Thousands of printers at risk of denial of service attacks

Researchers have highlighted a trio of potential attacks against printers that could allow denial of service, information theft, or botnet compromise.

The collection of attacks, labeled Printjack, appeared in a paper from researchers Giampaolo Bella and Pietro Biondi at the Universit`a di Catania and Istituto di Informatica e Telematica in Italy.

The attacks all focus on the 9100 port, which printers commonly use to accept print jobs. Printers frequently expose this port to the open internet, which can render them vulnerable to attack, the paper warns.

"Raw port 9100 printing is massively used worldwide. For example, we observe that it is the default print method that the Common UNIX Printing System (CUPS) leverages, and that CUPS is vastly used in modern Linux distributions and Apple systems," it said. However, it noted that this didn't seem to be the case on Windows systems.

The researchers noted three possible attacks. These include a 'paper DoS', in which attackers send print jobs in an infinite loop until a printer exhausts its paper supply. This attack is effectively a modern version of an old hack in which attackers send an endless loop of paper to a fax machine. The researchers successfully tested the hack on 20 of their own printers using a 12-line Python script.

Another attack threatens the confidentiality of data sent to a printer across the network. The researchers used the Ettercap network traffic interception suite, along with the Wireshark network traffic analysis tool to analyze printer jobs sent across a network, and found that they were sent in plain text. They speculated that an intruder could launch a man in the middle (MITM) attack and intercept that job, potentially putting confidential information at risk.

"Because printing is still common practice today, we cannot fully justify why data stored on a server would normally be protected and, by contrast, data sent off for printing would not," they said. They added that this might put companies in violation of the GDPR privacy regulation.

Finally, Bella and Biondi note the possibility of a botnet-style attack in which printers could be compromised en masse, although they did not test this attack in practice. Instead, they pointed to several known vulnerabilities that allow remote code execution.

Using the Shodan IoT search engine to search for printers with open 9100 ports, researchers found the largest percentage in Germany, with the second biggest collection in Russia, closely followed by France.