CVE-2021-47462 is a vulnerability in the Linux kernel's memory policy subsystem, specifically within the mbind() system call implementation. The issue arises from improper validation of memory policy flags related to NUMA (Non-Uniform Memory Access) balancing. A commit (bda420b98505) introduced a new bit in MPOL_MODE_FLAGS to support NUMA balancing with migration on fault among multiple bound nodes. However, the validation logic for allowed flag combinations was only applied in do_set_mempolicy(), not in mbind(), allowing illegal combinations of MPOL_F_NUMA_BALANCING and MPOL_LOCAL flags to be passed. This leads to access of uninitialized memory in the __mpol_equal() function, which compares memory policies, causing undefined behavior and potential kernel panics. The vulnerability was discovered and reported by syzbot, a kernel fuzzing tool, which triggered a kernel panic due to uninitialized memory usage detected by Kernel Memory Sanitizer (KMSAN). The root cause is that the flag validation was moved to sanitize_mpol_flags() but mbind() did not use this function, resulting in unchecked invalid flag combinations. Exploitation of this flaw could cause system instability, crashes, or denial of service due to kernel panics. The vulnerability affects Linux kernel versions containing the problematic commit and was patched by ensuring mbind() also sanitizes the flags properly. There is no evidence of active exploitation in the wild. The vulnerability requires local access to invoke mbind() with crafted flags, and it does not appear to allow privilege escalation or remote code execution directly. However, it undermines kernel memory safety and stability, which is critical for system reliability.

For European organizations, the impact of CVE-2021-47462 primarily concerns system stability and availability. Linux is widely used in enterprise servers, cloud infrastructure, and embedded systems across Europe. A kernel panic triggered by this vulnerability could cause unexpected downtime, disrupt critical services, and impact business continuity. Organizations relying on NUMA architectures for performance optimization in data centers or HPC environments may be more exposed if they use affected kernel versions. Although this vulnerability does not directly lead to data breaches or privilege escalation, denial of service in critical infrastructure or cloud platforms could have cascading effects on operations and service delivery. Additionally, organizations with stringent uptime requirements, such as financial institutions, telecommunications providers, and public sector entities, could face operational risks. The lack of known exploits reduces immediate threat, but the vulnerability should be addressed promptly to maintain system integrity and prevent potential exploitation in targeted attacks or by insider threats.

1. Apply the official Linux kernel patches that fix CVE-2021-47462 as soon as possible. Ensure kernel versions are updated to include the sanitize_mpol_flags() check in mbind(). 2. For organizations using custom or long-term support kernels, backport the patch or upgrade to a supported kernel version containing the fix. 3. Implement strict access controls to limit which users or processes can invoke mbind() system calls, reducing the attack surface. 4. Monitor kernel logs and system behavior for signs of kernel panics or memory sanitizer warnings that could indicate attempts to trigger this vulnerability. 5. In environments using NUMA balancing features, review and audit memory policy configurations to ensure they do not use unsupported or experimental flags. 6. Employ kernel hardening and runtime integrity monitoring tools to detect anomalous system calls or memory corruption attempts. 7. Coordinate with cloud providers or third-party vendors to confirm that underlying Linux kernels are patched if using managed services. 8. Maintain an incident response plan to quickly recover from potential denial of service caused by kernel panics.