CVE-2020-26541: 
Linux Kernel vulnerability analysis and mitigation

CVE-2020-26541 is a security vulnerability discovered in the Linux kernel through version 5.8.13, affecting the Secure Boot Forbidden Signature Database (dbx) protection mechanism. The vulnerability was disclosed on October 2, 2020, and specifically impacts the implementation in certs/blacklist.c and certs/system_keyring.c files (NVD).

The vulnerability stems from improper enforcement of the Secure Boot Forbidden Signature Database (dbx) protection mechanism. The dbx contains revoked signatures and keys that were previously approved for UEFI Secure Boot. The issue specifically occurs when EFICERTX509_GUID entries are contained in the dbx, as these entries were being skipped instead of being properly processed (LKML). The vulnerability has been assigned a CVSS v3.1 Base Score of 6.5 (Medium) with vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:R/S:U/C:H/I:H/A:H (NVD).

The vulnerability could allow an attacker to bypass UEFI Secure Boot restrictions, potentially compromising the secure boot chain. This could enable the execution of unauthorized code during the boot process, affecting the system's security integrity (Ubuntu).

The vulnerability has been fixed in various Linux distributions through security updates. For example, Red Hat has released patches for Red Hat Enterprise Linux for Real Time 8 and related products (Red Hat). Ubuntu has also provided fixes for affected versions, including Ubuntu 20.04 LTS (focal) and 21.04 (hirsute) (Ubuntu).