CVE-2026-64340 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
USB: legousbtower: 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
This vulnerability resides in the Linux kernel's USB subsystem, specifically within the legousbtower driver implementation. The issue manifests as a use-after-free condition that occurs during device disconnection scenarios, representing a critical reliability and potential security concern for embedded systems and IoT devices utilizing USB peripherals. The flaw demonstrates how improper synchronization mechanisms can lead to memory corruption vulnerabilities that may be exploited by malicious actors.
The technical root cause stems from the inappropriate use of mutex_unlock() for managing object lifetime in kernel space. Unlike spinlocks and reference counting mechanisms, mutex_unlock() does not provide atomic guarantees regarding object access after lock release, creating a race condition window where the mutex structure may still be accessed after being freed. This fundamental misunderstanding of locking semantics leads to undefined behavior when the driver's cleanup routines execute concurrently with device disconnection events.
The operational impact of this vulnerability extends beyond simple system instability to potentially enable privilege escalation or denial-of-service conditions in embedded environments. When a USB device disconnects while the driver is processing operations, the race condition between the release() callback and disconnect() handler can result in memory corruption that may be exploited to execute arbitrary code with kernel privileges. This scenario particularly affects systems where USB devices are frequently connected and disconnected, such as industrial control systems or network appliances.
The proposed mitigation strategy involves implementing a kref (kernel reference counting) mechanism to properly manage the driver data lifetime instead of relying on mutex_unlock() for object destruction. This approach ensures that resources remain valid until all references are explicitly released, eliminating the race condition window where memory could be accessed after deallocation. The solution aligns with established kernel development practices and addresses the core issue identified in the kernel's locking documentation references, which specifically warn against using sleeping locks like mutex_unlock() for direct object lifetime management.
This vulnerability classification maps to CWE-415: Double Free and CWE-416: Use After Free within the Common Weakness Enumeration framework, representing a classic memory safety issue in kernel space. The ATT&CK framework would categorize this under T1068: Exploitation for Privilege Escalation and T1499: Endpoint Denial of Service, as the vulnerability could enable both privilege escalation through code execution and system availability disruption. The fix demonstrates proper kernel development practices by utilizing established reference counting mechanisms that are specifically designed to handle concurrent access patterns in kernel drivers, ensuring memory safety while maintaining proper resource lifecycle management.