Even if you don't have more than one operating system installed, your PC has a boot-loader, a software component first executed by the system BIOS, which decides which operating system to boot with. This also lets users toggle between different run-levels or configurations of the same OS. The GRUB2 boot-loader is deployed across billions of computers, servers, and pretty much any device that uses a Unix-like operating system. Cybersecurity researchers with Oregon-based firm Eclypsium, discovered a critical vulnerability with GRUB2 that can compromise a device's operating system. They named the vulnerability BootHole. This is the same firm behind last year's discovery of the Screwed Drivers vulnerability. It affects any device that uses the GRUB2 boot-loader, including when combined with Secure Boot technology.

BootHole exploits a design flaw with two of the key components of GRUB2, bison, a parser generator, and flex, a lexical analyzer. Eclypsium discovered that these two can have "mismatched design assumptions" that can lead to buffer overflow. This buffer overflow can be exploited to execute arbitrary code. Devices with modern UEFI and Secure Boot enabled typically wall off even administrative privileged users off from tampering with boot processes, however, in case of BootHole, the boot-loader parses a configuration file located in the EFI partition of the boot device, which can be modified by any user (or malicious process) that has admin privileges. Thankfully, patched versions of GRUB2 are already out, and the likes of SUSE have started distributing it for all versions of SUSE Linux. Expect practically every other *nix vendor, server manufacturer, to release patches to their end-users. Find a technical run-down of the vulnerability in this PDF by Eclypsium.

Cybersecurity research firm Eclypsium published a report titled "Screwed Drivers," chronicling a critical flaw in the design of modern device driver software from over 40 hardware manufacturers, which allows malware to gain privilege from Ring 3 to Ring 0 (unrestricted hardware access). The long list of manufacturers publishing drivers that are fully signed and approved by Microsoft under its WHQL program, includes big names such as Intel, AMD, NVIDIA, AMI, Phoenix, ASUS, Toshiba, SuperMicro, GIGABYTE, MSI, and EVGA. Many of the latter few names are motherboard manufacturers who design hardware monitoring and overclocking applications that install kernel-mode drivers into Windows for Ring-0 hardware-access.

As part of its study, Eclypsium chronicles three classes of privilege-escalation attacks exploiting device drivers, RWEverything, LoJax (first UEFI malware), SlingShot. At the heart of these are the exploitation of the way Windows continues to work with drivers with faulty, obsolete, or expired signing certificates. Eclypsium hasn't gone into the nuts-and-bolts of each issue, but has briefly defined the three in a DEF CON presentation. The firm is working by several of the listed manufacturers on mitigations and patches, and is under embargo to put out a whitepaper. RWEverything is introduced by Eclypsium as a utility to access all hardware interfaces via software. It works in user-space, but with a one-time installed signed RWDrv.sys kernel-mode driver, acts as a conduit for malware to gain Ring-0 access to your machine. LoJax is an implant tool that uses RWDrv.sys to gain access to the SPI flash controller in your motherboard chipset, to modify your UEFI BIOS flash. Slingshot is an APT with its own malicious driver that exploits other drivers with read/write MSR to bypass driver signing enforcement to install a rootkit.