how hackers hide (Intro to Beacon Object Files - with Empire C2!)
Source: YouTube · John Hammond · published Jul 18, 2025 · 33:08
This video provides a comprehensive guide to Beacon Object Files (BOFs), which are lightweight, modular code components that extend C2 framework capabilities 0:00. BOFs were first introduced with Cobalt Strike in 2021 and allow loading and executing native code in memory at runtime while maintaining stealth 1:06.
Key Takeaways:
• BOFs are compiled Microsoft COFF object files that enable functionality extension without bloating beacon code or spawning detectable child processes 0:00
• Developing a BOF requires C/C++ code compiled with specific flags (e.g., -c using MinGW) to create an object file rather than a full executable 2:25
• BOFs use dynamic function resolution to call Windows API functions by prefixing symbols with library names followed by a dollar sign 13:32
• BOFs can be integrated with C2 frameworks like Empire through proper YAML configuration and file placement in the appropriate directories 16:40
BOFs offer advantages over alternatives like shellcode (difficult to write), DLLs (more overhead), and .NET assemblies (requires entire CLR) while providing a lightweight, platform-agnostic solution for extending C2 capabilities 31:02.
Sources:
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Say that you are developing malware for all the right reasons, of course, maybe for your job as a red teamer or cyber threat emulation offensive security specialist and you are building an implant like an endpoint agent that runs on a victim computer and operates as a beacon that just calls back to a command and control server or framework like a C2. And it makes sense for you to want that beacon to be as lightweight as possible. At its core, it should really just handle communication with the C2 server. But you'll still want extra capability. You want it to do more than just that, like continue post exploitation or persistence or exfiltration or whatever. You don't want to bloat up the beacon code. And you shouldn't really spawn or invoke some other external or child process cuz you may v…