Building The Mac Office

Attackers could turn your laptop's battery into a useless brick, or worse, overcharge it to the point where it starts a fire.

That warning comes by way of security expert Charlie Miller, who said that he's successfully reverse-engineered Apple laptop "smart batteries," enabling him to reprogram their embedded controllers. Miller, who's a researcher at consultancy Accuvant, plans to document his research at next month's Black Hat conference in Las Vegas.

According to Miller's Black Hat talk description, "being able to control the working smart battery and smart battery host may be enough to cause safety issues, such as overcharging or fire." Notably, when the lithium-ion batteries used in laptops overheat, they can rupture, causing injuries. On the other hand, well-manufactured batteries also include numerous safety features, such as the ability to shut down in the event of overheating, as well as circuit interrupters designed to prevent overcharging or undercharging.

In his forthcoming talk, Miller plans to will demonstrate how to modify the firmware used by Apple smart batteries, disable their anti-tampering checksum, and reprogram the battery firmware using "a simple API," which he plans to release publicly. While Miller's research focused on MacBook, MacBook Pro, and MacBook Air laptops from Apple--with whom he's already shared the results of his research--he suspects that Windows laptop batteries would be susceptible to firmware attacks.

Miller reverse-engineered Apple's battery firmware after the company issued a related firmware update in 2009. From there, he discovered the default password used to secure batteries, and from there, he learned how to read the values from that firmware and alter how the battery firmware interacts with the laptop. To date, Miller said he's successfully bricked seven Mac laptops via battery firmware hacks.

Interestingly, however, reprogramming the battery firmware could also allow an attacker to introduce persistent malware into the laptop. "You could put a whole hard drive in, reinstall the software, flash the BIOS, and every time it would reattack," Miller told Forbes.com. "There would be no way to eradicate or detect it other than removing the battery."

Despite the apparent threat vector, battery firmware offers essential functionality, providing giving users precise readings of a laptop's remaining charge, operating time, and estimated recharge time, while also allowing the battery to control the voltage and current being provided by a charger.

But how feasible are attacks against battery firmware? Offering some perspective, Paul Ducklin, head of technology for Sophos in the Asia Pacific region, said in a blog post that when it comes to reprogramming controllers with field-updatable firmware, laptop batteries aren't the only option. Indeed, an attacker could also target "the motherboard itself, your wireless card, your 3G modem, network card, graphics device, storage devices, and much more," he said.

To address the Apple laptop battery firmware vulnerability, Miller plans to release a utility called "Caulkgun" that will allow Apple users to change their laptop battery passwords. On the upside, the utility would prevent an attacker from exploiting an Apple battery pack's embedded controller. On the downside, it would block any Apple patches, performance enhancements, or security updates from updating the battery's firmware, unless the user first restored the battery's default password.

The vendors, contractors, and other outside parties with which you do business can create a serious security risk. Here's how to keep this threat in check. Also in the new, all-digital issue of Dark Reading: Why focusing solely on your own company's security ignores the bigger picture. Download it now. (Free registration required.)