CVE-2024-44948 is a vulnerability identified in the Linux kernel's handling of Memory Type Range Registers (MTRRs) on x86 architectures. MTRRs are used to control caching behavior for specific physical memory ranges, with a now-obsolete fixed variant that manages the 640KB to 1MB memory region via dedicated Model-Specific Registers (MSRs). The vulnerability arises because the kernel function mtrr_save_state() fails to verify the presence of the fixed MTRR capability bit before accessing these fixed MTRR MSRs. Historically, all x86 CPUs supporting MTRRs have this capability bit set, so the lack of this check went unnoticed. However, on CPUs lacking this fixed MTRR capability bit, attempts to read the fixed MTRR MSRs cause a General Protection Fault (#GP). Although the fault is handled gracefully by the kernel (the RDMSR fault is caught), it triggers a WARN_ON() kernel warning, which can lead to unnecessary kernel warnings or logs. This issue does not cause a system crash or kernel panic but indicates improper handling of CPU features. The patch involves adding the missing capability check before accessing fixed MTRR MSRs, preventing the #GP and associated warnings on affected CPUs. There are no known exploits in the wild, and the vulnerability primarily affects Linux kernel versions identified by the commit hash 2b1f6278d77c1f2f669346fc2bb48012b5e9495a and similar. No CVSS score has been assigned yet.

For European organizations, the impact of CVE-2024-44948 is relatively limited in terms of direct security consequences. The vulnerability does not allow privilege escalation, code execution, or data leakage. Instead, it causes kernel warnings and potential instability in logging or monitoring systems on specific hardware configurations lacking the fixed MTRR capability bit. This could complicate system diagnostics or obscure other kernel issues due to noisy logs. Organizations running Linux on uncommon or newer x86 CPUs that do not support fixed MTRRs might experience these warnings, potentially leading to increased operational overhead or misinterpretation of system health. However, since the fault is handled gracefully and does not cause crashes or data corruption, the availability and integrity of systems remain intact. The vulnerability is unlikely to be exploited for malicious purposes given the lack of direct security impact and the requirement for specific hardware conditions. Nevertheless, in environments with strict compliance or high-availability requirements, any kernel warnings or anomalies could trigger incident responses or audits, indirectly affecting operational efficiency.

To mitigate this vulnerability, European organizations should prioritize updating their Linux kernel to the patched versions that include the capability check for fixed MTRRs. Specifically, applying the kernel update containing the commit 2b1f6278d77c1f2f669346fc2bb48012b5e9495a or later will resolve the issue. Organizations should verify their hardware inventory to identify systems running on x86 CPUs that might lack the fixed MTRR capability bit, focusing patch deployment accordingly. Additionally, monitoring kernel logs for WARN_ON() messages related to MTRR accesses can help detect affected systems preemptively. For critical systems where kernel updates require extensive testing, temporary mitigation includes suppressing or filtering the specific kernel warnings to reduce noise in monitoring systems, though this does not fix the root cause. Maintaining up-to-date firmware and BIOS versions is also advisable, as CPU microcode updates may influence MTRR behavior. Finally, organizations should incorporate this vulnerability into their patch management and vulnerability assessment processes to ensure timely remediation.