CVE-2021-47384 is a medium-severity vulnerability identified in the Linux kernel's hardware monitoring (hwmon) subsystem, specifically within the w83793 driver. The issue arises from a NULL pointer dereference caused by an unnecessary structure field (lm75[]) that was retained after switching to a new dummy device creation method (devm_i2c_new_dummy_device()) in the w83791d_detect_subclients() function. The vulnerability manifests when the driver reads a temperature (tmp) value from the device that satisfies the condition (tmp & 0x08) && (!(tmp & 0x80)) && ((tmp & 0x7) == ((tmp >> 4) & 0x7)), which can occur if tmp matches a specific bit pattern (0b0xyz1xyz). Under these conditions, the driver dereferences a NULL pointer, leading to a kernel crash (denial of service). The flaw was discovered by the Linux Driver Verification project and fixed by removing the redundant lm75[] structure field, thereby preventing the NULL pointer dereference. The vulnerability does not impact confidentiality or integrity but affects availability due to potential kernel panics. Exploitation requires no privileges or user interaction and can be triggered remotely if the vulnerable driver is accessible. However, no known exploits are currently reported in the wild. The CVSS v3.1 base score is 5.3 (medium), reflecting the ease of exploitation and limited impact scope.

For European organizations, the primary impact of CVE-2021-47384 is the potential for denial of service on Linux systems utilizing the affected hwmon w83793 driver. This could lead to system instability or crashes, disrupting critical services, especially in environments relying on Linux for servers, embedded systems, or industrial control where hardware monitoring is essential. While the vulnerability does not compromise data confidentiality or integrity, availability interruptions could affect operational continuity, particularly in sectors such as manufacturing, telecommunications, and data centers. Organizations running Linux kernels with this driver enabled should be aware that remote exploitation is possible without authentication, increasing risk in exposed network environments. However, the absence of known exploits reduces immediate threat levels. Still, unpatched systems remain vulnerable to potential future attacks targeting this flaw.

1. Apply the official Linux kernel patch that removes the unnecessary lm75[] structure field and fixes the NULL pointer dereference in the w83793 driver. 2. Update Linux kernel versions to those including the fix for CVE-2021-47384 as soon as possible, prioritizing production and critical systems. 3. Audit systems to identify usage of the w83793 hwmon driver and assess exposure, especially on network-facing devices. 4. Where immediate patching is not feasible, consider disabling the w83793 driver if hardware monitoring is not critical or use kernel boot parameters to blacklist the module temporarily. 5. Implement monitoring for kernel crashes and system reboots that may indicate exploitation attempts. 6. Restrict network access to devices running vulnerable kernels to trusted networks only, minimizing remote attack surface. 7. Incorporate this vulnerability into vulnerability management and incident response plans to ensure timely detection and remediation.