CVE-2026-74613 in Linux
Summary
by MITRE • 08/22/2026
In the Linux kernel, the following vulnerability has been resolved:
vsock/virtio: avoid refilling the RX queue after teardown
Commit b917507e5ad9 ("vsock/virtio: stop workers during the .remove()") made the RX worker jump to its common exit when rx_run is clear. That exit still refills the RX queue when the buffer count is low, so work queued across virtio_vsock_vqs_del() can add buffers after the virtqueues have been deleted.
BUG: KASAN: slab-use-after-free in virtqueue_add_sgs Read of size 4 by task kworker/0:1 Workqueue: virtio_vsock virtio_transport_rx_work Call Trace: virtqueue_add_sgs (drivers/virtio/virtio_ring.c:2796) virtio_vsock_rx_fill (net/vmw_vsock/virtio_transport.c:332) virtio_transport_rx_work (net/vmw_vsock/virtio_transport.c:701) process_one_work (kernel/workqueue.c:3314) worker_thread (kernel/workqueue.c:3478) kthread (kernel/kthread.c:436) ret_from_fork (arch/x86/kernel/process.c:158) ret_from_fork_asm (arch/x86/entry/entry_64.S:245) ... Freed by task 141: kfree (mm/slub.c:6566) vp_del_vq (drivers/virtio/virtio_pci_common.c:259) vp_del_vqs (drivers/virtio/virtio_pci_common.c:285) virtio_vsock_freeze (net/vmw_vsock/virtio_transport.c:912) virtio_device_freeze (drivers/virtio/virtio.c:658) virtio_pci_freeze (drivers/virtio/virtio_pci_common.c:601) pci_pm_freeze (drivers/pci/pci-driver.c:1098) device_suspend (drivers/base/power/main.c:1968) Kernel panic - not syncing: KASAN: panic_on_warn set ...
Jump to a no-refill exit when rx_run is clear, leaving the normal exit to replenish a running queue.
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Analysis
by VulDB Data Team • 08/22/2026
The vulnerability identified in the Linux kernel involves a race condition within the virtio vsock transport implementation that leads to a use-after-free error during device teardown or suspension operations. This issue stems from improper synchronization between the worker threads responsible for processing incoming network packets and the lifecycle management of the underlying virtual hardware queues. Specifically, when the system initiates a freeze event such as PCI power state transition or driver removal, the virtio vsock module attempts to stop its background workers by clearing the rx_run flag. While this action successfully halts new work items from being queued for execution, it fails to account for work items that are already in progress on CPU cores. These lingering worker threads continue their execution path and eventually reach a point where they attempt to refill the receive queue with available buffers to maintain throughput capacity.
The critical technical flaw lies in the fact that this refilling process interacts directly with virtio virtual queues, which have already been deallocated by the time these late-arriving work items execute. The kernel's memory management subsystem has freed the slab objects associated with these virtqueues during the vp_del_vqs routine invoked as part of the device freeze sequence. Consequently, when the worker thread calls virtqueue_add_sgs to add scatter-gather lists back into the queue structure, it accesses memory that is no longer valid or mapped for use by the driver. This access triggers a Kernel Address Sanitizer (KASAN) report indicating a slab-use-after-free condition, where the kernel attempts to read from a freed memory region. The severity of this flaw is compounded by the fact that many distributions configure panic_on_warn, causing such detection events to escalate into immediate system panics and crashes rather than simple warnings or logged errors.
From an operational perspective, this vulnerability can be triggered during standard power management cycles, including suspend-to-RAM operations or hot-unplug scenarios for virtual machines utilizing virtio interfaces. An attacker with local access who can induce frequent device removals or state changes could potentially cause denial of service by repeatedly crashing the host system. Although remote exploitation is unlikely given that this requires specific kernel-level race conditions during teardown rather than network packet processing, the stability impact on cloud infrastructure and virtualized environments remains significant. The crash occurs within the context of a workqueue thread, which means it does not directly compromise user-space applications but destabilizes the entire operating system instance hosting them.
This vulnerability maps to CWE-416, Use After Free, as the core issue is accessing memory after it has been released back to the allocator. In terms of attack patterns, this aligns with MITRE ATT&CK technique T1079, System Service Discovery or more broadly system availability impacts through resource exhaustion and instability, though primarily classified under reliability flaws rather than active exploitation techniques. The root cause is a synchronization gap where the logical state indicating that work should stop does not prevent currently executing threads from completing their current operations which depend on resources being cleaned up concurrently.
To mitigate this vulnerability, it is essential to ensure that all pending work items are fully flushed and completed before any hardware resources or data structures associated with those tasks are deallocated. The fix involves modifying the exit logic in the virtio vsock receive worker so that when rx_run is cleared, the thread jumps directly to a no-refill exit path rather than proceeding to refill buffers. This ensures that once the decision is made to tear down the device, no further attempts are made to interact with the now-invalid virtual queue structures. System administrators should apply kernel updates containing this patch immediately in environments where virtio devices are subject to dynamic power management or hot-plug events. Regularly updating the Linux kernel and associated virtio drivers ensures that these synchronization primitives are correctly implemented, preventing race conditions during device lifecycle transitions.