# CVE-2026-31584: media: mediatek: vcodec: fix use-after-free in encoder release path

> A use-after-free in the Linux kernel's MediaTek video encoder allows local attackers to execute arbitrary code or escalate privileges via a race condition.

- **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 Apr 2026
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2026-31584, DEBIAN-CVE-2026-31584, GHSA-5g36-g7f3-8q34, ROOT-OS-UBUNTU-2404-CVE-2026-31584, UBUNTU-CVE-2026-31584

## What is CVE-2026-31584?

CVE-2026-31584 is a high-severity use after free vulnerability in Linux kernel, published on 24 Apr 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:

media: mediatek: vcodec: fix use-after-free in encoder release path

The fops_vcodec_release() function frees the context structure (ctx)
without first cancelling any pending or running work in ctx->encode_work.
This creates a race window where the workqueue handler (mtk_venc_worker)
may still be accessing the context memory after it has been freed.

Race condition:

    CPU 0 (release path)               CPU 1 (workqueue)
    ---------------------               ------------------
    fops_vcodec_release()
      v4l2_m2m_ctx_release()
        v4l2_m2m_cancel_job()
        // waits for m2m job "done"
                                        mtk_venc_worker()
                                          v4l2_m2m_job_finish()
                                          // m2m job "done"
                                          // BUT worker still running!
                                          // post-job_finish access:
                                        other ctx dereferences
                                          // UAF if ctx already freed
        // returns (job "done")
      kfree(ctx)  // ctx freed

Root cause: The v4l2_m2m_ctx_release() only waits for the m2m job
lifecycle (via TRANS_RUNNING flag), not the workqueue lifecycle.
After v4l2_m2m_job_finish() is called, the m2m framework considers
the job complete and v4l2_m2m_ctx_release() returns, but the worker
function continues executing and may still access ctx.

The work is queued during encode operations via:
  queue_work(ctx->dev->encode_workqueue, &ctx->encode_work)
The worker function accesses ctx->m2m_ctx, ctx->dev, and other ctx
fields even after calling v4l2_m2m_job_finish().

This vulnerability was confirmed with KASAN by running an instrumented
test module that widens the post-job_finish race window. KASAN detected:

  BUG: KASAN: slab-use-after-free in mtk_venc_worker+0x159/0x180
  Read of size 4 at addr ffff88800326e000 by task kworker/u8:0/12

  Workqueue: mtk_vcodec_enc_wq mtk_venc_worker

  Allocated by task 47:
    __kasan_kmalloc+0x7f/0x90
    fops_vcodec_open+0x85/0x1a0

  Freed by task 47:
    __kasan_slab_free+0x43/0x70
    kfree+0xee/0x3a0
    fops_vcodec_release+0xb7/0x190

Fix this by calling cancel_work_sync(&ctx->encode_work) before kfree(ctx).
This ensures the workqueue handler is both cancelled (if pending) and
synchronized (waits for any running handler to complete) before the
context is freed.

Placement rationale: The fix is placed after v4l2_ctrl_handler_free()
and before list_del_init(&ctx->list). At this point, all m2m operations
are done (v4l2_m2m_ctx_release() has returned), and we need to ensure
the workqueue is synchronized before removing ctx from the list and
freeing it.

Note: The open error path does NOT need cancel_work_sync() because
INIT_WORK() only initializes the work structure - it does not schedule
it. Work is only scheduled later during device_run() operations.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-31584?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31584?

Apply the vendor's patch.

## Is CVE-2026-31584 being exploited?

There is no known exploitation of CVE-2026-31584 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-31584 and fix it if it is affected.

What it is: CVE-2026-31584 is a high-severity use after free vulnerability in Linux kernel, published on 24 Apr 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-2026-31584 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-31584/ (Markdown: https://insights.sbomify.com/CVE-2026-31584/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31584
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31584
- OSV: https://osv.dev/vulnerability/CVE-2026-31584

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31584/
Summaries are generated and may contain mistakes; the official description above is the record.