Bettercap: TCP Proxy Upstream Server

G5 Cyber Security

4 months ago

TL;DR

This guide shows you how to set up an upstream server for Bettercap’s TCP proxy, allowing it to forward traffic through a specified host. This is useful for tunnelling traffic or using Bettercap with remote servers.

Setting Up the Upstream Server

Understand the Concept: Bettercap’s TCP proxy normally intercepts and handles connections locally. An upstream server lets you send that intercepted traffic to another host (your chosen server) for further processing or routing.
Configure Bettercap: You’ll use Bettercap’s proxy.upstream option to define the server address and port.
```
bettercap -cfg proxy.upstream 192.168.1.100:8080
```
Replace 192.168.1.100:8080 with the actual IP address and port of your upstream server.
Start Bettercap in Proxy Mode: Launch Bettercap with the TCP proxy enabled.
```
bettercap -proxy on
```
Verify Traffic Forwarding:
- Connect to a website or service while Bettercap is running.
- On your upstream server, check if you’re receiving the forwarded traffic (e.g., using netstat, tcpdump, or your server’s logging).

Advanced Configuration

Using a Different Interface: If you want Bettercap to listen on a specific network interface for proxy connections:
```
bettercap -iface eth0 -proxy on
```
Replace eth0 with your desired interface.
Specifying the Upstream Server in a Config File: Edit Bettercap’s configuration file (usually located at ~/.config/bettercap/bettercap.conf) and add or modify the following line:
```
proxy.upstream = 192.168.1.100:8080
```
Handling HTTPS Traffic: Bettercap can proxy HTTPS traffic, but you’ll need to configure it correctly.
- Ensure your upstream server is capable of handling SSL/TLS connections (e.g., using a reverse proxy like Nginx or Apache).
- Consider using the proxy.ssl option in Bettercap if needed, but be aware of potential certificate issues and man-in-the-middle risks.

Troubleshooting

Connection Refused: Check that your upstream server is running and listening on the specified port. Also, ensure there are no firewalls blocking the connection between Bettercap and the server.
Traffic Not Forwarded: Verify that Bettercap is correctly intercepting traffic (using netstat or packet capture tools). Check your upstream server logs for any errors.
SSL/TLS Errors: If you’re proxying HTTPS traffic, ensure your upstream server has a valid SSL certificate and that Bettercap is configured to handle it properly.