CVE-2021-47534 is a vulnerability identified in the Linux kernel's Direct Rendering Manager (DRM) subsystem, specifically within the vc4 driver responsible for managing the VideoCore IV GPU used in some Broadcom SoCs. The issue stems from a missing reference decrement operation (drm_crtc_commit_put) in the commit synchronization logic introduced by commit 9ec03d7f1ed3. This commit added a global state for the Hardware Video Scaler (HVS) and implemented synchronization of FIFO queues by tracking the current CRTC (Cathode Ray Tube Controller) commit. However, the refcounting mechanism was flawed, causing a memory leak of the drm_crtc_commit structure on every commit operation. Although this vulnerability does not directly impact confidentiality or integrity, it affects availability by leaking kernel memory resources, which over time could lead to resource exhaustion and potential denial of service (DoS). The CVSS 3.1 score of 4.1 reflects a medium severity, with the attack vector being local (AV:L), requiring high complexity (AC:H), high privileges (PR:H), no user interaction (UI:N), and impacting availability only (A:H). There are no known exploits in the wild, and the vulnerability requires authenticated local access with elevated privileges, limiting its exploitation scope. The flaw is fixed by adding the missing drm_crtc_commit_put call to properly decrement the reference count and prevent the memory leak.

For European organizations, the primary impact of CVE-2021-47534 is the potential for denial of service on systems running affected Linux kernel versions with the vc4 DRM driver enabled. This is particularly relevant for organizations using embedded Linux devices or servers that utilize Broadcom VideoCore IV GPUs, such as certain Raspberry Pi models or other ARM-based platforms common in industrial, IoT, or edge computing environments. While the vulnerability does not allow unauthorized data access or code execution, persistent memory leaks can degrade system stability and availability, potentially interrupting critical services or operations. Organizations relying on Linux-based infrastructure for media processing, digital signage, or specialized hardware acceleration may experience increased maintenance overhead or unexpected downtime if the vulnerability is exploited or triggered by faulty software. Given the requirement for local high-privilege access, the threat is more significant in environments where multiple users have elevated privileges or where attackers have already gained partial access to systems.

To mitigate CVE-2021-47534, European organizations should ensure that their Linux kernel versions are updated to include the patch that adds the missing drm_crtc_commit_put call. This involves applying the latest stable kernel updates from trusted Linux distributions or compiling the kernel with the fix if using custom builds. Organizations should audit systems running the vc4 DRM driver to identify affected devices, especially embedded or ARM-based platforms. Restricting local access to trusted users and enforcing the principle of least privilege can reduce the risk of exploitation, as the vulnerability requires high privileges. Additionally, monitoring system logs and kernel memory usage can help detect abnormal resource consumption indicative of memory leaks. For critical systems, implementing automated patch management and testing procedures will ensure timely deployment of fixes. Finally, organizations should consider isolating or segmenting devices with the affected hardware to limit potential impact.