One of the most shocking parts of the
recently discovered spying network Equation Group is its mysterious module designed to reprogram or reflash a computer hard drive's firmware with malicious code. The Kaspersky researchers who uncovered this said its ability to subvert hard drive firmware—the guts of any computer—"surpasses anything else" they had ever seen.

The hacking tool, believed to be a product of the NSA, is significant because subverting the firmware gives the attackers God-like control of the system in a way that is stealthy and persistent even through software updates. The module, named "nls_933w.dll", is the first of its kind found in the wild and is used with both the EquationDrug and GrayFish spy platforms Kaspersky uncovered.

It also has another capability: to create invisible storage space on the hard drive to hide data stolen from the system so the attackers can retrieve it later. This lets spies like the Equation Group bypass disk encryption by secreting documents they want to seize in areas that don't get encrypted.

Kaspersky has so far uncovered 500 victims of the Equation Group, but only five of these had the firmware-flashing module on their systems. The flasher module is likely reserved for significant systems that present special surveillance challenges. Costin Raiu, director of Kaspersky's Global Research and Analysis Team, believes these are high-value computers that are not connected to the internet and are protected with disk encryption.

Here's what we know about the firmware-flashing module.

How It Works

Hard drive disks have a controller, essentially a mini-computer, that includes a memory chip or flash ROM where the firmware code for operating the hard drive resides.

When a machine is infected with EquationDrug or GrayFish, the firmware flasher module gets deposited onto the system and reaches out to a command server to obtain payload code that it then flashes to the firmware, replacing the existing firmware with a malicious one. The researchers uncovered two versions of the flasher module: one that appears to have been compiled in 2010 and is used with EquatinoDrug and one with a 2013 compilation date that is used with GrayFish.

The Trojanized firmware lets attackers stay on the system even through software updates. If a victim, thinking his or her computer is infected, wipes the computer's operating system and reinstalls it to eliminate any malicious code, the malicious firmware code remains untouched. It can then reach out to the command server to restore all of the other malicious components that got wiped from the system.

Even if the firmware itself is updated with a new vendor release, the malicious firmware code may still persist because some firmware updates replace only parts of the firmware, meaning the malicious portions may not get overwritten with the update. The only solution for victims is to trash their hard drive and start over with a new one.

The attack works because firmware was never designed with security in mind. Hard disk makers don't cryptographically sign the firmware they install on drives the way software vendors do. Nor do hard drive disk designs have authentication built in to check for signed firmware. This makes it possible for someone to change the firmware. And firmware is the perfect place to conceal malware because antivirus scanners don't examine it. There's also no easy way for users to read the firmware and manually check if it's been altered.

The firmware flasher module can reprogram the firmware of more than a dozen different hard drive brands, including IBM, Seagate, Western Digital, and Toshiba.

"You know how much effort it takes to land just one firmware for a hard drive? You need to know specifications, the CPU, the architecture of the firmware, how it works," Raiu says. The Kaspersky researchers have called it "an astonishing technical accomplishment and is testament to the group's abilities."

Once the firmware is replaced with the Trojanized version, the flasher module creates an API that can communicate with other malicious modules on the system and also access hidden sectors of the disk where the attackers want to conceal data they intend to steal. They hide this data in the so-called service area of the hard drive disk where the hard disk stores data needed for its internal operation.

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