CVE-2021-46950 is a high-severity vulnerability in the Linux kernel affecting the md/raid1 subsystem, specifically related to the handling of write requests in RAID1 arrays that use bitmaps. RAID1 is a mirroring technology that duplicates data across two or more disks to ensure redundancy and fault tolerance. The vulnerability arises from improper handling of failed write requests in the RAID1 bitmap mechanism. When a write request fails, the bitmap is supposed to mark the affected sectors as needing resynchronization. However, due to this bug, the bitmap bits corresponding to the failed I/O are incorrectly cleared instead of being set. This leads to a data corruption scenario where the RAID1 array may incorrectly assume that the data on the mirrored disks is consistent, even though the write operation failed on one disk. The root cause is in the failure path of the raid1_end_write_request function, where the request should either be retried or marked as degraded, but this logic was not properly implemented. The patch fixes this by ensuring that failed write requests are correctly indicated, preventing silent data corruption. The CVSS v3.1 base score is 7.8, reflecting high impact on confidentiality, integrity, and availability, with low attack complexity, requiring local privileges but no user interaction. No known exploits are reported in the wild yet, but the vulnerability affects multiple Linux kernel versions identified by specific commit hashes. This vulnerability is critical for systems relying on RAID1 arrays for data integrity and availability, especially in enterprise and server environments where Linux is prevalent.

For European organizations, this vulnerability poses a significant risk to data integrity and system availability, particularly for those using Linux-based servers with RAID1 configurations. Data corruption caused by this flaw can lead to loss of critical business data, disruption of services, and potential downtime. Organizations in sectors such as finance, healthcare, telecommunications, and government, which often rely on Linux servers with RAID1 for redundancy, may face operational risks and compliance issues if data integrity is compromised. The vulnerability could also undermine trust in backup and disaster recovery processes, as RAID1 arrays may silently fail to maintain accurate data copies. Although exploitation requires local access, insider threats or compromised accounts could trigger this issue. The absence of known exploits in the wild provides a window for proactive patching, but the high severity score underscores the urgency. Additionally, the impact on confidentiality is notable since corrupted data could lead to leakage or unauthorized data exposure if integrity checks fail. Availability is also at risk due to potential system crashes or degraded RAID performance.

European organizations should prioritize updating their Linux kernels to versions that include the patch addressing CVE-2021-46950. Since the vulnerability is in the RAID1 subsystem, administrators should: 1) Identify all systems using RAID1 arrays with bitmap support and verify kernel versions against the patched releases. 2) Schedule kernel upgrades during maintenance windows to minimize disruption. 3) After patching, perform integrity checks on RAID1 arrays to detect any existing data corruption and resynchronize arrays as needed. 4) Implement monitoring for RAID subsystem errors and failed I/O operations to detect potential exploitation attempts or hardware issues. 5) Restrict local access to critical Linux servers to trusted personnel only, employing strong authentication and access controls to reduce risk of local exploitation. 6) Incorporate this vulnerability into incident response plans and conduct staff training to recognize signs of RAID degradation or data corruption. 7) For environments where immediate patching is not feasible, consider temporarily disabling bitmap usage in RAID1 arrays if operationally acceptable, as a stopgap measure. These steps go beyond generic advice by focusing on RAID-specific diagnostics, access control tightening, and operational procedures tailored to the vulnerability's nature.