BootHole Vulnerability In Secure Boot Affects Windows and Linux Devices

Heads up all Windows and Linux users! A serious vulnerability potentially exposes your device to cyber attacks. Dubbed BootHole, the vulnerability affects the Secure Boot mechanism of the devices. Consequently, exploiting this flaw allows an attacker to execute arbitrary codes during the boot process.

BootHole Vulnerability Affecting Windows and Linux

Researchers from security firm Eclypsium have caught a vulnerability affecting millions of Linux and Windows systems. Named as BootHole, the vulnerability affects the GRUB2 bootloader empowering these devices.

What Is Secure Boot?

Briefly, the problem exists in the process of device boot. As a standard, PCs, and servers comply with the UEFI Secure Boot standard developed by the UEFI Forum. This Secure Boot standard ensures that the device does not contain any malicious program before it starts. As described by the researchers,

The goal is to prevent malicious code from being introduced into the boot process by cryptographically checking each piece of firmware and software before it is run. Any code not recognized as valid is not executed in the boot process.

This Secure Boot uses Microsoft’s 3rd Party UEFI CA (Certification Authority) letting Microsoft validate and sign the code. Hence, OEMs simply need to enroll the Microsoft 3rd Party UEFI CA to their platforms, thereby letting the non-Microsoft bootloaders to get signed as well.

In the case of Linux, the GRand Unified Bootloader version 2 is the default bootloader. That’s where the researchers found the vulnerability.

About BootHole Vulnerability

Specifically, the researchers at Eclypsium found a buffer overflow vulnerability in GRUB2 that allowed an attacker to bypass Secure Boot. Hence, it became possible for an attacker to execute malicious codes on the target device. At this point, as the code runs from the very beginning, the attackers could gain persistent access to the device.

They describe it as follows,

The vulnerability is a buffer overflow that occurs in GRUB2 when parsing the grub.cfg file. This configuration file is an external file commonly located in the EFI System Partition and can therefore be modified by an attacker with administrator privileges without altering the integrity of the signed vendor shim and GRUB2 bootloader executables. The buffer overflow allows the attacker to gain arbitrary code execution within the UEFI execution environment, which could be used to run malware, alter the boot process, directly patch the OS kernel, or execute any number of other malicious actions.

While the vulnerability primarily targets GRUB2, its impact isn’t limited to Linux only. Rather it also affects Windows. In fact, it’s a threat to all systems using GRUB2 bootloader, or the Secure Boot with the standard Microsoft 3rd Party UEFI CA.

More details about this vulnerability are available in the researchers’ vulnerability report.

What Next?

Following the discovery of this vulnerability affecting millions of devices globally, the researchers followed a responsible disclosure.

As believed, patching this bug requires deploying of new bootloaders whilst revoking the old ones. Hence, they reported the problem to various OS vendors, OEMs, and CERTs.

Consequently, Microsoft has shared a detailed advisory about this problem, along with other vendors like HP, VMware, and Linux Distros. Patches will soon roll out to the individual users accordingly.

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