CVE-2021-47251 is a vulnerability identified in the Linux kernel's mac80211 subsystem, specifically within the ieee80211_scan_rx() function. The issue arises from the use of hard-coded compile-time constants for header length checks, which are not dynamically adjusted based on the frame type being processed. This flaw can lead to incorrect validation of received 802.11 frames, triggering WARN_ON conditions in the cfg80211 component, which is responsible for wireless configuration. The vulnerability was addressed by replacing these static constants with dynamic calculations that consider the actual frame type, thereby preventing improper length checks and potential kernel warnings or crashes. Although no known exploits are currently reported in the wild, the vulnerability affects Linux kernel versions prior to the patch and could be leveraged to cause denial of service or potentially facilitate further kernel-level attacks if combined with other vulnerabilities. The vulnerability is rooted in the wireless networking stack, which is critical for systems relying on Wi-Fi connectivity. The fix improves the robustness of frame validation and prevents kernel instability caused by malformed or unexpected wireless frames.

For European organizations, this vulnerability poses a risk primarily to systems running vulnerable Linux kernel versions with wireless networking enabled. The impact includes potential denial of service through kernel warnings or crashes triggered by malformed wireless frames, which could disrupt network connectivity and availability of critical services. Organizations with extensive use of Linux-based infrastructure, including servers, workstations, and embedded devices in wireless environments, may experience operational interruptions. Although exploitation requires crafted wireless frames and proximity to the target network, attackers could leverage this vulnerability to degrade service or as a stepping stone for privilege escalation if combined with other kernel exploits. This is particularly relevant for sectors with high reliance on wireless communications such as telecommunications, manufacturing, healthcare, and public administration. The absence of known exploits reduces immediate risk, but the vulnerability's presence in widely deployed Linux kernels necessitates timely remediation to maintain network stability and security.

European organizations should prioritize updating their Linux kernel to the latest patched versions that address CVE-2021-47251. Specifically, kernel updates that replace static header length checks with dynamic frame-type-based validation must be applied promptly. Network administrators should audit their Linux systems to identify vulnerable kernel versions and plan for controlled patch deployment to minimize downtime. Additionally, organizations should monitor wireless network traffic for unusual or malformed 802.11 frames that could indicate attempts to exploit this vulnerability. Implementing network segmentation and restricting wireless access to trusted devices can reduce exposure. For critical infrastructure, consider deploying intrusion detection systems capable of analyzing wireless traffic anomalies. Finally, maintain a robust patch management policy that includes kernel updates and continuous vulnerability scanning to detect and remediate similar issues proactively.