Linux CVE-2026-23432

The vulnerability exists in the Microsoft Hyper-V partition (mshv) driver, a Linux kernel module that provides user-space access to Hyper-V virtualization features. The mshv_map_user_memory() function registers an MMU (Memory Management Unit) notifier to track memory events for a partition region. When an error occurs during memory mapping, the error path calls vfree() directly to free the region structure without invoking mshv_partition_put(), which is responsible for unregistering the MMU notifier. This leaves the notifier registered and pointing to freed memory. Later, when userspace unmaps or modifies the memory, the kernel's MMU notifier subsystem invokes the dangling callback, causing the freed region to be accessed. The root cause is improper resource cleanup in error handling, falling into the CWE category of use-after-free (CWE-416). The fix replaces the direct vfree() call with mshv_partition_put(), ensuring the notifier is properly deregistered before memory is released.