good about detecting the shellcode from Cobalt Strike’s beacon, so this step is crucial.Īfter executing the generated loader, it will bypass the EDR’s hooks on NTDLL.DLL by loading a clean copy of NTDLL.DLL (as well as kernel32.dll and kernelbase.dll) from disk and replacing it with the hooked one in your process space, thus removing the EDR’s hooks entirely. ScareCrow takes your raw shellcode and encrypts it using AES, which is beneficial to avoid static detection on-disk when a defense product scans the loader you generated. In short, we can generate some raw shellcode from the software of our choice (Cobalt Strike, Metasploit, PoshC2, etc) and pass it to the homie to get a loader back that will implement some common EDR evasion techniques. ![]() You can read all about how it works on its README page here. ScareCrow is described as a “payload creation framework”. Read on, comrade! Hey You, Meet ScareCrow (unhooking the hooked functions, loading a clean copy of NTDLL from the disk that’s unhooked, using syscalls to evade detection, etc). ![]() It used to be possible to thwart this EDR DLL injection by simply applying a process creation mitigation policy that would only allow DLLs signed by Microsoft to be loaded into your process space, however, most defense products have this Microsoft signing and we can no longer leverage this clever trick.įortunately, there are still several ways around this. If you create a new child process, open a file, inject code – they can see it in real-time and even stop it before it’s allowed to happen. When you spawn a new process on a Windows machine, the EDR will load it’s own DLL into your process space, and place funciton hooks on these NTDLL.DLL functions, allowing it to monitor relevant process behaviors by essentially being a man-in-the-middle of every request that process makes to the Windows API. When a process starts on Windows, one of the DLLs loaded is NTDLL.DLL, which contains a myriad of Windows API calls that applications use to interface with the operating system and it’s components (Processes / Files / etc). Most EDR products these days now resort to user-mode API hooking to monitor your behaviors. In an effort to increase the stability of the Windows Kernel, KPP was invented, which restricts what internal structures kernel drivers are allowed to modify, restricting these tools to user-mode monitoring techniques, which makes life a little easier for those of us trying to evade them! These kernel-mode drivers that attempted to patch the Windows Kernel to intercept or monitor activity would frequently cause stability issues by doing unspeakable things. Check out the Read More section at the bottom of this post for more in-depth posts regarding EDR functionality.īack in the “old times”, before Microsoft enforced Kernel Patch Protection (KPP), anti-virus software would typically load a kernel-mode driver to monitor behavior outside of user-mode, where all of your normal applications run and reside. In an effort to keep this post short and sweet, this will be a brief explanation of a much more complex topic, but it’s good to understand how EDR is detecting your payloads and behaviors, to help you understand the steps we take to avoid it’s prying eyes. Understanding the EDR Behavior Monitoring Strategy We deploy a lot of Cobalt Strike, and I wanted to write up a short blog post on how you can quickly deploy a beacon (or your own choice of raw shellcode) on an endpoint protected by one of these solutions. During red team engagements, we frequently encounter EDR solutions.
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