CVE-2021-47113 is a vulnerability identified in the Linux kernel's Btrfs filesystem implementation, specifically within the rename_exchange operation. This operation is designed to atomically swap two filenames, which involves manipulating inode references for both files. The vulnerability arises when the insertion of the second inode reference fails during the rename_exchange process. In such a failure scenario, the first inode reference remains inserted, resulting in a dangling inode reference. This dangling reference can lead to filesystem corruption, as the inode reference count becomes inconsistent, potentially causing data integrity issues or filesystem instability. The root cause is a lack of proper rollback or cleanup when the second insertion fails, which the patch addresses by aborting the operation if the first insertion has already occurred, preventing the filesystem from entering a corrupt state. This vulnerability is not known to be exploited in the wild and affects specific versions of the Linux kernel identified by the commit hash 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2. The issue was discovered through error injection stress testing, highlighting the importance of rigorous testing in uncovering subtle filesystem bugs.

For European organizations, this vulnerability poses a risk primarily to systems running affected Linux kernel versions with Btrfs filesystems. The impact includes potential filesystem corruption, which can lead to data loss, system crashes, or degraded system availability. Organizations relying on Btrfs for critical storage, such as cloud providers, data centers, and enterprises using Linux-based servers, could experience operational disruptions. Although exploitation requires triggering a specific filesystem operation (rename_exchange) and failure conditions, the risk of data integrity compromise is significant in environments where Btrfs is heavily used. This could affect sectors such as finance, healthcare, and government, where data reliability is paramount. Since the vulnerability does not require user interaction or authentication to manifest (it occurs during filesystem operations), any process with sufficient privileges to perform rename_exchange operations could inadvertently trigger the issue. However, the absence of known exploits in the wild reduces immediate threat levels but does not eliminate the risk of future exploitation.

European organizations should prioritize updating their Linux kernels to versions that include the patch for CVE-2021-47113. Specifically, applying the commit identified by the hash 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 or later kernel releases that incorporate this fix is essential. Organizations should audit their systems to identify those using Btrfs filesystems and verify kernel versions. For critical systems where immediate patching is not feasible, implementing filesystem monitoring tools to detect anomalies or corruption signs in Btrfs can provide early warnings. Additionally, maintaining robust backup and recovery procedures is crucial to mitigate potential data loss from filesystem corruption. System administrators should also restrict permissions to limit which processes can perform rename_exchange operations, reducing the attack surface. Finally, incorporating this vulnerability into vulnerability management and incident response plans will ensure preparedness for any exploitation attempts.