Linux Kernel EUVD-2026-26522

FUSE (Filesystem in Userspace) is a Linux kernel subsystem that exposes a device interface allowing unprivileged userspace programs to implement fully functional filesystems. The synchronous init path - used when the mounting thread itself handles FUSE_INIT before the mount completes - keeps the FUSE device fd open during the init handshake. This creates a recursive fd-hold: the mounting thread is the sole holder of the device, so if the userspace FUSE server exits abnormally (crash, SIGKILL, etc.) during FUSE_INIT processing, the kernel's abort logic cannot fire because it depends on all holders of the fd closing it first. The async mount path does not exhibit this because the mount syscall completes before FUSE_INIT is processed, meaning no recursive open is active. The root cause is a signal-handling gap in the synchronous init flow - the kernel does not check for fatal pending signals to break the wait loop when the fd owner is the waiter itself. CPE cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* covers all affected kernel versions; NVD did not assign a CWE, but the class is best described as improper handling of exceptional conditions (CWE-755) or a resource locking / signal-response failure.