Attackers have learned that vulnerabilities can hide in the gaps: gaps between components of a system or gaps in a process or procedure. A researcher last week at DEF CON in Las Vegas showed that device drivers — the small utility applications that allow particular pieces of hardware to work with an operating system — can bridge critical gaps for legitimate hardware and malicious hackers alike.
Jesse Michael and Mickey Shkatov, both of Eclypsium, based their research on the fact that while drivers allow communication between software and hardware, they also facilitate communication between the so-called user mode and the OS kernel. And since they operate at the permission level of the kernel, they indeed can be very powerful tools.
Malware that exploits drivers isn't new, and the simple fact that a driver vulnerability is being exploited isn't novel. There have been numerous campaigns, most recently last year's LoJax malware ascribed to Sednit, which employed driver exploits.
In Michael and Shkatov's research, though, they found more than 40 drivers from at least 20 vendors — including every major BIOS vendor — had vulnerabilities. More important than the basic number was that every vulnerable driver they discovered was certified by Microsoft, nullifying one of the most basic protection mechanisms in place for Windows systems.
Each of the vulnerabilities found facilitate privilege escalation from Ring 3 to Ring 0: at this privilege level, attackers can perform kernel virtual memory access, physical memory access, MMIO access, MSR access, control register access, PCI device access, SMBUS access, and much more.
In their presentation, the researchers showed several attack scenarios, from exploiting a driver that exists on the system but is not yet loaded, to malware that brings its own drivers with counterfeit signatures. In each of these cases, the drivers, once loaded, can carry malicious kernel patches, illicit reads and writes of specific memory locations, modifications to Unified Extensible Firmware Interface (UEFI) and device firmware, and other actions that would facilitate complete system takeover.
The researchers pointed out that an attacker would need access to the system prior to exploiting a driver vulnerability. Once the initial infection is accomplished, however, the driver exploit could be a very persistent method for privilege escalation and exploit execution.
Michael and Shkatov first reported their findings to Microsoft and other vendors. Microsoft and some of the affected vendors already have issued patches for known issues, while others have not responded to the researchers.
Whether a particular vendor has patched their drivers or not, Michael and Shkatov pointed out, Windows will still allow older, unpatched drivers to run on a system, leaving risk in place until the latest version of Windows 10 is running with its new drivers.