CVE-2021-47006 is a medium-severity vulnerability affecting the Linux kernel, specifically related to the ARM architecture's hardware breakpoint (hw_breakpoint) subsystem. The issue stems from a logic flaw introduced by commit 1879445dfa7b, which set a default overflow_handler for performance events in the perf_event_alloc() function. This change replaced a direct check of the event's overflow_handler pointer with a check using is_default_overflow_handler(), but missed one critical check. Consequently, the bp->overflow_handler pointer can never be NULL, causing the enable_single_step() function to never be invoked as intended. This flaw impacts the handling of hardware breakpoints and single-step debugging events, potentially leading to improper event overflow handling. The vulnerability does not affect confidentiality or integrity but can cause availability issues by disrupting normal kernel operations related to performance monitoring and debugging. The CVSS 3.1 score is 5.5 (medium), reflecting a local attack vector (AV:L), low attack complexity (AC:L), requiring low privileges (PR:L), no user interaction (UI:N), unchanged scope (S:U), and no impact on confidentiality or integrity but high impact on availability (A:H). There are no known exploits in the wild, and no patches or exploit code links are provided in the source information. The vulnerability is specific to Linux kernel versions containing the referenced commit and affects ARM-based systems using the perf subsystem for hardware breakpoints.

For European organizations, the impact of CVE-2021-47006 is primarily on systems running Linux kernels with the affected commit on ARM architectures. This includes servers, embedded devices, and IoT infrastructure that rely on Linux ARM kernels for performance monitoring and debugging. The vulnerability can cause denial of service or system instability by preventing proper handling of hardware breakpoint overflow events, potentially disrupting critical monitoring or debugging tasks. Organizations using ARM-based Linux servers or network equipment could experience degraded system reliability or availability, impacting operational continuity. However, since the vulnerability does not compromise confidentiality or integrity, the risk of data breaches or unauthorized access is low. The medium severity suggests that while the threat is not critical, it should be addressed promptly to avoid availability issues, especially in environments where performance monitoring is essential for security or compliance. European sectors with high ARM Linux deployment, such as telecommunications, automotive, and industrial control systems, may be more affected.

To mitigate CVE-2021-47006, European organizations should: 1) Identify and inventory all Linux systems running ARM architectures, particularly those using kernel versions containing the affected commit (1879445dfa7b). 2) Apply the latest Linux kernel patches or updates from trusted sources that address this vulnerability as soon as they become available. 3) For systems where immediate patching is not feasible, consider disabling or limiting the use of the perf subsystem or hardware breakpoint features to reduce exposure. 4) Monitor system logs and performance monitoring tools for anomalies or failures related to hardware breakpoint events. 5) Engage with Linux distribution vendors and ARM hardware providers to obtain timely security updates and guidance. 6) Implement robust change management and testing procedures to validate kernel updates before deployment in production environments. 7) Where applicable, isolate critical ARM Linux systems from untrusted networks to reduce the risk of local exploitation.