CVE-2021-47386 is a high-severity vulnerability identified in the Linux kernel's hardware monitoring (hwmon) driver for the w83791d chip. The vulnerability arises from a NULL pointer dereference caused by an unnecessary structure field (lm75[]) that was retained after a transition to a new device instantiation method (devm_i2c_new_dummy_device()) in the w83791d_detect_subclients() function. Specifically, if the driver reads a value from the device that satisfies the condition (val & 0x08) && (!(val & 0x80)) && ((val & 0x7) == ((val >> 4) & 0x7)), a NULL pointer dereference can occur. This condition corresponds to certain bit patterns in the device's returned value, which can lead to the driver dereferencing a NULL pointer, causing a kernel crash or system instability. The vulnerability was discovered by the Linux Driver Verification project and has been addressed by removing the obsolete lm75[] structure field, thereby preventing the NULL pointer dereference. The CVSS v3.1 score of 7.8 reflects the vulnerability's high impact on confidentiality, integrity, and availability, requiring low privileges and no user interaction, but local access to the system. This vulnerability affects specific Linux kernel versions identified by their commit hashes. No known exploits are currently reported in the wild.

For European organizations, this vulnerability poses a significant risk primarily to systems running affected Linux kernel versions with the w83791d hardware monitoring driver enabled. The NULL pointer dereference can lead to kernel panics, causing denial of service (DoS) conditions that disrupt critical services and operations. In environments such as data centers, industrial control systems, and embedded devices relying on Linux for hardware monitoring, this could result in system outages and operational downtime. Additionally, the high impact on confidentiality and integrity suggests potential for more severe exploitation if combined with other vulnerabilities, possibly allowing attackers to escalate privileges or execute arbitrary code. Given the widespread use of Linux in European enterprises, government agencies, and infrastructure, the vulnerability could affect a broad range of sectors including finance, manufacturing, telecommunications, and public services. The local access requirement limits remote exploitation but insider threats or compromised local accounts could leverage this flaw to destabilize systems.

European organizations should prioritize patching affected Linux kernel versions by applying the official fixes that remove the unnecessary lm75[] structure field and correct the driver logic in w83791d_detect_subclients(). System administrators must audit their Linux deployments to identify systems using the vulnerable w83791d driver, especially in critical infrastructure and embedded devices. Disabling the hwmon driver for w83791d where hardware monitoring is not essential can serve as a temporary mitigation. Implement strict access controls and monitoring to limit local user privileges and detect anomalous behavior indicative of exploitation attempts. Incorporate kernel crash monitoring and automated recovery mechanisms to minimize downtime. For organizations using custom or older Linux kernels, backporting the patch or upgrading to a supported kernel version is essential. Additionally, integrating this vulnerability into vulnerability management and incident response workflows will ensure timely detection and remediation.