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

> A race condition in the Linux kernel's ACRN virtualization driver allows a use-after-free, potentially enabling local attackers to execute code or escalate privileges.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-103679, BELL-CVE-2026-97478, DEBIAN-CVE-2026-97478, GHSA-97q3-wcm5-m49q, UBUNTU-CVE-2026-97478

## What is CVE-2026-97478?

CVE-2026-97478 is a high-severity use after free vulnerability in Linux, published on 24 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official 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.

## Which versions are affected by CVE-2026-97478?


## How do I fix CVE-2026-97478?

Apply the vendor's patch.

## Is CVE-2026-97478 being exploited?

There is no known exploitation of CVE-2026-97478 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-97478 and fix it if it is affected.

What it is: CVE-2026-97478 is a high-severity use after free vulnerability in Linux, published on 24 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-97478 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-97478/ (Markdown: https://insights.sbomify.com/CVE-2026-97478/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-97478
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-97478
- OSV: https://osv.dev/vulnerability/CVE-2026-97478

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-97478/
Summaries are generated and may contain mistakes; the official description above is the record.