Discover printers during an internal penetration testing engagement using Nmap and other Recon…

Here is the comprehensive guide on how to discover printers during an internal penetration testing engagement using Nmap and other Recon techniques.

Printers are high-value targets because they often run outdated firmware, use default credentials, and frequently cache Active Directory domain credentials.

1. Port Scanning with Nmap (The Fastest Method)

Printers rely on specific operational protocols. You can isolate them quickly by targeting these exact ports across the internal subnet.

A. Quick Port Sweep

nmap -p 9100,515,631,2501,445,161,80,443 --open 192.168.16.0/24

nmap -p 9100,515,631,2501,445,161,80,443 --open 192.168.16.0/24

Port Breakdown:

• 9100 (JetDirect): The most common raw printing port.
• 515 (LPD): Line Printer Daemon protocol.
• 631 (IPP): Internet Printing Protocol.
• 161 (SNMP): Used for printer management and configuration status.
• 80 / 443: The web management interface (Web GUI) of the printer.

B. Service and OS Fingerprinting

nmap -sV -O -p 9100,631,161 --script=banner 192.168.16.0/24

nmap -sV -O -p 9100,631,161 --script=banner 192.168.16.0/24

• Why this works: This command grabs service banners and attempts OS detection. The output will explicitly name vendors like HP, Canon, Xerox, Ricoh, or Brother.

2. SNMP Reconnaissance (The Goldmine)

Printers almost always have SNMP (Simple Network Management Protocol) enabled, and they often use the default community string public. This exposes critical device details.

A. Nmap SNMP Scripts

nmap -sU -p 161 --script=snmp-sysdescr,snmp-interfaces 192.168.16.0/24

nmap -sU -p 161 --script=snmp-sysdescr,snmp-interfaces 192.168.16.0/24

• Result: Since SNMP runs over UDP (-sUThis script queries the system description to return the exact model number, firmware version, and device name.

B. Fast Subnet Sweeping with onesixtyone

onesixtyone -c communities.txt 192.168.16.0/24

onesixtyone -c communities.txt 192.168.16.0/24

• Why this works: It brute-forces community strings simultaneously across the range, instantly identifying active printers responding to public or private.

3. Advanced Discovery Techniques

A. Automated Web Screenshots via EyeWitness

Once you find active web servers on ports 80/443, extract those IPs to a file (targets.txt) and run:

eyewitness --web -f targets.txt

eyewitness --web -f targets.txt

• Result: It compiles an HTML report with visual screenshots of the login pages, making it easy to identify printer control panels at a glance.

B. Exploiting mDNS / Bonjour (Local Broadcasts)

Printers constantly broadcast their presence to Windows and macOS devices using mDNS (Multicast DNS). You can sniff out these broadcasts using Nmap:

nmap -p 5353 --script=dns-service-discovery 192.168.16.0/24

nmap -p 5353 --script=dns-service-discovery 192.168.16.0/24

Next Steps After Identifying Printers

1. Default Credentials: Search Google for the specific model's manual to find default logins (e.g., admin/admin, admin/password, admin/blank).
2. Credential Harvesting: Check the printer's LDAP/SMTP settings. If "Save Credentials" is enabled for network scanning, you can modify the server IP to point to your Kali machine and intercept the domain service account credentials.
3. PRET (Printer Exploitation Toolkit): If port 9100 is open, use PRET to connect to the device. It allows you to read printer memory, dump print jobs, or access the underlying file system.