CVE-2025-21752 is a vulnerability identified in the Linux kernel's Btrfs filesystem implementation, specifically related to the handling of RAID stripe extents within the Btrfs RAID stripe-tree. The vulnerability arises from the improper use of the function btrfs_set_item_key_safe() to modify keys in the RAID stripe-tree. This function is designed to safely update item keys, but when used on RAID stripe extents, it can cause corruption of the tree structure. The corruption is detected by internal consistency checks within btrfs_set_item_key_safe(), which then triggers a kernel BUG, leading to a kernel panic or system crash. The vulnerability manifests as an invalid opcode exception and a kernel oops, indicating a critical failure in kernel execution. The root cause of the corruption is not fully understood, but the recommended safe approach is to use btrfs_duplicate_item() to copy the item and then adjust both the key and the per-device physical addresses, avoiding direct modification via btrfs_set_item_key_safe(). This flaw affects Linux kernel versions prior to the patch and is particularly relevant for systems using Btrfs with RAID configurations. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet.

For European organizations, this vulnerability poses a significant risk to systems running Linux with Btrfs filesystems configured in RAID mode. The impact includes potential data corruption, system instability, and unexpected downtime due to kernel panics triggered by the vulnerability. This can lead to loss of data integrity and availability, especially in environments relying on Btrfs RAID for redundancy and performance. Critical infrastructure, cloud service providers, and enterprises using Linux servers for storage or virtualization could experience service interruptions. The vulnerability could also complicate recovery efforts and increase operational costs due to unplanned outages and data recovery processes. Although exploitation requires triggering specific filesystem operations, the impact on confidentiality is minimal; however, integrity and availability are severely affected. Given the widespread use of Linux in European data centers, research institutions, and government agencies, the vulnerability could have broad operational consequences if unpatched.

To mitigate this vulnerability, European organizations should prioritize updating their Linux kernels to versions where this issue is resolved. Since the root cause involves unsafe modification of RAID stripe-tree keys, administrators should avoid manual or automated processes that directly invoke btrfs_set_item_key_safe() on RAID stripe extents. Instead, ensure that any Btrfs maintenance or repair tools use the recommended safe method involving btrfs_duplicate_item(). System administrators should audit their current Btrfs RAID configurations and monitor kernel logs for signs of corruption or kernel panics related to Btrfs operations. Implementing robust backup and recovery procedures is critical to minimize data loss risks. Additionally, organizations should test kernel updates in staging environments to verify stability before deployment. For environments where immediate patching is not feasible, consider isolating affected systems or limiting workloads that perform intensive Btrfs RAID operations to reduce exposure. Monitoring for unusual filesystem errors or crashes can provide early warning of exploitation attempts or accidental triggers.