Description

Detects the usage of unencrypted Telnet connections in Java applications using the Apache Commons Net library. This is a security concern because Telnet transmits data in plaintext, potentially exposing sensitive information to network eavesdropping and man-in-the-middle attacks.

Detection Strategy

• Check if the Apache Commons Net Telnet library (org.apache.commons.net.telnet) is imported in the code

• Look for instantiations of TelnetClient objects and track their variable names

• Search for connect() method calls on identified TelnetClient variables within the same scope

• Report a vulnerability when a TelnetClient object is used to establish a connection

Vulnerable code example

import org.apache.commons.net.telnet.TelnetClient;

public class VulnerableTelnetExample {
    public void connectToServer(String host) {
        try {
            // Vulnerable: Using telnet which transmits data in plaintext
            TelnetClient telnet = new TelnetClient();
            telnet.connect(host, 23);...

✅ Secure code example

import com.jcraft.jsch.JSch;
import com.jcraft.jsch.Session;

public class SecureConnectionExample {
    public void connectToServer(String host, String user, String password) {
        try {
            // Secure: Using SSH instead of telnet for encrypted communication
            JSch jsch = new JSch();...