CVE-2024-56683 is a vulnerability identified in the Linux kernel's Direct Rendering Manager (DRM) subsystem, specifically within the vc4 driver that handles HDMI output on certain hardware platforms. The issue arises when the system attempts to read debug registers located at /sys/kernel/debug/dri/1/hdmi1_regs while the HDMI connection is physically disconnected. This action leads to a fatal system hang due to the interaction with the power management (pm) suspend code. The root cause is that the pm suspend code disables the DVP clock, which is a gate controlling the 108MHz clock in the DVP_HT_RPI_MISC_CONFIG register. Disabling this clock results in accesses hanging on the AXI bus, a critical interconnect for data transfer between components. Consequently, any attempt to access these debug registers under these conditions causes the system to become unresponsive. The vulnerability has been addressed by implementing protections to prevent such hangs during suspend states when HDMI is disconnected. The affected versions include several Linux kernel commits identified by their hashes, indicating that this issue is present in recent kernel builds prior to the patch. There are no known exploits in the wild at this time, and no CVSS score has been assigned yet. This vulnerability is primarily a denial-of-service (DoS) condition triggered by specific hardware and software states involving HDMI disconnection and system suspend operations.

For European organizations, the impact of CVE-2024-56683 is primarily related to system availability and stability. Systems running affected Linux kernel versions on hardware platforms using the vc4 driver for HDMI output—commonly found in embedded devices, IoT gateways, and certain ARM-based systems—may experience fatal hangs if the vulnerability is triggered. This could disrupt critical services, especially in environments where Linux-based devices are used for digital signage, industrial control, or network infrastructure that relies on HDMI output and suspend/resume cycles. While the vulnerability does not appear to allow privilege escalation or data compromise, the denial-of-service effect could lead to operational downtime, impacting business continuity and potentially causing financial losses. The absence of known exploits reduces immediate risk, but organizations should remain vigilant. The impact is more pronounced in sectors with high dependence on embedded Linux devices, such as manufacturing, telecommunications, and public infrastructure, which are prevalent across Europe.

To mitigate CVE-2024-56683, organizations should: 1) Apply the latest Linux kernel patches that address this vulnerability as soon as they become available, ensuring that the vc4 driver and related DRM components are updated. 2) Audit and monitor systems using the affected hardware platforms to identify devices running vulnerable kernel versions. 3) Implement operational controls to avoid scenarios where the system attempts to read HDMI debug registers while the HDMI connection is disconnected, particularly during suspend/resume cycles. This may include scripting or configuration changes to disable such debug reads or to manage HDMI connections more robustly. 4) For embedded and IoT devices, consider firmware updates or vendor-provided patches that incorporate the kernel fix. 5) Establish monitoring for system hangs or crashes related to HDMI operations to detect potential exploitation attempts or inadvertent triggers. 6) Engage with hardware and software vendors to confirm the presence of patches and coordinate updates. These steps go beyond generic advice by focusing on the specific interaction between HDMI state, debug register access, and suspend behavior that triggers the vulnerability.