With their own dedicated processor and operating system, LTE/3G modems built into new business laptops and tablets could be a valuable target for hackers by providing a stealthy way to maintain persistent access to an infected device.
In a presentation Saturday at the DEF CON security conference in Las Vegas, researchers Mickey Shkatov and Jesse Michael from Intel's security group demonstrated how a malware program installed on a computer could rewrite the firmware of a popular Huawei LTE modem module that's included in many devices.
The module runs a Linux-based OS, more specifically a modification of Android, that is completely independent from the computer's main operating system. It's connected to the computer through an internal USB interface, which means that it could be instructed to emulate a keyboard, mouse, CD-ROM drive, network card, or other USB device. Those would appear connected to the primary OS.
The main problem found by the Intel researchers was that the update process for the modem's firmware was insecure, lacking a cryptographic signature verification. This allowed them to create a malicious firmware image that could be written through the Windows update utility provided by the vendor.
The malicious firmware could be flashed by a malicious program that already runs on the computer, or by users themselves if an attacker tricks them into thinking that a new update is available.
If successful, the attack would provide a way to reinfect the main OS even if it is reinstalled. Moreover, the rogue firmware could be modified to ignore any subsequent firmware update requests, leaving the user with no option to recover from such a compromise, except for taking his laptop or tablet apart and pulling out the infected modem module.
Huawei has addressed the issue and the module now performs a secure boot, preventing the use of unauthorized firmware images, the researchers said, adding that the company has been very responsive and great to work with.
There is a platform risk with these modems and other components that provide independent execution environments where malware can survive OS wiping and which are not visible to antivirus and other security programs. That's why secure software updates are really important, the researchers said.