CVE-2026-64343 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
USB: ldusb: fix use-after-free on disconnect race
mutex_unlock() may access the mutex structure after releasing the lock and therefore cannot be used to manage lifetime of objects directly (unlike spinlocks and refcounts). [1][2]
Use a kref to release the driver data to avoid use-after-free in mutex_unlock() when release() races with disconnect().
[1] a51749ab34d9 ("locking/mutex: Document that mutex_unlock() is
non-atomic") [2] 2b9d9e0a9ba0 ("locking/mutex: Clarify that mutex_unlock(), and most
other sleeping locks, can still use the lock object after it's unlocked")
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Analysis
by VulDB Data Team • 07/25/2026
The vulnerability identified in the Linux kernel represents a critical use-after-free condition within the USB ldusb driver implementation that arises during device disconnection scenarios. This flaw stems from improper synchronization mechanisms when managing the lifecycle of driver data structures, specifically involving mutex unlock operations that can access memory regions after they have been released. The issue manifests when the release() function executes concurrently with disconnect() operations, creating a race condition that violates fundamental memory safety principles.
The technical root cause of this vulnerability lies in the inappropriate use of mutex_unlock() for managing object lifetime, a pattern that directly contradicts established locking best practices and kernel security guidelines. Unlike spinlocks or reference counters which provide atomic guarantees for memory management, mutex_unlock() operations can access the mutex structure after releasing the lock, creating a window where freed memory may still be accessed. This behavior was explicitly documented in kernel commits a51749ab34d9 and 2b9d9e0a9ba0, which clarified that sleeping locks like mutexes cannot be relied upon for direct object lifetime management. The ldusb driver failed to account for this fundamental limitation, leading to potential memory corruption when concurrent disconnect operations occurred.
The operational impact of this vulnerability extends beyond simple memory corruption, potentially enabling privilege escalation and system instability within the USB subsystem. When a device disconnects while the release() function is executing concurrently, the use-after-free condition can result in arbitrary code execution or denial of service attacks targeting the USB driver framework. This represents a significant security risk as it allows malicious actors to exploit the race condition through USB device manipulation, potentially compromising system integrity and availability. The vulnerability affects systems running affected Linux kernel versions where USB ldusb drivers are active and handles concurrent device disconnection scenarios.
Mitigation strategies for this vulnerability require implementing proper reference counting mechanisms using kref structures instead of relying on mutex_unlock() for object lifetime management. The recommended approach involves transitioning from direct mutex-based lifetime control to atomic reference counting that properly tracks object usage across concurrent operations. This solution aligns with common security practices outlined in the CWE catalog under CWE-416: Use After Free, which specifically addresses the dangers of accessing memory after it has been freed. Additionally, this remediation approach follows ATT&CK framework techniques related to privilege escalation and system exploitation, ensuring that the fix addresses both immediate security concerns and broader kernel stability requirements.
The implementation of kref-based management ensures that driver data remains valid until all references are explicitly released, eliminating the race condition between disconnect() and release() operations. This approach provides atomic guarantees necessary for concurrent access patterns while maintaining proper object lifecycle management within the USB subsystem. The fix demonstrates adherence to Linux kernel security best practices and addresses fundamental locking model limitations that could otherwise lead to more severe system compromise scenarios. Regular kernel updates and security patches should be applied to ensure all systems remain protected against this and similar race condition vulnerabilities in kernel driver implementations.