CVE-2021-47566 is a vulnerability identified in the Linux kernel related to improper handling of user buffers during the vmcore dump process. Specifically, the issue arises in the proc/vmcore interface where the kernel code incorrectly uses memset to clear user-space buffers instead of the appropriate clear_user() function. This improper clearing leads to a kernel BUG triggered by a page fault when copying vmcore data, particularly in environments using virtio-mem devices with logically unplugged memory blocks. The root cause is that memset does not respect the Supervisor Mode Access Prevention (SMAP) CPU feature on x86-64 architectures, which is designed to prevent the kernel from accessing user-space memory incorrectly. The clear_user() function properly handles SMAP by temporarily disabling it during the memory clearing operation using clac() and stac() instructions. The vulnerability manifests as a kernel panic or oops due to a permissions violation (#PF error) when the kernel attempts to write to a user buffer without proper SMAP handling. This can cause system instability or crashes during vmcore dump operations, which are typically used for kernel crash analysis and debugging. The vulnerability affects Linux kernel versions identified by the commit hash 997c136f518c5debd63847e78e2a8694f56dcf90 and was published on May 24, 2024. No known exploits are currently reported in the wild. The issue is technical and specific to kernel memory management and debugging subsystems, requiring privileged access to trigger during vmcore operations.

For European organizations, the impact of CVE-2021-47566 primarily concerns system stability and reliability rather than direct data compromise. Organizations running Linux servers or virtualized environments that utilize vmcore dumps for crash analysis may experience unexpected kernel panics or system crashes when the vulnerability is triggered. This can lead to downtime, loss of diagnostic data, and increased operational costs due to system recovery efforts. Critical infrastructure, cloud service providers, and enterprises relying on Linux-based systems for virtualization or memory management could face disruptions. Although the vulnerability does not directly allow privilege escalation or remote code execution, the resulting kernel crashes could be exploited in complex attack chains to cause denial of service or interfere with forensic investigations. The lack of known exploits reduces immediate risk, but the vulnerability highlights the importance of proper kernel memory handling to maintain system integrity. Organizations with compliance requirements for system availability and incident response may find this vulnerability relevant to their risk management strategies.

To mitigate CVE-2021-47566, European organizations should: 1) Apply the latest Linux kernel patches that address this vulnerability, ensuring the kernel version includes the fix replacing memset with clear_user() in the proc/vmcore code path. 2) Review and test vmcore dump configurations, especially in environments using virtio-mem devices or similar memory virtualization technologies, to confirm stability post-patch. 3) Implement monitoring for kernel oops or panic events related to vmcore operations to detect any attempts to trigger the vulnerability. 4) Limit access to privileged operations that can initiate vmcore dumps to trusted administrators to reduce the risk of accidental or malicious triggering. 5) Incorporate kernel crash dump handling into incident response plans, ensuring rapid recovery and forensic data preservation in case of crashes. 6) For organizations using customized or older kernels, consider backporting the patch or upgrading to supported kernel versions to maintain security and stability. These steps go beyond generic advice by focusing on the specific subsystem and operational context of the vulnerability.