23 Using Networking Service with Netcat

• Understanding Netcat (nc) for Network Testing
  • nc (Netcat) is a low-level tool for sending and receiving network data.
  • Commonly used for manual service testing and network diagnostics.
  • Works without the complex processing of web browsers or other services.
• Setting Up a Netcat Server
  • nc -l <port> starts a listener (server) on a given port.
  • Example: nc -l 54321 listens for connections on port 54321.
  • Servers require an IP address and an open port to accept connections.
• Connecting a Client to the Server
  • nc <server_IP> <port> connects a client to a Netcat server.
  • Example: nc 192.168.118.100 54321 establishes a connection.
  • Once connected, text sent from one machine appears on the other.
• Understanding Ports and Services
  • Services use ports to determine which application handles data.
  • Standard ports include 80 (HTTP), 443 (HTTPS), and 22 (SSH).
  • Unregistered ports (above 1024) can be used for custom services.
• Using Netcat for Remote Command Execution
  • nc -l -p <port> -e /bin/bash redirects input to a bash shell.
  • Example: nc -l -p 54321 -e /bin/bash allows remote command execution.
  • This method can be exploited for unauthorized remote access.
• Preventing Netcat Exploits
  • Restricting open ports prevents unauthorized remote connections.
  • Firewalls and security policies should block unnecessary services.
  • Running nc -l -p <port> in a loop (e.g., via Python) creates persistent backdoors.

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