CVE-2026-64261 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
fuse-uring: Avoid use-after-free in fuse_uring_async_stop_queues
fuse_uring_async_stop_queues() might run when the last reference on ring->queue_refs was already dropped.
In order to avoid an early destruction a reference on struct fuse_conn is now taken before starting fuse_uring_async_stop_queues() and that reference is only released when that delayed work queue terminates.
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Analysis
by VulDB Data Team • 07/25/2026
This vulnerability resides within the Linux kernel's fuse subsystem particularly affecting the unified io-uring implementation known as fuse-uring. The issue manifests in the fuse_uring_async_stop_queues function which handles cleanup operations for asynchronous I/O queues. When this function executes, it may encounter a scenario where the reference counter for ring->queue_refs has already reached zero, indicating that all references to the queue structures have been released. This premature state transition creates a dangerous condition where the function attempts to operate on memory that may have already been deallocated.
The technical flaw stems from improper reference counting management within the kernel's asynchronous I/O processing framework. Specifically, when fuse_uring_async_stop_queues() is invoked as part of a delayed work queue execution, it accesses resources that could have been freed by concurrent operations. This represents a classic use-after-free vulnerability pattern where memory access occurs after the memory has been returned to the system pool. The problem directly relates to CWE-416 which categorizes improper free conditions and improper cleanup issues in memory management.
The operational impact of this vulnerability extends beyond simple memory corruption. An attacker who can trigger the specific sequence leading to this condition could potentially exploit it to achieve arbitrary code execution within kernel space or cause system instability through denial of service attacks. The vulnerability is particularly concerning because it operates at the kernel level where such issues can compromise entire system security and stability. The attack surface becomes more significant when considering that fuse-uring is designed for high-performance I/O operations and may be utilized in critical system components.
The fix implemented addresses this by introducing proper reference counting protocols before initiating the cleanup process. A reference to the struct fuse_conn structure is now explicitly acquired before starting the fuse_uring_async_stop_queues() function execution. This ensures that the connection structure remains valid throughout the entire cleanup lifecycle. The reference is only released once the delayed work queue has fully terminated, creating a clear temporal boundary between resource allocation and deallocation phases. This mitigation approach aligns with standard kernel security practices for preventing use-after-free conditions in concurrent environments.
From an ATT&CK framework perspective, this vulnerability could be categorized under privilege escalation techniques when exploited by malicious actors who gain access to the system through other means. The fix demonstrates adherence to defensive programming principles and proper resource management that are essential for maintaining kernel integrity. The solution reflects best practices in Linux kernel development where reference counting and synchronization mechanisms must account for all possible execution paths and timing conditions. This vulnerability underscores the complexity of managing asynchronous operations in kernel space where multiple threads and delayed work queues can interact in unpredictable ways, requiring careful consideration of memory lifecycle management throughout the system's operation.