# CVE-2026-97992: vhost-vdpa: protect config_ctx from being freed under the config callback

> A use-after-free in the Linux kernel vhost-vdpa driver allows local attackers with root access to execute arbitrary code or escalate privileges via race conditions.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-104819, BELL-CVE-2026-97992, DEBIAN-CVE-2026-97992, GHSA-hm65-mv9r-74m7, UBUNTU-CVE-2026-97992

## What is CVE-2026-97992?

CVE-2026-97992 is an use after free vulnerability in Linux, published on 25 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:

vhost-vdpa: protect config_ctx from being freed under the config callback

vhost_vdpa_config_cb() loads v->config_ctx and signals it without taking
a reference and without holding any lock:

	struct eventfd_ctx *config_ctx = v->config_ctx;

	if (config_ctx)
		eventfd_signal(config_ctx);

VHOST_VDPA_SET_CONFIG_CALL replaces that field and drops what is normally
the last reference to the old context:

	swap(ctx, v->config_ctx);

	if (ctx)
		eventfd_ctx_put(ctx);

eventfd_ctx_put() drops the last kref and frees the context immediately,
with no RCU grace period, so a callback that has already loaded the
pointer goes on to dereference freed memory.  The two sides share no
lock: the ioctl runs under vhost_dev.mutex, while the parent invokes the
callback from its own interrupt or workqueue context.

This is not the reopen refcount underflow fixed by commit f6bbf0010ba0
("vhost-vdpa: fix use-after-free of v->config_ctx"), which was about
vhost_vdpa_config_put() leaving a stale pointer behind.  Here the pointer
is maintained correctly and it is the read side that is unprotected.

With VDUSE as the parent this is reachable from userspace with access to
/dev/vduse (root by default).  VDUSE_DEV_INJECT_CONFIG_IRQ queues
dev->inject, and vduse_dev_irq_inject() runs the callback under VDUSE's
own dev->irq_lock, which vhost does not hold.  vduse_dev_reset() does
flush_work(&dev->inject), but VHOST_VDPA_SET_CONFIG_CALL never goes
through reset, so an inject already in flight is not waited for.  A
process that injects config interrupts on the VDUSE fd while another
thread swaps the call fd on the vhost-vdpa fd hits it in seconds:

  BUG: KASAN: slab-use-after-free in native_queued_spin_lock_slowpath
  Read of size 4 at addr ffff888107d21808 by task kworker/u17:1/2993
  Workqueue: vduse-irq vduse_dev_irq_inject
  Call Trace:
   native_queued_spin_lock_slowpath+0x97/0x5b0
   _raw_spin_lock_irqsave+0xd4/0xe0
   eventfd_signal_mask+0x69/0x120
   vhost_vdpa_config_cb+0x34/0x50
   vduse_dev_irq_inject+0x46/0x60
   process_one_work+0x468/0x950

  Allocated by task 2992:
   do_eventfd+0x50/0x200
   __x64_sys_eventfd2+0x2e/0x40

  Freed by task 2992:
   eventfd_ctx_put+0xb9/0xc0
   vhost_vdpa_unlocked_ioctl+0x116c/0x2190

Add a spinlock covering every access to config_ctx, so the callback
either signals a context that is still alive or observes NULL, and the
put happens only once no callback can reach the old value.

Clearing the parent's callback before the put would not be enough: of the
in-tree set_config_cb() implementations only VDUSE takes a lock, the rest
store the pointer unlocked, so that would not order against an in-flight
invocation.

## Which versions are affected by CVE-2026-97992?


## How do I fix CVE-2026-97992?

Apply the vendor's patch.

## Is CVE-2026-97992 being exploited?

There is no known exploitation of CVE-2026-97992 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-97992 and fix it if it is affected.

What it is: CVE-2026-97992 is an use after free vulnerability in Linux, published on 25 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-2026-97992 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-2026-97992/ (Markdown: https://insights.sbomify.com/CVE-2026-97992/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-97992
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-97992
- OSV: https://osv.dev/vulnerability/CVE-2026-97992

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-97992/
Summaries are generated and may contain mistakes; the official description above is the record.