Locking Down the Multifunction Printer

Most everyone knows networked multifunction printers can pose a dangerous weak link within an enterprise, but not everyone agrees on just how to secure them.

Printer manufacturer Sharp upped the ante recently by adding Solidcore Systems' change control software to its server-powered MX Series printers and multifunction peripherals that run Windows XP Embedded. The software helps stop unauthorized code from running on Sharp devices and prevents unauthorized configuration changes. Sharp previously had relied on antivirus scans to keep the devices clean, but scans and their updates sapped performance and couldn't detect zero-day attacks.

Networked printers connected to the Internet are at risk from the same security threats as servers and desktop machines, says Hiromu Yoshimoto, a member of Sharp's software development department. Sharp implemented the new software on printers at its customer Circle K's convenience stores.

"As the multifunction printers are delivered to various places like convenience stores, the systems can be vulnerable to users installing unauthorized software and applications on the printers," Yoshimoto says. "The printer vendor [wants] to control what software can run on the systems, block unauthorized software from being installed, and limit the patching cycles needed for the printers."

Sharp is just one of several printer vendors that Solidcore is courting with its change control software. "We're in talks with others," says Jim Sarale, vice president of embedded solutions for Solidcore, who says the networked printer can be a weak link in the network. "We are one big attack away from these [devices] not getting forgotten" anymore, he says. "All it would take is a zero-day attack or a well intentioned but unauthorized change to one of the devices."

Embedded change control software such as Solidcore's S3 Control Embedded is the next wave of security for these devices, says Sharp's Yoshimoto. "With change control installed as a foundation of these systems, other security measures such as antivirus are no longer needed," he says.

Printer vulnerabilities haven't traditionally been top enterprise security priorities, but they are getting more attention as organizations realize how these boxes can get hacked. A researcher recently found what he called a cross-site printing vulnerability -- a way to remotely hack printers using JavaScript to use the printer as a conduit for spam. (See Printers Could Be Vulnerable to Spam.)

Meanwhile, Robert Graham, CEO of Errata Security, notes that it's unlikely that attackers would purposely target a printer. "However, more and more of them contain Windows XP Embedded. This means that hackers might break into it thinking it's a normal Windows desktop computer without even realizing it's a printer," he says. "Thus, while normally I would suggest that only paranoid organizations [such as DOD and intelligence organizations] worry about their printers, it has now become something that all organizations need to worry about."

Change control software in general isn't necessarily the solution, Graham argues. "The problem with change control software is that they either all allow too much change, which means an update will introduce a bug that disables the device, or too little [and] it gets hacked into anyway. There is no 'just right' amount of change," he says.

Graham recommends hardening embedded devices like printers by doing things like turning off default accounts. "Most embedded operating systems come with default passwords that allow anybody to connect to the device," he says.

Security researcher Brendan O'Connor, who at the 2006 Black Hat USA briefings uncovered key vulnerabilities in Xerox's printers, is also skeptical of adding another layer of software to secure printers. (See Print at Your Own Risk.)

"If we take a step back and look at the real problem, the issue is that software has security vulnerabilities," he says. "Does it make sense to add more software to mitigate the issue or to fix the buggy code that's already there? I would argue the latter makes more sense."

O'Connor says multifunction device makers just need to do what the rest of the software industry must do: fix the software.

Solidcore's Sarale, meanwhile, says his company's software only allows the authorized "image" of the printer software to execute, and it also replaces the need for AV scans that printers such as Sharp had used previously. "Blocking worms and Trojans is one of the things [the S3 software] does," he says.

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