CVE-2021-47388 is a use-after-free vulnerability found in the Linux kernel's mac80211 subsystem, which is responsible for handling Wi-Fi (802.11) protocol operations. Specifically, the flaw occurs during the processing of CCMP/GCMP encrypted frames in the receive (RX) path. The vulnerability arises from improper handling of the Packet Number (PN) checking mechanism during frame defragmentation. In the affected code, after a commit (bf30ca922a0c) introduced PN comparison against the current frame, the 'hdr' variable—representing the frame header—was used without ensuring its validity post potential frame reallocations. This led to a use-after-free condition when the frame needed to be reallocated during defragmentation, causing the 'hdr' pointer to reference freed memory. Exploiting this flaw could allow an attacker to cause memory corruption, potentially leading to kernel crashes (denial of service) or, in more severe cases, arbitrary code execution with kernel privileges. The vulnerability affects multiple Linux kernel versions identified by specific commits, indicating it has been present for some time before being patched. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet. The fix involves reloading the 'hdr' variable after any code that may cause frame reallocations, ensuring the pointer remains valid before use.

For European organizations, this vulnerability poses a significant risk primarily to systems running vulnerable Linux kernel versions with Wi-Fi capabilities relying on the mac80211 stack. This includes servers, desktops, embedded devices, and IoT devices using Linux-based Wi-Fi drivers. Exploitation could lead to denial of service through kernel crashes, disrupting critical services and operations. More critically, if exploited for arbitrary code execution, attackers could gain kernel-level privileges, compromising system confidentiality, integrity, and availability. This could facilitate lateral movement within networks, data exfiltration, or persistent backdoors. Given the widespread use of Linux in enterprise environments, telecommunications infrastructure, and critical systems across Europe, the vulnerability could impact sectors such as finance, healthcare, government, and industrial control systems. The lack of known exploits currently reduces immediate risk, but the presence of a use-after-free in kernel Wi-Fi processing is a high-value target for attackers, especially in targeted attacks or espionage campaigns.

European organizations should prioritize updating their Linux kernels to versions where this vulnerability is patched. Since the issue is in the mac80211 subsystem, kernel updates from trusted vendors or distributions that include the fix should be applied promptly. For embedded and IoT devices, coordinate with device manufacturers to obtain firmware updates or consider network segmentation to isolate vulnerable devices. Additionally, implement strict network access controls to limit exposure of Wi-Fi-enabled devices to untrusted networks. Monitoring kernel logs for unusual crashes or anomalies in Wi-Fi traffic can help detect exploitation attempts. Employing host-based intrusion detection systems (HIDS) with kernel integrity monitoring can also aid in early detection. For environments where immediate patching is not feasible, disabling Wi-Fi or restricting wireless interfaces temporarily can reduce attack surface. Finally, maintain an inventory of Linux-based devices and their kernel versions to ensure comprehensive coverage of patching efforts.