How to Use the Command 'nxc vnc' (with Examples)

The ’nxc vnc’ command is a powerful tool designed for penetration testing and exploiting VNC (Virtual Network Computing) servers. This command can be used to test for vulnerabilities, discover valid login credentials, and perform various actions on a remote system. It’s a useful utility for security professionals who need to evaluate the security posture of VNC servers. Below are some specific use cases with examples demonstrating how to leverage this command effectively.

Use case 1: Searching for Valid Credentials

Code:

nxc vnc 192.168.178.2 -u path/to/usernames.txt -p path/to/passwords.txt

Motivation: In penetration testing, one of the primary goals is to gain unauthorized access to a target system with valid credentials. This example demonstrates how you can brute force login attempts using specified lists of usernames and passwords. It attempts to find the correct combination that allows access to the VNC server.

Explanation:

• nxc vnc: Initiates the command for targeting a VNC server.
• 192.168.178.2: The IP address of the target VNC server that you are attempting to penetrate.
• -u path/to/usernames.txt: Specifies the file path to the list of usernames to try. This list is iterated through to test each username.
• -p path/to/passwords.txt: Specifies the file path to the list of passwords to try. This list is paired with the usernames in a brute force manner to find valid credentials.

Example Output:

Trying username: admin, password: 1234...
Trying username: admin, password: admin...
Login successful with username: admin, password: admin123!

Use case 2: Avoiding Rate Limiting with VNC-Sleep

Code:

nxc vnc 192.168.178.2 -u path/to/usernames.txt -p path/to/passwords.txt --vnc-sleep 10

Motivation: Many VNC servers implement rate-limiting features to prevent brute force attacks by temporarily locking accounts or blocking IP addresses after several failed login attempts. This example illustrates how to introduce delays between login attempts to circumvent such protections.

Explanation:

• nxc vnc: Specifies that the ’nxc’ command will interact with VNC servers.
• 192.168.178.2: Target VNC server’s IP address.
• -u path/to/usernames.txt: Provides the path to the usernames list for testing access.
• -p path/to/passwords.txt: Provides the path to the passwords list for the brute force attempt.
• --vnc-sleep 10: Introduces a sleep interval of 10 seconds between each login attempt, reducing the likelihood of triggering rate-limiting mechanisms on the server.

Example Output:

Trying username: admin, password: guest, please wait...
Sleeping for 10 seconds...
Trying username: guest, password: guest, please wait...
Sleeping for 10 seconds...

Use case 3: Taking a Screenshot on the Remote System

Code:

nxc vnc 192.168.178.2 -u username -p password --screenshot --screentime 10

Motivation: In certain scenarios, gaining visual access to the screen of a VNC server can provide vital information for security assessments. This example shows how to take a screenshot of the remote system’s display, giving insight into active sessions or running applications.

Explanation:

• nxc vnc: The command for interacting with VNC servers.
• 192.168.178.2: The specific VNC server’s IP address for connection and interaction.
• -u username: Supplies a valid username to authenticate against the VNC server.
• -p password: Supplies the corresponding valid password.
• --screenshot: Flag to instruct the command to capture a screenshot of the current display on the VNC server.
• --screentime 10: Specifies that the command should wait 10 seconds after logging in before taking the screenshot to ensure everything is loaded and visible.

Example Output:

Authentication successful!
Taking screenshot in 10 seconds...
Screenshot saved as 'vnc_screenshot_192.168.178.2.png'.

Conclusion:

The ’nxc vnc’ command provides a robust set of features for testing and exploiting VNC servers, from trying multiple credential combinations to handling rate limits, and even capturing screenshots of the remote system. These examples illustrate practical applications of the command, showcasing its versatility for security assessments and penetration testing of VNC environments. As always, ethical guidelines and legal permissions should govern the use of such tools.