CVE-2021-47091 is a vulnerability identified in the Linux kernel, specifically within the mac80211 subsystem, which handles wireless networking functionality. The issue pertains to improper locking in the ieee80211_start_ap error path. The vulnerability arises because the local->mtx mutex lock is not held when releasing the channel context during error handling, despite the presence of a lockdep_assert_held() assertion indicating that the lock should be held. This improper locking can lead to race conditions or inconsistent state management within the wireless access point start procedure. The flaw was addressed by ensuring that the local->mtx mutex is properly acquired before releasing the channel context, thereby maintaining synchronization and preventing potential kernel instability or unexpected behavior. Although the vulnerability does not have any known exploits in the wild as of now, it affects the Linux kernel versions identified by the commit hash 295b02c4be74bebf988593b8322369513fcecf68. Since mac80211 is a core component for wireless networking on Linux systems, this vulnerability could impact any Linux-based device or server that uses wireless access point functionality. The vulnerability is technical and low-level, related to kernel locking mechanisms, which are critical for system stability and security. Improper locking can potentially be exploited to cause denial of service (system crashes) or, in rare cases, privilege escalation if the race condition can be leveraged by an attacker. However, no direct exploit or privilege escalation has been reported to date.

For European organizations, the impact of CVE-2021-47091 primarily concerns systems running Linux kernels with wireless access point capabilities, such as enterprise wireless routers, IoT devices, embedded systems, and servers providing wireless networking. If exploited, the vulnerability could cause kernel crashes or instability, leading to denial of service conditions on critical network infrastructure. This could disrupt business operations, especially in sectors relying heavily on wireless connectivity such as telecommunications, manufacturing, healthcare, and public services. While there is no evidence of active exploitation, the potential for disruption exists, particularly in environments where wireless access points are managed via Linux-based systems. Confidentiality and integrity impacts are less likely unless combined with other vulnerabilities, but availability could be significantly affected. Additionally, organizations with large-scale wireless deployments may face operational challenges if the vulnerability is triggered unintentionally or through malformed wireless management frames. Given the kernel-level nature of the flaw, recovery from crashes may require system reboots, causing downtime. The lack of known exploits reduces immediate risk, but the presence of the vulnerability in widely used Linux kernels necessitates proactive mitigation to avoid future exploitation.

To mitigate CVE-2021-47091, European organizations should: 1) Apply the latest Linux kernel updates and patches that address this vulnerability as soon as they become available from trusted Linux distributions or vendors. 2) Audit and inventory all Linux-based devices that provide wireless access point functionality to ensure they are running patched kernel versions. 3) Implement strict network segmentation and access controls to limit exposure of wireless access points to untrusted networks or users, reducing the attack surface. 4) Monitor system logs and kernel messages for signs of instability or crashes related to wireless networking components. 5) Employ kernel lockdown or security modules (e.g., SELinux, AppArmor) to restrict unauthorized kernel modifications or exploit attempts. 6) For embedded or IoT devices with limited patching capabilities, consider network-level protections such as firewall rules and intrusion detection systems focused on wireless management traffic. 7) Engage with vendors of Linux-based wireless infrastructure to confirm patch availability and deployment timelines. These steps go beyond generic advice by emphasizing inventory management, network segmentation, and vendor coordination specific to wireless AP Linux kernel components.