CVE-2026-74575 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
thunderbolt: Prevent XDomain delayed work use-after-free on disconnect
tb_xdp_handle_request() runs on system_wq and queues xd->state_work via queue_delayed_work() in three request handlers: PROPERTIES_CHANGED_REQUEST, UUID_REQUEST (via start_handshake), and LINK_STATE_CHANGE_REQUEST. Similarly, update_xdomain() queues xd->properties_changed_work when local properties change.
Concurrently, tb_xdomain_remove() calls stop_handshake() which does cancel_delayed_work_sync() on both delayed works. Later, tb_xdomain_unregister() calls device_unregister() which eventually frees the xdomain. Since commit 559c1e1e0134 ("thunderbolt: Run tb_xdp_handle_request() in system workqueue") moved the request handler off tb->wq, the handler and the remove path are no longer serialized. If queue_delayed_work() executes after cancel_delayed_work_sync() but before the xdomain is freed, the delayed work fires on a freed object.
Add xd->removing that tb_xdomain_remove() sets under xd->lock before calling stop_handshake(). Each external queue site holds the same lock and checks removing before calling queue_delayed_work(). This provides the mutual exclusion needed: either the queue site acquires the lock first and queues work that the subsequent cancel will see, or the remove path acquires the lock first and the queue site observes removing == true and skips the queue.
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Analysis
by VulDB Data Team • 08/16/2026
The vulnerability under discussion involves a use-after-free condition in the Linux kernel's thunderbolt subsystem specifically within the thunderbolt driver's xdomain handling mechanism. This flaw occurs in the context of Thunderbolt device management where the kernel must coordinate between asynchronous workqueue operations and device removal procedures. The issue manifests when multiple execution paths attempt to access the same memory object without proper synchronization, creating a scenario where freed memory can be accessed by delayed work items that were scheduled prior to the object's deallocation.
The technical root cause stems from a race condition between the thunderbolt workqueue handler tb_xdp_handle_request() and the device removal sequence. This handler executes on the system_wq workqueue and schedules delayed work items through queue_delayed_work() in response to three different request types: PROPERTIES_CHANGED_REQUEST, UUID_REQUEST, and LINK_STATE_CHANGE_REQUEST. Additionally, update_xdomain() schedules properties_changed_work when local properties change. The synchronization problem emerged after commit 559c1e1e0134 which moved the request handler from tb->wq to system_wq, breaking the previously implicit serialization between these execution paths.
The operational impact of this vulnerability is significant as it allows for potential arbitrary code execution or system crashes when a Thunderbolt device is disconnected while work items are pending. The race condition occurs because tb_xdomain_remove() calls stop_handshake() which cancels delayed work items using cancel_delayed_work_sync(), but this cancellation happens before the actual device memory is freed by tb_xdomain_unregister(). If queue_delayed_work() executes after the cancellation but before device_unregister() frees the xdomain object, the delayed work will attempt to execute on freed memory. This represents a classic use-after-free vulnerability that can be exploited to gain unauthorized access or cause system instability.
The mitigation implemented addresses this through proper mutual exclusion using a new xd->removing flag that is set by tb_xdomain_remove() under the xdomain's lock before calling stop_handshake(). This approach ensures that all external queue sites must acquire the same lock and check the removing flag before calling queue_delayed_work(), creating a clear serialization mechanism. This solution aligns with common security practices for preventing race conditions in kernel code and follows established patterns for handling concurrent access to shared resources, effectively preventing the scenario where delayed work items could execute against freed memory structures.
This vulnerability classifies as a use-after-free condition under CWE-416 and represents a privilege escalation vector that could be exploited by malicious actors with physical access to Thunderbolt ports. The fix demonstrates proper kernel security engineering practices by implementing fine-grained locking mechanisms around shared resources, preventing the race condition between workqueue operations and device removal sequences. The solution maintains system stability while preserving the intended functionality of the thunderbolt subsystem's asynchronous processing capabilities.