CVE-2021-47618 is a vulnerability identified in the Linux kernel specifically affecting ARM 32-bit architectures when both Kernel Address Sanitizer (KASAN) and kprobe debugging features are enabled simultaneously. The issue arises because arm32 uses software simulation to replace instructions intercepted by kprobe, which involves constructing assembly functions and binding registers in C to simulate instruction execution. When KASAN is enabled, it alters the register binding relationships, causing the instruction simulation to malfunction. This leads to errors during the simulation of instructions such as 'ldr' (load register), resulting in kernel panics due to NULL pointer dereferences. The vulnerability manifests as a kernel panic triggered by the failure in the emulate_ldr function, which attempts to simulate the 'ldr' instruction but encounters corrupted register states caused by KASAN's interference. The kernel panic logs show an inability to handle a NULL pointer dereference at a specific virtual address, with the panic occurring during the execution of cap_capable, a kernel function related to capability checks. The root cause is that KASAN's instrumentation disrupts the register bindings required for correct instruction simulation by kprobe, leading to invalid memory accesses and system crashes. The fix involves disabling KASAN when compiling the kprobe emulate instruction functions (actions-common.c, actions-arm.c, actions-thumb.c) to prevent the register binding destruction and subsequent kernel panic. This vulnerability is specific to ARM 32-bit Linux kernels with both KASAN and kprobe enabled, and it does not affect other architectures or configurations without these features enabled together. No known exploits are reported in the wild, and no CVSS score has been assigned yet.

For European organizations, the impact of CVE-2021-47618 primarily concerns systems running ARM 32-bit Linux kernels with both KASAN and kprobe enabled. Such configurations are typically found in development, debugging, or specialized embedded environments rather than general production servers. However, organizations involved in embedded systems, IoT devices, or ARM-based development platforms could experience system instability or denial of service due to kernel panics triggered by this vulnerability. The kernel panic results in abrupt system crashes, potentially causing service interruptions, data loss, and operational downtime. In critical infrastructure or industrial control systems using ARM 32-bit Linux kernels, this could lead to significant disruptions. Since the vulnerability requires specific kernel features enabled simultaneously, the attack surface is limited, but the inability to handle kernel panics gracefully can affect system reliability and availability. European organizations relying on ARM-based Linux devices for edge computing, telecommunications, or industrial applications should be aware of this issue. The absence of known exploits reduces immediate risk, but unpatched systems remain vulnerable to accidental or intentional triggering of kernel panics, impacting system stability and availability.

To mitigate CVE-2021-47618, European organizations should: 1) Audit their ARM 32-bit Linux kernel deployments to identify systems with both KASAN and kprobe enabled, focusing on development and embedded environments. 2) Apply the official Linux kernel patches that disable KASAN when compiling the kprobe emulate instruction functions (actions-common.c, actions-arm.c, actions-thumb.c) to prevent register binding corruption. 3) If patching is not immediately feasible, consider disabling either KASAN or kprobe on affected systems to avoid the conflicting interaction causing kernel panics. 4) Implement robust monitoring and alerting for kernel panics and system crashes on ARM 32-bit devices to detect potential exploitation or accidental triggers promptly. 5) For embedded and IoT devices, coordinate with vendors to ensure firmware updates include the fix or disable conflicting features. 6) Conduct thorough testing of kernel updates in staging environments to verify stability before deployment in production. 7) Educate development and operations teams about the risk of enabling both KASAN and kprobe simultaneously on ARM 32-bit kernels to prevent misconfiguration. These targeted actions go beyond generic advice by focusing on the specific kernel features and compilation settings involved in this vulnerability.