CVE-2022-49174 is a vulnerability in the Linux kernel's ext4 filesystem implementation related to the handling of block bitmaps when the flex_bg feature is enabled (which is the default setting). The ext4_mb_mark_bb() function is responsible for marking blocks in the block bitmap during allocation. However, when an extent spans across blocks from two different block groups, the function only reads the buffer_head of the block bitmap once for the starting block group and fails to update it when the extent crosses into another block group. This leads to out-of-bounds memory access beyond the block group bitmap buffer_head, causing a data abort and kernel crash. The vulnerability manifests as an ext4 filesystem error, inconsistent block bitmap and block group descriptor counts, and ultimately a kernel panic or journal abort. The issue was demonstrated on the Power platform, but it is inherent to the ext4 code path and could affect other architectures using ext4 with flex_bg enabled. The root cause is a missing boundary check and buffer update in ext4_mb_mark_bb(), which was fixed by adding logic to handle block group boundaries correctly and update the buffer_head accordingly. Exploitation does not require user interaction but does require the ability to trigger filesystem operations that allocate extents spanning block groups, such as mounting or writing to ext4 filesystems. No known exploits are reported in the wild, and no CVSS score is assigned yet.

For European organizations, this vulnerability poses a risk of denial of service through kernel crashes or filesystem corruption on Linux systems using ext4 with flex_bg enabled. Since ext4 is the default filesystem for many Linux distributions widely used in Europe, including servers, desktops, and embedded devices, the impact could be significant. A successful exploitation could lead to system instability, data loss, or downtime, affecting critical infrastructure, enterprise servers, cloud environments, and industrial control systems running Linux. The vulnerability could be triggered by local users or processes with filesystem access, potentially including containerized environments or virtual machines using ext4-backed storage. While there is no indication of remote exploitation, the risk to availability and data integrity is notable, especially for organizations relying on ext4 for critical workloads. Recovery from crashes may require filesystem checks and restores, increasing operational overhead and risk of data loss.

European organizations should prioritize updating their Linux kernels to versions that include the patch fixing CVE-2022-49174. Kernel updates from major Linux distributions (e.g., Debian, Ubuntu, Red Hat, SUSE) should be applied promptly. In environments where immediate patching is not feasible, administrators should avoid workloads that cause extents to span multiple block groups, such as large file writes or certain mount operations, although this is a limited workaround. Monitoring kernel logs for ext4 errors or data aborts can help detect attempts to trigger the vulnerability. Additionally, implementing filesystem integrity monitoring and regular backups will mitigate data loss risks. For containerized or virtualized environments, ensure host kernels are patched and consider isolating workloads that heavily use ext4. Finally, organizations should review their incident response plans to handle potential ext4 filesystem corruption or kernel panics.