CVE-2021-47395 is a vulnerability identified in the Linux kernel's mac80211 subsystem, specifically within the ieee80211_parse_tx_radiotap routine. This vulnerability arises due to insufficient validation of the Very High Throughput (VHT) Modulation and Coding Scheme (MCS) and Number of Spatial Streams (NSS) values injected via radiotap headers. Radiotap headers are used for injecting additional metadata into 802.11 frames, often utilized in wireless packet injection and monitoring tools. The vulnerability was discovered following warnings generated by the syzbot fuzzing infrastructure, which highlighted improper handling of out-of-range or malformed VHT MCS/NSS values. The root cause is that the ieee80211_parse_tx_radiotap function did not adequately limit the maximum values for these parameters, potentially leading to undefined behavior or kernel warnings. The vulnerability is located in the mac80211 wireless networking stack, which is responsible for managing Wi-Fi protocol operations in the Linux kernel. The detailed kernel trace shows the issue occurs during the processing of injected frames, which could be exploited by an attacker capable of injecting crafted radiotap frames to trigger the flaw. While the vulnerability does not appear to have a known exploit in the wild, it could be leveraged for denial of service (DoS) attacks by causing kernel warnings or crashes, potentially impacting system stability. The vulnerability affects Linux kernel version 5.14.0-syzkaller and likely other versions with similar mac80211 implementations. The fix involves limiting the maximum allowed values for VHT MCS and NSS in the parsing routine to prevent out-of-bound accesses or invalid state transitions. No CVSS score is provided, but the vulnerability is primarily a robustness issue in the wireless stack that could be triggered by local or network-based attackers with the ability to inject frames. It does not appear to allow privilege escalation or remote code execution directly but may cause system instability or denial of service.

For European organizations, the impact of CVE-2021-47395 depends largely on their use of Linux-based systems with wireless networking capabilities, particularly those utilizing the mac80211 stack for Wi-Fi communications. Organizations operating wireless infrastructure, embedded devices, or IoT systems running vulnerable Linux kernels could face risks of service disruption due to kernel warnings or crashes triggered by crafted wireless frames. This could lead to denial of service conditions affecting network availability, potentially disrupting business operations reliant on wireless connectivity. Critical infrastructure sectors such as telecommunications, manufacturing, and transportation that deploy Linux-based wireless devices may be particularly sensitive to such disruptions. However, since exploitation requires the ability to inject malicious radiotap frames, the attack surface is somewhat limited to environments where attackers can transmit crafted Wi-Fi frames within radio range. The vulnerability does not appear to allow unauthorized access or data compromise directly but could be used as part of a broader attack chain to degrade system reliability or availability. Given the widespread use of Linux in European enterprise and public sector environments, especially in network infrastructure and embedded systems, the vulnerability warrants timely remediation to maintain operational stability and security.

1. Apply Kernel Updates: Organizations should promptly update Linux kernels to versions where this vulnerability is patched. Monitoring vendor advisories and applying security patches is critical. 2. Wireless Network Segmentation: Limit exposure of vulnerable wireless devices by segmenting wireless networks and restricting access to trusted users and devices only. 3. Frame Injection Controls: Deploy wireless intrusion detection/prevention systems (WIDS/WIPS) capable of detecting and blocking malformed or suspicious radiotap frames to reduce the risk of exploitation. 4. Harden Wireless Interfaces: Disable unnecessary wireless interfaces or features that allow frame injection if not required for business operations. 5. Monitor System Logs: Implement monitoring of kernel logs for warnings or errors related to ieee80211 or mac80211 subsystems to detect potential exploitation attempts early. 6. Incident Response Preparedness: Prepare response plans for potential denial of service incidents affecting wireless infrastructure, including fallback connectivity options. 7. Vendor Coordination: For embedded or IoT devices using Linux kernels, coordinate with vendors to ensure timely firmware updates addressing this vulnerability. These measures go beyond generic advice by focusing on controlling the attack vector (frame injection), monitoring for exploitation signs, and ensuring patch management in wireless environments.