'Smart' Batteries May Leave Laptop Users Vulnerable, Researcher Says

If you're looking for security vulnerabilities on you laptop, there's a new spot to check: the battery.

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The embedded controllers on laptop batteries are hackable, a researcher says, because some manufacturers -- including Apple -- do not change the passwords that prevent changes to the smart battery system's firmware according to an investigation of Apple laptop batteries carried out by security researcher Charlie Miller.

The data, which will be presented by veteran security researcher Charlie Miller at the Black Hat Conference next week, found that Apple batteries have two fixed passwords that allow the company to update the laptop component's firmware. Unfortunately, those passwords also make the smart battery system hackable.

Miller, a senior security consultant at Accuvant, took apart the batteries, identified their components, and found that batteries sold by Apple have a default password to unlock them and another discoverable password to allow access to the firmware.

With those two passwords known, eavesdropping on the communications between the laptop and the battery -- and running your own programs -- are both possible, he says.

"I definitely completely destroyed that first and most important layer of defense," Miller says. "The main brains of the operation is this chip, and I can control that now."

In a white paper on the research, Miller described the smart battery system as consisting of three chips, two of which protect against potential electrical problems. In addition, each battery cell has a thermal cutoff fuse that physically cuts power to and from the cell if its temperature rises too high.

The batteries are shipped in a locked down, or "sealed," mode, but the default password in the battery manufacturer's specification allows the battery to be unsealed, Miller says. In By reverse-engineering a MacBook battery update, Miller found the password that gives full access to the system.

While Miller limited his investigation to MacBook batteries, the research may apply to other non-Apple laptops as well. He tested a single off-market battery, however, and found that the manufacturer used a non-default password, limiting his ability to hack the system.

Miller had no problem bricking the batteries, but he failed in his original plan: to make laptop batteries overheat or even explode.

"I can definitely make it so the battery doesn't respond anymore," he says. "I did that seven times already."

In the end, Miller found he could rewrite the smart battery firmware to make the battery respond as an attacker wanted. He theorized that a program could be placed on the battery to allow malware to survive a clean install of a system, making the battery one more place to hide persistent attacks.

While Miller's research did not result in any "explosive" vulnerabilities, the research shows that investigating hardware components can bear fruit, even for software hackers, says Joe Grand, principal electrical engineer for Grand Idea Studio and a noted hardware hacker.

"The one thing that Charlie's work really exemplifies is this blending of hardware and software," Grand says. "To do hardware hacking, you don't have to be a hardware guy anymore, you can be a software guy. All these embedded systems are just small software systems, small computers."

It's unlikely that attackers will start focusing on laptop batteries, however. There's no real profit motive in bricking laptop batteries, says Grand.

"Whether attacking a battery is a worthwhile endeavor or not remains to be seen," he says. "Most malicious people are going to do things that make them money."

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