Vulnerability resides in the GRUB2 bootloader, which, if exploited, could potentially let attackers bypass the Secure Boot feature and gain high-privileged persistent and stealthy access to the targeted systems. The attack allows hackers to execute malicious code even before the operating system boots, making it difficult for security software to detect the presence of malware or remove it. Experts at Eclypsium have contacted related industry entities, including OS vendors and computer manufacturers, to help them patch the issue.
Source: https://thehackernews.com/2020/07/grub2-bootloader-vulnerability.html