Blobrunner

Blobrunner

Blobrunner is a C program that loads binary files (shellcode, PE files, or raw blobs) into memory and executes them. It's useful for reverse engineering, malware analysis, and shellcode testing.

What Blobrunner Does

1. Reads a binary file from disk
2. Allocates executable memory using VirtualAlloc
3. Copies the file contents into that memory
4. Executes the code at a specified offset

This bypasses traditional file execution, making it valuable for:

• Testing shellcode without creating executable files
• Analyzing malware behavior in a controlled environment
• Running PE files in memory for debugging
• Reverse engineering exercises

Compilation

Prerequisites

• Visual Studio Code with C/C++ extension
• MinGW-w64 or Visual Studio compiler (Windows)

Steps

1. Create a new C/C++ project in VS Code
2. Copy the source code from references/blobrunner.c
3. Build the project

Note: The only modification from the original code is line 10 (Windows header inclusion).

Usage

blobrunner.exe <inputfile> [options]

Required Arguments

• <inputfile>: Path to the binary file to load and execute

Optional Arguments

Examples

Basic execution:

blobrunner.exe shellcode.bin

Execute at specific offset:

blobrunner.exe malware.exe --offset 0x1000

Run without pause (for automation):

blobrunner.exe payload.bin --nopause

Trigger JIT exception for debugging:

blobrunner.exe shellcode.bin --jit

Verbose debugging:

blobrunner.exe sample.bin --debug --offset 0x401000

How It Works

Memory Allocation

Blobrunner uses VirtualAlloc with these flags:

• 0x3000 = MEM_COMMIT | MEM_RESERVE
• 0x40 = PAGE_EXECUTE_READWRITE

This creates executable memory where the binary is loaded.

Execution Methods

32-bit:

• Uses inline assembly jmp shell_entry to jump directly to the code

64-bit:

• Creates a suspended thread with CreateThread
• Allows you to set breakpoints before resuming
• Resumes with ResumeThread

JIT Mode

When --jit is used:

1. Memory is allocated as executable
2. First byte's execute permission is removed with VirtualProtect
3. This triggers an exception when execution reaches that point
4. Useful for debugging and analysis

Safety Warnings

⚠️ Use with extreme caution:

• Only run trusted binaries - Malicious code will execute with your privileges
• Use in a VM or sandbox - Never run unknown binaries on your main system
• Understand the code - Review the source before using
• --nopause is dangerous - Execution happens immediately without warning

Common Use Cases

1. Shellcode Testing

# Test shellcode without creating an executable file
blobrunner.exe shellcode.bin --debug

2. PE File Analysis

# Load a PE file and jump to its entry point
blobrunner.exe suspicious.exe --offset 0x1000 --debug

3. Malware Analysis

# Run malware in memory with JIT exception for debugging
blobrunner.exe malware.bin --jit --debug

4. Offset Discovery

# Test different offsets to find the correct entry point
blobrunner.exe blob.bin --offset 0x0
blobrunner.exe blob.bin --offset 0x100
blobrunner.exe blob.bin --offset 0x200

Troubleshooting

"Unable to open file"

• Check the file path is correct
• Ensure the file exists and is readable
• Try using absolute paths

"Error Creating thread" (64-bit)

• Run as administrator if needed
• Check if the binary is valid
• Verify the offset is within file bounds

Nothing happens after execution

• The code may have exited silently
• Use --debug for more information
• Check if the code requires specific conditions

Source Code Reference

The complete source code is available in references/blobrunner.c. Key sections:

• process_file(): Reads file and allocates memory
• execute(): Handles execution (different for 32/64-bit)
• main(): Parses arguments and orchestrates execution

Related Tools

• x64dbg/x32dbg: For detailed debugging
• Process Hacker: For monitoring memory allocations
• Cuckoo Sandbox: For automated malware analysis
• Ghidra: For static analysis before execution

Next Steps

1. Compile the tool following the steps above
2. Start with simple shellcode to test basic functionality
3. Use a VM for any unknown binaries
4. Enable debug mode when learning
5. Review the source code to understand the mechanics

Remember: This tool executes arbitrary code in memory. Always use it responsibly and in appropriate environments.