CVE-2020-36787 is a vulnerability identified in the Linux kernel specifically affecting the media subsystem for Aspeed AST2500 and AST2600 System on Chips (SoCs). The issue arises from improper clock and reset handling logic in the video engine hardware driver. The video engine relies on two clock sources, eclk and vclk, with reset control coupled to eclk. The flawed sequence enables eclk, de-asserts the video engine reset, waits 10ms, then enables vclk. This sequence can cause improper reset behavior, leading the video engine hardware to generate unexpected Direct Memory Access (DMA) transfers. These sporadic and random DMA operations can corrupt memory regions unpredictably, causing critical kernel panics with varying signatures, making debugging extremely difficult. Notably, this issue can occur even when the video engine is not actively used, as the udev daemon briefly activates the video engine during system boot to query hardware. The fix involves changing the clock handling logic to de-assert the reset only after both eclk and vclk are enabled, and adding proper cleanup calls (clk_unprepare) if the probe fails. Additionally, the reset settings for eclk and vclk on AST2600 are adjusted to align with previous Aspeed SoCs, ensuring the reset bit controlling the video engine is de-asserted only when eclk is enabled, as per the hardware datasheet. This vulnerability is specific to certain Aspeed SoCs used in embedded systems and server management controllers, and no known exploits in the wild have been reported to date.

For European organizations, the impact of CVE-2020-36787 depends largely on the deployment of affected Aspeed AST2500/AST2600 SoCs within their infrastructure. These SoCs are commonly found in Baseboard Management Controllers (BMCs) used in server management, particularly in data centers and enterprise-grade hardware. A kernel panic caused by this vulnerability can lead to unexpected system crashes, resulting in denial of service conditions. Memory corruption caused by errant DMA transfers could also potentially be leveraged to destabilize systems or cause data integrity issues, although no direct exploitation has been observed. For critical infrastructure operators, cloud service providers, and enterprises relying on Linux-based servers with affected hardware, this vulnerability could disrupt availability and complicate incident response due to the sporadic and hard-to-debug nature of the crashes. While confidentiality and integrity impacts are less clear without active exploitation, the instability and potential for system downtime pose significant operational risks. The fact that the issue can manifest even without active video engine use increases the attack surface, as normal system boot processes can trigger the fault.

European organizations should prioritize updating their Linux kernel versions to incorporate the patch that corrects the clock and reset handling logic for the Aspeed video engine driver. Specifically, ensure that kernel versions include the fix that defers reset de-assertion until both eclk and vclk clocks are enabled and that proper cleanup is performed on probe failures. Organizations should audit their hardware inventory to identify systems using AST2500 or AST2600 SoCs, typically found in BMCs or embedded server management controllers. For affected systems where immediate patching is not feasible, consider isolating or limiting access to management interfaces to reduce risk exposure. Monitoring system logs for unexplained kernel panics or memory corruption signatures related to the video engine may help detect attempts to trigger the vulnerability. Collaborate with hardware vendors to confirm firmware and driver updates are applied. Additionally, implement robust backup and recovery procedures to mitigate potential data loss or downtime caused by unexpected crashes. Since no known exploits exist, proactive patching and hardware inventory management are the most effective defenses.