CVE-2021-47351 is a concurrency vulnerability found in the UBIFS (UBI File System) component of the Linux kernel. UBIFS is a file system designed for flash memory devices, commonly used in embedded systems and IoT devices. The vulnerability arises from race conditions between extended attribute (xattr) operations: specifically, between xattr_set, xattr_get, and listxattr. These operations manage metadata attributes associated with files. Due to the lack of proper synchronization, concurrent execution of these operations can lead to assertion failures, memory corruption, and stale or inconsistent xattr values. The root cause is the absence of a suitable read-write lock to serialize write operations on xattrs, allowing unsafe concurrent modifications. The fix implemented involves introducing a new read-write lock in the ubifs_inode structure to serialize write operations on xattrs, while still permitting concurrent read operations, similar to the ext4 file system approach. This correction prevents race conditions without significantly impacting read performance. The vulnerability was publicly disclosed and fixed in May 2024, with no known exploits in the wild reported to date. The affected versions correspond to specific Linux kernel commits prior to the patch. This issue primarily affects systems using UBIFS on Linux kernels that have not incorporated the fix. Since UBIFS is specialized for flash memory devices, the vulnerability is most relevant to embedded Linux systems, industrial devices, and IoT platforms that rely on UBIFS for storage management.

For European organizations, the impact of CVE-2021-47351 depends on their use of Linux-based embedded systems or devices employing UBIFS on flash memory. Potential impacts include system instability due to memory corruption or assertion failures, which can lead to unexpected crashes or data loss. Stale or corrupted extended attributes can affect the integrity and reliability of file metadata, potentially disrupting applications that rely on accurate xattr data for security policies, configuration, or auditing. While this vulnerability does not directly enable remote code execution or privilege escalation, the resulting instability could be exploited by attackers with local access to cause denial of service or to corrupt critical data. Industries in Europe that heavily use embedded Linux devices—such as automotive, manufacturing automation, telecommunications infrastructure, and critical IoT deployments—may face operational risks if devices are unpatched. Furthermore, given the increasing regulatory focus on cybersecurity and data integrity in Europe (e.g., NIS2 Directive), organizations must ensure their embedded systems are secure to maintain compliance and avoid operational disruptions.

To mitigate CVE-2021-47351, European organizations should: 1) Identify all embedded Linux devices and systems using UBIFS, particularly those running kernel versions prior to the fix. 2) Apply the official Linux kernel patches that introduce the read-write lock serialization for xattr write operations. This may require updating the kernel on embedded devices or applying vendor-provided firmware updates. 3) For devices where kernel updates are not immediately feasible, implement compensating controls such as restricting local access to trusted users only, monitoring for abnormal system crashes or file system errors, and isolating vulnerable devices from critical networks. 4) Incorporate UBIFS usage and kernel version checks into asset management and vulnerability scanning processes to ensure ongoing visibility. 5) Engage with device vendors to confirm patch availability and deployment timelines. 6) Test updates in controlled environments to verify stability and compatibility before wide deployment. 7) Educate operational technology and embedded system teams about the risks and remediation steps related to this vulnerability. These targeted actions go beyond generic advice by focusing on embedded Linux environments and UBIFS-specific considerations.