CVE-2023-52463 is a vulnerability in the Linux kernel's efivarfs filesystem, which is responsible for interfacing with EFI variables stored in firmware. The vulnerability arises because when the firmware does not support the SetVariable function at runtime, the efivarfs is mounted as read-only (RO) to prevent modification attempts. However, the kernel does not properly enforce this read-only restriction when the filesystem is remounted, allowing it to be remounted as read-write (RW) despite the lack of SetVariable support. This improper permission check leads to a NULL pointer dereference and a kernel crash (kernel oops) when an attempt is made to write to efivarfs, as demonstrated by the crash logs involving the efi-updatevar utility. The root cause is that the kernel does not verify the mount flags during remount operations, permitting unsafe RW remounts. The fix involves adding a .reconfigure() function to the filesystem operations to check requested mount flags and deny any remount attempts that are not RO if the firmware lacks runtime SetVariable support. This vulnerability can cause denial of service (DoS) by crashing the kernel, potentially impacting system stability and availability. It affects Linux kernel versions containing the vulnerable efivarfs implementation, particularly those prior to the patch that enforces proper mount flag checks during remounts.

For European organizations, this vulnerability poses a risk primarily of denial of service due to kernel crashes triggered by improper remounting of efivarfs. Systems relying on EFI variables and running vulnerable Linux kernel versions could experience unexpected reboots or downtime if an attacker or misconfigured process attempts to remount efivarfs as read-write when the firmware does not support SetVariable at runtime. This could disrupt critical services, especially in environments using Linux servers for infrastructure, cloud services, or embedded systems. While exploitation requires local access to attempt remounting efivarfs, the impact on availability could be significant in sensitive or high-availability environments. Confidentiality and integrity impacts are minimal since the vulnerability leads to a crash rather than arbitrary code execution or privilege escalation. However, repeated crashes could be leveraged as part of a broader attack to degrade system reliability or availability.

1. Apply the latest Linux kernel updates that include the patch for CVE-2023-52463 to ensure the .reconfigure() function properly enforces read-only remount restrictions on efivarfs when SetVariable is unsupported. 2. Restrict local user permissions to prevent unauthorized remounting of efivarfs. Only trusted administrators should have the capability to remount system filesystems. 3. Monitor system logs for attempts to remount efivarfs as read-write and investigate any such events promptly. 4. For critical systems, implement kernel crash monitoring and automated recovery mechanisms to minimize downtime in case of unexpected kernel oops. 5. In environments where firmware does not support runtime SetVariable, consider disabling or limiting use of efivarfs where feasible to reduce attack surface. 6. Conduct regular firmware and kernel compatibility audits to ensure that kernel features align with firmware capabilities, preventing misconfigurations that could trigger this vulnerability.