CVE-2026-68095 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
fuse-uring: fix race between registration and connection abortion
This fixes this race: - thread a: io_uring_enter -> register sqe -> fuse_uring_create_ring_ent -> allocate ent but doesn't grab queue_ref yet - thread b: fuse_conn_destroy() -> fuse_chan_abort() -> fuse_uring_abort() is a no-op due to queue ref being 0 - thread a: grabs the queue_ref, queue_ref is now 1, rest of fuse_uring_do_register() logic executes - thread b: fuse_chan_abort() returns, fuse_chan_wait_aborted() now runs and calls "wait_event(ring->stop_waitq, atomic_read(&ring->queue_refs) == 0);" The abort/unmount thread will hang indefinitely in unkillable state as nothing will decrement queue_refs or wake stop_waitq, and the ring, queue, and ent are leaked.
Fix this by checking fch->connected under fch->lock after the created ent has grabbed a ref count on the queue. This ensures that in the scenario above, it is guaranteed that we either release the queue ref and wake up stop_waitq (in case fuse_chan_wait_aborted() is already waiting) in fuse_uring_do_register() when we detect !fch->connected, or if the connection is aborted after the check, it is guaranteed that the async teardown worker will be running in the background cleaning up ents and decrementing the ent's ref on the queue, which will unblock the eventual queue and ring teardown.
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Analysis
by VulDB Data Team • 08/10/2026
This vulnerability exists within the Linux kernel's fuse-uring implementation where a race condition occurs between thread synchronization during device registration and connection abortion processes. The flaw manifests when multiple threads attempt concurrent operations on the same underlying data structures, creating a scenario that can lead to indefinite hangs and resource leaks. The issue specifically affects the interaction between io_uring_enter function execution, sqe registration, and the fuse_uring_create_ring_ent allocation process.
The technical root cause stems from improper ordering of operations during concurrent thread execution where thread a performs initial setup by allocating an entry without immediately acquiring the queue reference, while thread b simultaneously executes connection destruction logic. When thread b calls fuse_conn_destroy() followed by fuse_chan_abort(), it attempts to execute fuse_uring_abort() which becomes a no-op since the queue reference count remains zero at that moment. However, when thread a subsequently grabs the queue reference and continues execution, it creates a deadlock scenario where thread b's fuse_chan_wait_aborted() function enters an indefinite wait state, waiting for queue_refs to reach zero while no other process can decrement this counter.
This race condition directly relates to CWE-362 which describes concurrent execution issues that can lead to improper synchronization between threads. The vulnerability also maps to ATT&CK technique T1547.001 regarding registry run keys and startup programs, though in this context it represents a kernel-level thread synchronization failure rather than malicious persistence mechanisms. The fundamental problem occurs because the system fails to properly coordinate between registration operations and connection teardown procedures, creating an inconsistent state where cleanup operations cannot proceed correctly.
The operational impact of this vulnerability is severe as it can cause system instability and resource exhaustion through indefinite hanging processes that cannot be terminated by standard means. The affected system components include the io_uring subsystem, fuse filesystem implementation, and underlying kernel memory management structures. When triggered, the vulnerability leads to memory leaks where ring, queue, and entry structures remain allocated indefinitely, consuming system resources and potentially causing denial of service conditions.
The fix implements a proper ordering check that verifies the connection status under appropriate locking mechanisms after creating the entry and acquiring reference counts. This approach ensures that when thread a creates an entry and grabs a queue reference, it immediately checks whether the connection remains active through fch->connected verification under fch->lock protection. If the connection has been aborted during this critical section, the system properly releases resources and wakes up waiting processes in fuse_uring_do_register() rather than allowing indefinite blocking behavior.
The mitigation strategy involves proper synchronization between thread operations and ensures that all cleanup paths are properly coordinated through established kernel locking mechanisms. This fix prevents resource leaks by ensuring that when connections are aborted, all associated entries receive proper cleanup treatment either immediately during registration or through background async teardown workers. The solution maintains system stability by preventing the indefinite hang scenario while preserving the intended functionality of the fuse-uring subsystem and ensuring proper resource management under concurrent access conditions.