CVE-2024-26674 is a vulnerability in the Linux kernel related to the handling of machine check exceptions (MCEs) during memory error injection tests on kernels version 6.4 and later. The issue arises from a change in the exception fixup mechanism used for the {get,put}_user() functions, which are responsible for safely accessing user-space memory from kernel space. Specifically, a commit replaced the fixup macro _ASM_EXTABLE_UA() with _ASM_EXTABLE(), changing the fixup type from EX_TYPE_UACCESS to EX_TYPE_DEFAULT. This change caused the kernel to panic on certain machine check exceptions instead of recovering gracefully. The vulnerability manifests as a kernel panic triggered by an unrecoverable data load error in kernel space, which occurs because the kernel no longer correctly identifies user-space memory access exceptions, leading to fatal local machine checks. The problem does not appear in kernels 6.3 and earlier, indicating it was introduced in or after version 6.4. The fix involved reverting to the original _ASM_EXTABLE_UA() macro for exception fixups in {get,put}_user(), restoring the kernel's ability to handle in-kernel MCEs properly. This vulnerability is technical and low-level, involving kernel memory access and exception handling mechanisms, and it can cause system instability or denial of service through kernel panics under specific conditions involving hardware errors and memory error injections.

For European organizations, the impact of CVE-2024-26674 primarily involves system stability and availability. Linux is widely used across Europe in servers, cloud infrastructure, embedded systems, and critical infrastructure. A kernel panic caused by this vulnerability can lead to unexpected system crashes, resulting in downtime and potential disruption of services. Organizations relying on Linux kernels version 6.4 or later, especially those performing memory error injection testing or operating in environments prone to hardware errors, may experience increased risk of denial-of-service conditions. While this vulnerability does not directly expose confidentiality or integrity risks, the availability impact can be significant for critical systems such as telecommunications, finance, healthcare, and industrial control systems. Additionally, recovery from kernel panics may require manual intervention or automated failover mechanisms, increasing operational overhead. Since exploitation requires specific hardware error conditions and triggers, the risk of widespread exploitation is low, but the vulnerability highlights the importance of kernel robustness in handling hardware faults.

To mitigate CVE-2024-26674, European organizations should: 1) Apply the latest Linux kernel patches that revert the exception fixup mechanism to _ASM_EXTABLE_UA() for {get,put}_user() functions, ensuring proper handling of machine check exceptions. 2) Avoid deploying unpatched Linux kernels version 6.4 or later in production environments, especially where hardware error injection testing or unstable hardware is involved. 3) Implement robust hardware monitoring and error detection to identify and address underlying hardware faults that could trigger machine check exceptions. 4) Use kernel crash dump and logging tools to capture detailed information on kernel panics for faster diagnosis and remediation. 5) Employ high-availability and failover configurations to minimize service disruption in case of kernel panics. 6) Coordinate with hardware vendors to ensure microcode updates and firmware are current, reducing the likelihood of hardware errors. 7) For environments requiring memory error injection testing, conduct tests in isolated staging environments to prevent impact on production systems.