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1. #Cobalt strike beacon hx flagging Patch#
2. #Cobalt strike beacon hx flagging code#
3. #Cobalt strike beacon hx flagging windows#

The above possibility is the impetus for this blog post.

#Cobalt strike beacon hx flagging code#

The adversary’s code that lives in a process has the same rights and ability to examine and change code as the security product that installed itself there. The downside of the above instrumentation method is that it’s also suscpetible to tamper and attack by an adversary. It’s still common in a lot of security technologies today. This method of instrumentation is popular because it’s easy-ish to implement, well understood, and was best practice in security products for a very long time.

#Cobalt strike beacon hx flagging Patch#

There are a lot of different ways to hook, but one of the most common is to patch the first instructions in a function-of-interest to jump to the vendor’s code, do the analysis, execute the patched over instructions, and resume the function just after the patch. (b) from the product DLL: installs hooks into certain APIs of interest. (a) load a security product DLL into the process space The process for this instrumentation looks like this:

#Cobalt strike beacon hx flagging windows#

I say a lot, because certainly some actions are not easy to see via today’s instrumentation methods.Ī popular method to instrument Windows endpoints is userland hooking. A well-instrumented endpoint provides a defense team and an automated security solution with the potential to react to or have visibility into a lot of events on a system. The &beacon_inline_execute function is Aggressor Script's entry point to run a BOF file.When I think about defense in the current era, I think of it as a game of instrumentation and telemetry. A BOF is a good place to implement a lateral movement technique, an escalation of privilege tool, or a new reconaissance capability. You'll likely want to use Aggressor Script to run your finalized BOF implementations within Cobalt Strike. These decorations provide the compiler with the needed hints to pass arguments and generate the right call instruction. Keywords, such as WINAPI and DECLSPEC_IMPORT are important. When you declare function prototypes for Dynamic Function Resolution, pay close attention to the decorators attached to the function declaration. The above code makes DFR calls to DsGetDcNameA and NetApiBufferFree from NETAPI32. Here's an example BOF that uses DFR and looks up the current domain: #include ĭECLSPEC_IMPORT DWORD WINAPI NETAPI32$DsGetDcNameA(LPVOID, LPVOID, LPVOID, LPVOID, ULONG, LPVOID) ĭECLSPEC_IMPORT DWORD WINAPI NETAPI32$NetApiBufferFree(LPVOID) ĭwRet = NETAPI32$DsGetDcNameA(NULL, NULL, NULL, NULL, 0, &pdcInfo) īeaconPrintf(CALLBACK_OUTPUT, "%s", pdcInfo->DomainName) When this process fails, Cobalt Strike will refuse to execute the BOF and tell you which function it couldn't resolve. This convention provides Beacon the information it needs to explicitly resolve the specific function and make it available to your BOF file before it runs. Another option is to use Dynamic Function Resolution (DFR).ĭynamic Function Resolution is a convention to declare and call Win32 APIs as LIBRARY$Function. You have the option to use these to resolve Win32 APIs you wish to call. GetProcAddress, LoadLibraryA, GetModuleHandle, and FreeLibrary are available within BOF files. BeaconOutput is an internal Beacon API to send output to the operator. It's the function that's called by inline-execute and arguments are passed to it. The function go is similar to main in any other C program. Use inline-execute in Beacon to run the BOF.īeacon> inline-execute /path/to/hello.o these are argumentsīeacon.h contains definitions for several internal Beacon APIs. The above commands will produce a hello.o file. The same exploit, built as a BOF, is īeaconPrintf(CALLBACK_OUTPUT, "Hello World: %s", args)

A UAC bypass privilege escalation Reflective DLL implementation may weigh in at 100KB+. They run inside of a Beacon process and are cleaned up after the capability is done.īOFs are also very small. These tools rely on an OPSEC expensive fork&run pattern that involves a process create and injection for each post-exploitation action. Cobalt Strike already has tools to use PowerShell. One of the key roles of an command&control platform is to provide ways to use external post-exploitation functionality.

Way to rapidly extend the Beacon agent with new post-exploitation features. A Beacon Object File (BOF) is a compiled C program, written to a convention that allows it to execute within a Beacon process and use internal Beacon APIs.