CVE-2021-47533 is a use-after-free vulnerability found in the Linux kernel's Direct Rendering Manager (DRM) subsystem, specifically within the vc4 driver that handles the VideoCore IV GPU used in some Broadcom SoCs. The issue arises from improper management of the HVS (Hardware Video Scaler) FIFO commit pointer. A recent commit introduced a synchronization mechanism that waits for the completion of a previous FIFO commit before proceeding. However, the pointer to the previous commit was not cleared after the wait completed. Because drm_crtc_commit_put can free the drm_crtc_commit structure if it is the last user, retaining a stale pointer leads to a use-after-free condition when the state is duplicated and the stale pointer is copied to the new state. This can cause memory corruption, potentially leading to kernel crashes or arbitrary code execution in kernel context if exploited. The vulnerability affects Linux kernel versions containing the faulty commit 9ec03d7f1ed3. No public exploits are known at this time, and no CVSS score has been assigned. The fix involves setting the pointer to NULL after the wait completes to prevent carrying over a pointer to a freed structure.

For European organizations, this vulnerability poses a risk primarily to systems running Linux kernels with the affected vc4 DRM driver, which is common in embedded devices, IoT, and some ARM-based platforms using Broadcom hardware (e.g., Raspberry Pi devices). Exploitation could lead to privilege escalation or denial of service via kernel crashes, impacting availability and integrity of critical systems. Organizations relying on Linux-based infrastructure for industrial control, telecommunications, or edge computing could be affected if they use vulnerable kernel versions. Although no exploits are currently known, the use-after-free nature of the bug means that a successful exploit could allow attackers to execute arbitrary code with kernel privileges, severely compromising confidentiality, integrity, and availability. The impact is more significant in environments where untrusted users or processes have access to the system, as local exploitation is likely required. The vulnerability does not appear to require user interaction but does require the ability to trigger the specific DRM driver code paths.

European organizations should promptly identify Linux systems running affected kernel versions with the vc4 DRM driver enabled, especially embedded and ARM-based devices. Applying the upstream Linux kernel patch that clears the HVS FIFO commit pointer after waiting is the definitive fix. If immediate patching is not feasible, organizations should restrict access to vulnerable systems, limit untrusted user privileges, and monitor for unusual kernel crashes or suspicious activity related to the DRM subsystem. For embedded devices, coordinate with hardware vendors or distributors to obtain updated firmware or kernel images. Additionally, implement kernel hardening techniques such as Kernel Address Space Layout Randomization (KASLR), and enable kernel lockdown features where applicable to reduce exploitation risk. Regularly audit and update Linux kernels to the latest stable releases to minimize exposure to such vulnerabilities.