CVE-2024-36899 is a use-after-free vulnerability identified in the Linux kernel's GPIO (General Purpose Input/Output) subsystem, specifically within the character device interface (cdev) handling code. The flaw arises during the release process of a GPIO chip device file, where the watched_lines bitmap is freed prematurely before the unregistration of the lineinfo_changed_nb notifier chain completes. The root cause is a race condition involving the read-write semaphore (rwsem) used to synchronize access to the notifier chain. When gpio_chrdev_release() is called to close the device file, bitmap_free() is invoked to free watched_lines, but the unregistration of the notifier chain blocks due to contention on the write lock of the rwsem. Meanwhile, another GPIO line release process holds the read lock of the same rwsem and attempts to access watched_lines, resulting in a use-after-free scenario. This leads to a situation where a GPIO line event is erroneously generated for userspace, although the device file is already closed, preventing userspace from reading the event. The vulnerability is fixed by deferring the bitmap_free() call until after the notifier chain unregistration completes, ensuring proper synchronization and preventing the use-after-free condition. The issue affects specific Linux kernel versions identified by commit hashes and was published on May 30, 2024. There are no known exploits in the wild at this time, and no CVSS score has been assigned yet.

For European organizations, the impact of CVE-2024-36899 is primarily related to system stability and potential denial of service in environments relying on Linux-based embedded systems or servers that utilize GPIO interfaces extensively, such as industrial control systems, IoT devices, and specialized hardware platforms. Although the vulnerability does not directly expose sensitive data or allow privilege escalation, the use-after-free condition could lead to kernel crashes or unpredictable behavior in affected systems, potentially disrupting critical operations. This is particularly relevant for sectors like manufacturing, energy, transportation, and telecommunications, where Linux-based embedded devices are common. The inability for userspace to read the spurious GPIO events somewhat limits the exploitation scope, but the underlying race condition could be leveraged in complex attack chains or combined with other vulnerabilities to escalate impact. Organizations running custom or older Linux kernels with the affected GPIO character device code should be vigilant. The absence of known exploits reduces immediate risk, but the vulnerability's presence in the kernel code base necessitates prompt patching to maintain system integrity and availability.

European organizations should prioritize updating their Linux kernel to the latest patched versions that include the fix for CVE-2024-36899. Specifically, kernel maintainers and system integrators should ensure that the bitmap_free() call is deferred until after the notifier chain unregistration completes, as per the official patch. For embedded and IoT devices where kernel updates may be slower, applying backported patches or vendor-provided security updates is critical. Additionally, organizations should audit their use of GPIO interfaces and device drivers to identify systems potentially affected by this vulnerability. Implementing kernel lockdown features and restricting access to GPIO device files can reduce the attack surface. Monitoring kernel logs for abnormal GPIO events or device file closures may help detect attempts to trigger the race condition. Finally, incorporating this vulnerability into vulnerability management and patching workflows will ensure timely remediation and reduce exposure.