Process Injection

The process-inject block in Malleable C2 profiles shapes injected content and controls process injection behavior for the Beacon payload. It also controls the behavior of Beacon Object Files (BOF) execution within the current beacon.

process-inject {
     # set how memory is allocated in a remote process for injected content
     set allocator "VirtualAllocEx";
 
     # set how memory is allocated in the current process for BOF content
     set bof_allocator "VirtualAlloc";
     set bof_reuse_memory "true";
 
     # shape the memory characteristics for injected and BOF content
     set min_alloc "16384";
     set startrwx "true";
     set userwx    "false";
 
     # transform x86 injected content
     transform-x86 {
          prepend "\x90\x90";
     }
 
     # transform x64 injected content
     transform-x64 {
          append "\x90\x90";
     }
 
     # determine how to execute the injected code
     execute {
          CreateThread "ntdll.dll!RtlUserThreadStart";
          SetThreadContext;
          RtlCreateUserThread;
     }
}

The process-inject block accepts several options that control the process injection process in Beacon:

Option	Example	Description
allocator	VirtualAllocEx	The preferred method to allocate memory in the remote process. Specify VirtualAllocEx or NtMapViewOfSection. The NtMapViewOfSection option is for same-architecture injection only. VirtualAllocEx is always used for cross-arch memory allocations.
bof_allocator	VirtualAlloc	The preferred method to allocate memory in the current process to execute a BOF. Specify VirtualAlloc, MapViewOfFile, or HeapAlloc.
bof_reuse_memory	true	Reuse the allocated memory for subsequent BOF executions otherwise release the memory. Memory will be cleared when not in use. If the available amount of memory is not large enough it will be released and allocated with the larger size.
min_alloc	4096	Minimum amount of memory to request for injected or BOF content.
startrwx	false	Use RWX as initial permissions for injected or BOF content. Alternative is RW. When BOF memory is not in use the permissions will be set based on this setting.
userwx	false	Use RWX as final permissions for injected or BOF content. Alternative is RX.

The transform-x86 and transform-x64 blocks pad content injected by Beacon. These blocks support two commands: prepend and append.

The prepend command inserts a string before the injected content. The append command adds a string after the injected content. Make sure that prepended data is valid code for the injected content’s architecture (x86, x64). The c2lint program does not have a check for this.

The execute block controls the methods Beacon will use when it needs to inject code into a process. Beacon examines each option in the execute block, determines if the option is usable for the current context, tries the method when it is usable, and moves on to the next option if code execution did not happen. The execute options include:

Option	x86->x64	x64->x86	Notes
CreateThread			Current process only
CreateRemoteThread		Yes	No cross-session
NtQueueApcThread
NtQueueApcThread-s			This is the “Early Bird” injection technique. Suspended processes (e.g., post-ex jobs) only.
RtlCreateUserThread	Yes	Yes	Risky on XP-era targets; uses RWX shellcode for x86 -> x64 injection.
SetThreadContext		Yes	Suspended processes (e.g., post-ex jobs) only.

The CreateThread and CreateRemoteThread options have variants that spawn a suspended thread with the address of another function, update the suspended thread to execute the injected code, and resume that thread. Use [function] “module!function+0x##” to specify the start address to spoof. For remote processes, ntdll and kernel32 are the only recommended modules to pull from. The optional 0x## part is an offset added to the start address. These variants work x86 -> x86 and x64 -> x64 only.

The execute options you choose must cover a variety of corner cases. These corner cases include self injection, injection into suspended temporary processes, cross-session remote process injection, x86 -> x64 injection, x64 -> x86 injection, and injection with or without passing an argument. The c2lint tool will warn you about contexts that your execute block does not cover.

 

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