# CVE-2026-31584

> Vulnerability · severity: **HIGH** (CVSS 7.8).

## 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 ta

## Key facts

- **CVE ID:** CVE-2026-31584
- **Published:** 2026-04-24
- **CVSS severity:** HIGH
- **CVSS base score:** 7.8
- **CWE codes:** CWE-416

## Affected products

- `linux:linux_kernel`

## Primary sources

- NIST NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31584

## Citation

> AI Analytics. CVE-2026-31584. Retrieved 2026-07-30 from https://api.ai-analytics.org/cve/CVE-2026-31584. Derived from NIST NVD. Licensed CC0.

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