CVE-2022-49699 is a vulnerability identified in the Linux kernel related to the filemap subsystem, specifically within the function filemap_get_read_batch(). The issue arises from a race condition between a read operation and an invalidation followed by another read. In this scenario, a folio (a memory management structure representing a collection of pages) can be replaced with a higher-order folio during the race. This replacement leads to the presence of a sibling entry for the new folio in the subsequent iteration of the loop inside filemap_get_read_batch(). The vulnerability manifests as a NULL pointer dereference while the Read-Copy-Update (RCU) read lock is held, which can cause a kernel crash (denial of service). The root cause is the improper handling of sibling entries during this race condition. The fix involves returning early when this condition is detected, allowing the next call to correctly find and handle the new folio. This approach avoids the complexity of other potential fixes and addresses the rare race condition effectively. The vulnerability affects specific Linux kernel versions identified by the commit hash cbd59c48ae2bcadc4a7599c29cf32fd3f9b78251. There are no known exploits in the wild at the time of publication, and no CVSS score has been assigned yet.

For European organizations, the primary impact of CVE-2022-49699 is the potential for denial of service (DoS) due to kernel crashes triggered by the NULL pointer dereference. This can lead to system instability, unexpected reboots, or downtime, affecting availability of critical services running on Linux-based infrastructure. Given Linux's widespread use in servers, cloud environments, and embedded systems across Europe, this vulnerability could disrupt business operations, especially in sectors relying heavily on Linux for their IT infrastructure such as finance, telecommunications, and government services. Although there is no indication that this vulnerability allows privilege escalation or remote code execution, the resulting DoS could be leveraged as part of a broader attack to degrade service or cause operational disruptions. The absence of known exploits reduces immediate risk, but the vulnerability's presence in the kernel means that any system running affected versions is potentially susceptible to crashes triggered by local or possibly remote processes that perform file read operations under specific race conditions.

European organizations should prioritize updating their Linux kernel to versions where this vulnerability has been patched. Since the fix involves kernel-level changes, applying official kernel updates from trusted Linux distributions is the most effective mitigation. Organizations should: 1) Identify all systems running affected kernel versions using inventory and vulnerability scanning tools. 2) Apply vendor-supplied kernel patches or upgrade to the latest stable kernel releases that include the fix. 3) For systems where immediate patching is not feasible, consider isolating critical systems or limiting access to reduce the risk of triggering the race condition. 4) Monitor system logs for kernel crashes or anomalies related to filemap operations that might indicate attempts to exploit this vulnerability. 5) Engage with Linux distribution vendors for backported patches if using long-term support kernels. 6) Implement robust backup and recovery procedures to minimize downtime in case of crashes. 7) Educate system administrators about the vulnerability and the importance of timely patching to prevent denial of service incidents.