How 'Postcript' Exploits Networked Printers

Network printer exploits are like old dogs learning new tricks, according to a security researcher with Ruhr University.

In his upcoming Black Hat presentation, Exploiting Network Printers, Jens Muller, Ruhr University chair for network and data security will delve into an analysis of printer attacks, in which he discovered 20 printer models were all vulnerable to at least one of the same attacks that he tested. Muller will also disclose unusual ways the Internet is enabling network printer attacks via advanced cross-site printing techniques.

The vulnerability, Muller says, stems from the 35-year-old PostScript programming language, which has connected printers to end-users for decades, even as technology evolved from the parallel printer cable, to the USB stick, to networked printers, and today to the cloud.

"Before, printers used parallel cables and having PostScript wasn't a problem." Muller says. "But now, the printer manufacturers are still using PostScript and they can easily be exploited remotely."

PostScript: An Industry Standard 

The PostScript programming language is an industry standard for network printers and its use is ubiquitous. But despite attackers ability to exploit this language, printer manufacturers have largely looked the other way, he says. Instead, manufacturers put the onus on network administrators to place the printers inside the network, where the devices are presumed to be protected from outside threats.

Even today, he notes, manufacturers do not seem to realize that attackers can drill into networked printers by way of the Internet.

On the networking side, network administrators tend to view their connected printers as nothing more than a printing device, as opposed to a potential vector of attack, he says, noting that the end result is that network admins may not think it's important to secure network printers.

Some of the attacks Muller has tested include a denial of service attack that damaged eight of the 20 printers he was testing. One new issue to emerge is the ability to set a printer back to its factory defaults by taking control of the printer remotely. Other printer attacks range from stealing print jobs containing sensitive information to pilfering system files.

Work Arounds

One potential solution to the problem, Muller says, is to corral all the connected printers and put them on a separate network with a print server. The downside: it would require a network administrator to oversee two networks, which, he says, could be difficult for midsized companies and result in the additional costs of installing and monitoring a second firewall.

"What CISOs should really do is ask themselves do they really need a device connected," Muller says. "It may make sense not to connect the printer to the cloud."

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