By Robert McMillan
IDG News Service
16 April 2008
For years, hackers have focused on finding bugs in computer software
that give them unauthorised access to computer systems, but now there's
another way to break in: hack the microprocessor.
Researchers at the University of Illinois at Urbana-Champaign
demonstrated how they altered a computer chip to grant attackers
back-door access to a computer. It would take a lot of work to make this
attack succeed in the real world, but it would be virtually
To launch its attack, the team used a special programmable processor
running the Linux operating system. The chip was programmed to inject
malicious firmware into the chip's memory, which then allows an attacker
to log into the machine as if he were a legitimate user. To re-program
the chip, researchers needed to alter only a tiny fraction of the
processor circuits. They changed 1,341 logic gates on a chip that has
more than 1 million of these gates in total, said Samuel King, an
assistant professor in the university's computer science department.
"This is like the ultimate back door," said King. "There were no
software bugs exploited."
King demonstrated the attack on Tuesday at the Usenix Workshop on
Large-Scale Exploits and Emergent Threats, a conference for security
researchers held in San Francisco.
His team was able to add the back door by reprogramming a small number
of the circuits on a LEON processor running the Linux operating system.
These programmable chips are based on the same Sparc design that is used
in Sun Microsystems' midrange and high-end servers. They are not widely
used, but have been deployed in systems used by the International Space
In order to hack into the system, King first sent it a specially crafted
network packet that instructed the processor to launch the malicious
firmware. Then, using a special login password, King was able to gain
access to the Linux system. "From the software's perspective, the packet
gets dropped... and yet I have full and complete access to this
underlying system that I just compromised," King said.
The researchers are now working on tools that could help detect such a
malicious processor, but there's a big problem facing criminals who
would try to reproduce this type of attack in the real world. How do you
get a malicious CPU onto someone's machine?
This would not be easy, King said, but there are a few possible
scenarios. For example, a "mole" developer could add the code while
working on the chip's design, or someone at a computer assembly plant
could be paid off to install malicious chips instead of legitimate
processors. Finally, an attacker could create a counterfeit version of a
PC or a router that contained the malicious chip.
"This is not a script kiddie attack," he said. "It's going to require an
entity with resources."
Though such a scenario may seem far-fetched, the US Department of
Defense (DoD) is taking the issue seriously. In a February 2005 report,
the DoD's Defense Science Board warned of the very attack that the
University of Illinois researchers have developed, saying that a shift
toward offshore integrated circuit manufacturing could present a
There are already several examples of products that have shipped with
malicious software installed. In late 2006, for example, Apple shipped
Video iPods that contained the RavMonE.exe virus.
"We're seeing examples of the overall supply chain being compromised,"
King said. "Whether or not people will modify the overall processor
designs remains to be seen."
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