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

The nxc smb command is a robust tool designed for penetration testing and exploiting SMB (Server Message Block) servers. It allows cybersecurity professionals to identify vulnerabilities, enumerate resources, and perform various operations on SMB servers. This command is particularly useful for security assessments and penetration testing exercises that aim to discover weaknesses in SMB implementations within a network.

Use case 1: Search for Valid Domain Credentials by Trying Out Every Combination in the Specified Lists of Usernames and Passwords

Code:

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

Motivation:

Cybersecurity professionals often need to identify weak credentials as part of security assessments. By trying various combinations of usernames and passwords, they can determine if any accounts on the SMB server are protected by weak or easily guessable passwords, which could be exploited by malicious actors.

Explanation:

• 192.168.178.2: Specifies the IP address of the target SMB server.
• -u path/to/usernames.txt: Provides the path to a file containing a list of potential usernames.
• -p path/to/passwords.txt: Points to a file with a compilation of potential passwords.

Example Output:

[+] Found valid credentials:
    Username: admin, Password: welcome123
    Username: guest, Password: guestpass
[-] No valid credentials found for remaining combinations

Use case 2: Search for Valid Credentials for Local Accounts Instead of Domain Accounts

Code:

nxc smb 192.168.178.2 -u path/to/usernames.txt -p path/to/passwords.txt --local-auth

Motivation:

In several environments, SMB servers may have local accounts that are distinct from domain accounts. Testing these accounts for weak credentials is crucial, especially when domain accounts are well-guarded, but local accounts may be overlooked in security policies.

Explanation:

• 192.168.178.2: Target SMB server’s IP address.
• -u path/to/usernames.txt: File path to a potential usernames list.
• -p path/to/passwords.txt: File path to a potential passwords list.
• --local-auth: Tells the tool to authenticate only against local accounts, not domain accounts.

Example Output:

[+] Valid local account credentials discovered:
    Username: localuser, Password: localpass123
[-] Remaining combinations did not yield valid credentials

Use Case 3: Enumerate SMB Shares and the Specified Users’ Access Rights to Them on the Target Hosts

Code:

nxc smb 192.168.178.0/24 -u username -p password --shares

Motivation:

Understanding the layout of shared resources on SMB servers and the associated permissions can help pinpoint potential areas for data leakage or privilege escalation. By enumerating these details, analysts can assess if any sensitive data is exposed or if any shares have been misconfigured.

Explanation:

• 192.168.178.0/24: A CIDR notation indicating a range of IP addresses to be scanned for shares.
• -u username: Specifies a username for authenticating the scan.
• -p password: Provides the password associated with the given username.
• --shares: Instructs the tool to enumerate the available SMB shares.

Example Output:

[+] SMB Shares for 192.168.178.4:
    Share: HR-Documents, Access: read-only
    Share: IT-Configs, Access: read-write
[+] SMB Shares for 192.168.178.5:
    No accessible shares for the provided credentials.

Use Case 4: Enumerate Network Interfaces on the Target Hosts, Performing Authentication via Pass-the-Hash

Code:

nxc smb 192.168.178.30-45 -u username -H NTLM_hash --interfaces

Motivation:

Enumerating network interfaces with authenticated sessions, especially using the pass-the-hash technique, is useful in scenarios where direct credentials are not available, but a hash is retrievable. This allows testers to gain insights into the network configuration and connected devices, which could be vital for lateral movement in a penetration test.

Explanation:

• 192.168.178.30-45: A range of IP addresses to be assessed for network interfaces.
• -u username: Username used to authenticate.
• -H NTLM_hash: Specifies the NTLM hash used for pass-the-hash authentication instead of a plaintext password.
• --interfaces: Command option to specifically enumerate available network interfaces.

Example Output:

[+] Network Interfaces on 192.168.178.32:
    Interface 1: eth0, IP: 192.168.178.32, MAC: 00:A0:C9:75:43:11
    Interface 2: wlan0, IP: 192.168.178.33, MAC: 00:A0:C9:75:43:12

Use Case 5: Scan the Target Hosts for Common Vulnerabilities

Code:

nxc smb path/to/target_list.txt -u '' -p '' -M zerologon -M petitpotam

Motivation:

Automated vulnerability scanning using known exploits, such as Zerologon and PetitPotam, helps in quickly identifying whether SMB servers are susceptible to these significant security issues. This allows for prompt remediation to mitigate the potential impact.

Explanation:

• path/to/target_list.txt: A text file containing a list of IP addresses or hostnames to be examined for vulnerabilities.
• -u '': An empty user parameter indicating anonymous or unauthenticated scans.
• -p '': An empty password parameter for unauthenticated scans.
• -M zerologon, -M petitpotam: Modules specifically targeting known vulnerabilities, enabling targeted scanning.

Example Output:

[+] Vulnerability Check on 192.168.178.42:
    Vulnerability: Zerologon - Vulnerable
    Vulnerability: PetitPotam - Not Vulnerable
[-] No vulnerabilities found on remaining hosts

Use Case 6: Attempt to Execute a Command on the Target Hosts

Code:

nxc smb 192.168.178.2 -u username -p password -x command

Motivation:

Executing commands remotely on an SMB server can help demonstrate the extent of control or access possible due to existing vulnerabilities or misconfigurations. This showcases the potential real-world impact of the discovered security weaknesses.

Explanation:

• 192.168.178.2: Specifies the IP address of the target SMB server for command execution.
• -u username: Username for authentication.
• -p password: Password corresponding to the username.
• -x command: The command to be executed on the target host.

Example Output:

[+] Command execution on 192.168.178.2:
    Output: 'Directory listing successful: C:\Users\Admin\Desktop'

Conclusion

The nxc smb command is a versatile tool for security professionals aiming to test and exploit SMB servers. Through the use cases discussed, we’ve seen its capabilities ranging from credential discovery to vulnerability scanning and remote command execution. Each use case serves a distinct purpose in a security assessment, underscoring the importance of regular penetration testing and timely remediation of identified vulnerabilities.