CVE-2021-47387 is a vulnerability in the Linux kernel's cpufreq subsystem, specifically within the schedutil governor's handling of the sugov_tunables structure. The issue arises because the sugov_tunables struct is protected by a kobject, and the original code attempted to free this structure directly rather than using the kobject's release() method. This improper memory management leads to a kernel warning and potential instability, as indicated by debug trace logs showing attempts to free an active object incorrectly. The vulnerability manifests as a use-after-free or double-free condition within kernel memory management, which can cause kernel crashes or undefined behavior. The fix involved splitting the original sugov_tunables_free() function into two: sugov_clear_global_tunables(), which clears global tunables, and a new sugov_tunables_free() function used as the kobject release method to safely release the sugov_tunables structure. This correction ensures proper lifecycle management of kernel objects and prevents erroneous freeing of memory. The vulnerability affects Linux kernel versions identified by the commit hash 9bdcb44e391da5c41b98573bf0305a0e0b1c9569 and was published on May 21, 2024. No known exploits are currently reported in the wild, and no CVSS score has been assigned.

For European organizations, the impact of CVE-2021-47387 primarily concerns systems running vulnerable Linux kernel versions with the cpufreq schedutil governor enabled. This includes servers, embedded devices, and potentially critical infrastructure components that rely on Linux for power management and CPU frequency scaling. Exploitation could lead to kernel crashes, causing denial of service (DoS) conditions that disrupt business operations, especially in environments requiring high availability. While the vulnerability does not directly indicate privilege escalation or remote code execution, kernel instability can be leveraged in complex attack chains or cause operational outages. Organizations in sectors such as telecommunications, manufacturing, and cloud services that utilize Linux-based systems could experience service interruptions. Given the kernel-level nature, the vulnerability affects confidentiality, integrity, and availability indirectly through system reliability degradation. The absence of known exploits reduces immediate risk, but unpatched systems remain vulnerable to potential future exploitation or accidental crashes.

To mitigate CVE-2021-47387, European organizations should: 1) Identify all Linux systems running kernel versions associated with the vulnerable commit (9bdcb44e391da5c41b98573bf0305a0e0b1c9569). 2) Apply the official Linux kernel patches that implement the fix by properly using the kobject release() method for sugov_tunables. If official patches are not yet available, consider upgrading to the latest stable kernel versions where this issue is resolved. 3) Disable or avoid using the cpufreq schedutil governor on critical systems if patching is delayed, as a temporary workaround to reduce exposure. 4) Monitor system logs for kernel warnings or crashes related to memory management in the cpufreq subsystem to detect potential exploitation or instability. 5) Implement rigorous kernel update policies and test kernel updates in staging environments before production deployment to minimize downtime. 6) For embedded or specialized devices, coordinate with vendors for firmware or kernel updates addressing this vulnerability. These steps go beyond generic advice by focusing on kernel version tracking, targeted subsystem configuration, and proactive monitoring specific to this vulnerability.