---
id: "CVE-2026-99035"
kind: "vulnerability"
aliases: ["CVE-2026-99035"]
title: "Linux MediaTek MMC driver: use-after-free when unbinding the host"
severity: "unknown"
cvss: null
epss: 0.00209
exploited: false
status: "open"
category: "infrastructure"
products: []
ecosystems: []
tags: ["embedded", "infrastructure", "kernel", "linux", "mediatek"]
not_affected_if: ["driver-never-unbound", "no-mediatek-hardware"]
published_at: "2026-10-23T13:17:26+00:00"
first_seen_at: "2026-10-23T21:57:33+00:00"
updated_at: "2026-10-25T12:38:50+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-99035", "first_seen_at": "2026-10-23T21:57:33+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-99035", "first_seen_at": "2026-10-25T12:38:50+00:00"}]
---

# Linux MediaTek MMC driver: use-after-free when unbinding the host

In the Linux kernel's MediaTek mtk-sd MMC driver, a pending request timeout callback can run after the driver is removed, touching freed host memory. The description reports KASAN use-after-free reports during unbind tests, so the likely effect is a kernel crash or memory corruption on unbind.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check whether the MediaTek mtk-sd MMC driver is loaded, for example with `lsmod | grep mtk_sd` or by looking for an mtk-sd device bound under /sys/bus/platform/drivers/.
- Compare the running kernel with the fixed release: `uname -r`.

## Fix

- Update to a Linux kernel release that includes the upstream commit adding cancel_delayed_work_sync() to msdc_drv_remove (version unknown from the sources).

## Timeline

- 2026-10-23T21:57:33+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-99035
- 2026-10-25T12:38:50+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-99035

## From the sources

In the Linux kernel, the following vulnerability has been resolved:

mmc: mtk-sd: Cancel request timeout work on remove

The driver queues req_timeout while a request is active.
msdc_request_done() uses cancel_delayed_work(), which does not wait for
a timeout callback that has already started.

The timeout callback calls mmc_request_done(), which wakes the request
waiter, and then continues to use host->dev_comp and check the SDIO IRQ.
During unbind, msdc_drv_remove() can return and the managed mmc_host can
be freed before the callback finishes.

KASAN reported use-after-free accesses in msdc_request_done() and
msdc_recheck_sdio_irq() in each of three unbind tests.  The same tests
completed without a kernel diagnostic after this change.

Call cancel_delayed_work_sync() after mmc_remove_host() has stopped new
requests and before the driver releases the host resources.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_