# CVE-2026-97478: virt: acrn: Fix irqfd use-after-free during eventfd shutdown

CVE-2026-97478 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-97478, released September 24, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-97478
- Priority: High
- CVSS: 7.8 (Moderate)
- EPSS: 0.0013
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 24, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-97478

## Description

In the Linux kernel, the following vulnerability has been resolved:  virt: acrn: Fix irqfd use-after-free during eventfd shutdown  acrn_irqfd_deassign() and the eventfd EPOLLHUP wakeup can race and free the same struct hsm_irqfd:    CPU0                                 CPU1   ----                                 ----   eventfd_release()     wake_up_poll(EPOLLHUP)       hsm_irqfd_wakeup()         queue_work(&irqfd->shutdown)                                        acrn_irqfd_deassign()                                          hsm_irqfd_shutdown()                                            list_del_init()                                            eventfd_ctx_remove_wait_queue()                                            eventfd_ctx_put()                                          kfree(irqfd)   hsm_irqfd_shutdown_work()     container_of(work, ..., shutdown)     irqfd->vm                  <-- use-after-free  The deassign path freed the irqfd while a shutdown work item was already queued by EPOLLHUP (or vice versa), so the work item could resurrect a dangling pointer through container_of().  Switch to the lifetime model used by KVM irqfds:   - Deassign/deinit only deactivate the irqfd: remove it from vm->irqfds    under irqfds_lock and queue the cleanup work.  - hsm_irqfd_shutdown_work() becomes the sole owner that unhooks the    eventfd waitqueue entry, drops the eventfd reference and frees the    irqfd.  - A new HSM_IRQFD_FLAG_SHUTDOWN bit guarded by test_and_set_bit()    ensures the cleanup work is queued at most once, no matter how many    of {EPOLLHUP, deassign, deinit} fire concurrently.  This is safe to    call from the waitqueue callback, which runs with wqh->lock held and    IRQs disabled and therefore cannot take irqfds_lock.  - acrn_irqfd_deassign() flushes vm->irqfd_wq before returning so the    eventfd is fully detached on return.  acrn_irqfd_deinit() deactivates    every irqfd, flushes the workqueue and only then destroys it, so no    path can queue_work() onto a torn-down workqueue.  - acrn_irqfd_assign() now installs the eventfd waitqueue entry and    publishes the irqfd to vm->irqfds under irqfds_lock, so the irqfd is    never visible to deassign/deinit before its waitqueue entry is in    place, and any EPOLLHUP that fires in the assign window queues    cleanup work that blocks on irqfds_lock until publication is done.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-97478](https://patchblox.com/security/data/fix/linux/debian-cve-2026-97478.md) | Sep 24, 2026 |
| Linux | linux Debian 14 | 7.2.6-1 | [DEBIAN-CVE-2026-97478](https://patchblox.com/security/data/fix/linux/debian-cve-2026-97478.md) | Sep 24, 2026 |

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Data as of 2026-11-08T06:59:42Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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