CVE-2020-36779 is a vulnerability identified in the Linux kernel specifically affecting the I2C driver for the STM32F7 series microcontrollers. The issue arises from improper handling of the power management (PM) reference count in the stm32f7_i2c_xx functions. The vulnerability is due to the use of the function pm_runtime_get_sync, which increments the PM reference count even when it fails. This behavior leads to a reference leak because the code does not properly decrement or balance the usage counter upon failure. The consequence is that the PM reference count becomes inconsistent, potentially causing resource leaks or improper power management states. The fix involves replacing pm_runtime_get_sync with pm_runtime_resume_and_get, which ensures the usage counter remains balanced by only incrementing the reference count when appropriate. This vulnerability is subtle and relates to kernel power management internals, affecting systems running Linux kernels with the affected STM32F7 I2C driver code. There are no known exploits in the wild, and no CVSS score has been assigned yet. The vulnerability does not appear to allow direct code execution or privilege escalation but may lead to resource exhaustion or system instability due to improper power management reference counting.

For European organizations, the impact of CVE-2020-36779 is primarily relevant to embedded systems or devices using STM32F7 microcontrollers running Linux kernels with the affected driver. Such devices might be found in industrial control systems, IoT deployments, or specialized hardware used in sectors like manufacturing, automotive, or telecommunications. The improper reference counting could lead to resource leaks, causing degraded device performance, unexpected power states, or system instability. While this may not directly compromise confidentiality or integrity, availability could be affected if devices enter erroneous power states or crash due to resource exhaustion. In critical infrastructure or industrial environments, such disruptions could have operational consequences. However, the lack of known exploits and the technical nature of the vulnerability suggest that widespread impact is limited unless combined with other vulnerabilities or exploited in targeted attacks.

To mitigate CVE-2020-36779, organizations should ensure that their Linux kernel versions include the patch replacing pm_runtime_get_sync with pm_runtime_resume_and_get in the stm32f7_i2c_xx driver functions. This requires updating to the latest stable Linux kernel releases or applying vendor-provided patches for embedded devices using STM32F7 microcontrollers. Additionally, organizations should audit their embedded Linux devices to identify those running affected kernel versions and plan firmware or kernel updates accordingly. Monitoring device logs for unusual power management errors or resource leaks can help detect potential exploitation attempts or instability. For critical systems, implementing redundancy and failover mechanisms can reduce the impact of device failures. Finally, maintaining strict control over device firmware updates and ensuring secure update mechanisms will prevent attackers from exploiting this or related vulnerabilities.