CVE-2021-47324 is a high-severity use-after-free vulnerability in the Linux kernel's watchdog subsystem, specifically within the wdt_startup() function. The issue arises because the watchdog driver's remove path calls del_timer() to delete a timer, but del_timer() does not wait for the timer handler to complete execution. Consequently, the timer handler may still be running after the driver's remove function has finished, leading to a use-after-free condition where the handler accesses memory that has already been freed. This can cause system instability, crashes, or potentially allow an attacker to execute arbitrary code with kernel privileges. The vulnerability is rooted in improper synchronization between timer deletion and handler execution. The fix involves replacing del_timer() with del_timer_sync(), which ensures that the timer handler has fully completed and cannot reschedule itself before the driver removal completes. This vulnerability affects Linux kernel versions identified by the commit hash 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and likely other versions containing the same code pattern. The CVSS v3.1 score is 8.8, reflecting network attack vector, low attack complexity, requiring privileges but no user interaction, and impacts on confidentiality, integrity, and availability. No known exploits are currently reported in the wild, but the vulnerability's nature and kernel-level impact make it a critical risk if exploited.

For European organizations, this vulnerability poses a significant risk due to the widespread use of Linux in servers, cloud infrastructure, embedded systems, and critical industrial environments. Exploitation could lead to kernel-level code execution, allowing attackers to bypass security controls, escalate privileges, and compromise system integrity and availability. This could disrupt essential services, including financial systems, healthcare infrastructure, telecommunications, and government operations. The use-after-free flaw can cause system crashes or allow attackers to implant persistent malware at the kernel level, complicating detection and remediation. Given the reliance on Linux in data centers and cloud providers across Europe, the vulnerability could affect a broad range of sectors, increasing the risk of data breaches, service outages, and operational disruptions.

European organizations should prioritize patching affected Linux kernel versions by applying updates that replace del_timer() calls with del_timer_sync() in the watchdog driver. Since this is a kernel-level vulnerability, kernel upgrades should be tested and deployed promptly in production environments. Organizations should also audit their systems to identify Linux hosts running vulnerable kernel versions, including embedded devices and IoT systems that may not receive automatic updates. Employing kernel live patching solutions where available can reduce downtime during remediation. Additionally, organizations should implement strict access controls to limit privileged user accounts, as exploitation requires local privileges. Monitoring kernel logs and system behavior for anomalies related to timer operations or unexpected crashes can help detect exploitation attempts. Finally, maintaining robust backup and recovery procedures will mitigate the impact of potential system failures caused by exploitation.