CVE-2021-47385 is a vulnerability identified in the Linux kernel's hardware monitoring (hwmon) subsystem, specifically within the w83792d driver. The issue arises from a NULL pointer dereference caused by improper handling of a structure field related to device value reads. The vulnerability occurs when the driver reads a value 'val' from the device that satisfies the condition (val & 0x08) && (!(val & 0x80)) && ((val & 0x7) == ((val >> 4) & 0x7)). This condition can be met if the temporary variable 'tmp' has a bit pattern of the form 0b0xyz1xyz, where the same literals represent identical numbers. Under these circumstances, a NULL pointer dereference can occur, potentially leading to a kernel crash or system instability. The root cause was linked to the presence of an unnecessary structure field 'lm75[]', which became obsolete after switching to the devm_i2c_new_dummy_device() function in the w83791d_detect_subclients() routine. The patch addressing this vulnerability removes the redundant 'lm75[]' field, thereby preventing the NULL pointer dereference. This vulnerability was discovered by the Linux Driver Verification project (linuxtesting.org) and has been publicly disclosed without any known exploits in the wild. The affected versions correspond to specific Linux kernel commits identified by the hash 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2. No CVSS score has been assigned to this vulnerability as of the publication date (May 21, 2024).

For European organizations, the impact of CVE-2021-47385 primarily involves potential denial of service (DoS) conditions due to kernel crashes triggered by the NULL pointer dereference in the Linux kernel's hwmon subsystem. Systems running affected Linux kernel versions with the w83792d driver enabled could experience unexpected reboots or instability, which may disrupt critical services, especially in environments relying on hardware monitoring for system health and performance. While this vulnerability does not appear to allow privilege escalation or remote code execution, the resulting system crashes could impact availability and operational continuity. Organizations with infrastructure that includes embedded Linux devices, industrial control systems, or servers using affected kernel versions may be particularly vulnerable. Given the absence of known exploits, the immediate threat level is moderate; however, the potential for future exploit development exists, especially if attackers find ways to trigger the condition remotely or via user interaction. The impact on confidentiality and integrity is minimal, but availability could be significantly affected in sensitive environments.

To mitigate CVE-2021-47385, European organizations should prioritize updating their Linux kernel to a version that includes the patch removing the unnecessary 'lm75[]' structure field and fixing the NULL pointer dereference in the w83792d driver. Specifically, applying the latest stable kernel releases or vendor-provided security updates that address this vulnerability is essential. For environments where immediate patching is not feasible, organizations should audit their systems to identify the presence of the w83792d driver and assess whether it is actively used. If the driver is not required, disabling or blacklisting it can reduce exposure. Additionally, implementing robust monitoring to detect kernel crashes or abnormal system behavior can help identify exploitation attempts. For embedded or specialized devices, coordinate with hardware vendors to obtain firmware or kernel updates. Finally, maintaining strict access controls and limiting user privileges can reduce the risk of triggering the vulnerability through untrusted inputs.