---
id: "CVE-2026-99039"
kind: "vulnerability"
aliases: ["CVE-2026-99039"]
title: "Linux kernel: memstick timeout frees card still used by driver"
severity: "unknown"
cvss: null
epss: 0.00209
exploited: false
status: "open"
category: "infrastructure"
products: []
ecosystems: []
tags: ["infrastructure", "linux-kernel", "memstick", "self-hosted"]
not_affected_if: ["memstick-modules-not-loaded", "no-memstick-hardware"]
published_at: "2026-10-23T13:17:27+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-2026-99039", "first_seen_at": "2026-10-23T21:57:33+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-99039", "first_seen_at": "2026-10-25T12:38:50+00:00"}]
---

# Linux kernel: memstick timeout frees card still used by driver

The memstick core stops waiting for a pending card request after a timeout and frees the card structure while the host controller driver can still write into it. This is a use-after-free that KASAN reports as a write into freed slab memory.

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

## How to check

- Check whether the kernel includes the memstick fix by looking for `wait_for_completion(` without `_timeout` in `drivers/memstick/core/memstick.c` in the source tree
- Check whether memstick hardware such as rtsx_usb_ms is in use with `lsmod | grep -E 'rtsx_usb_ms|memstick'`

## Fix

- Update the Linux kernel to a release that includes the commit replacing `wait_for_completion_timeout()` with `wait_for_completion()` in memstick_set_rw_addr() and memstick_alloc_card()
- Versions are unknown from the sources

## Timeline

- 2026-10-23T21:57:33+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-99039
- 2026-10-25T12:38:50+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-99039

## From the sources

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

memstick: core: wait for request completion before freeing card

In memstick_alloc_card() and memstick_set_rw_addr(),
wait_for_completion_timeout() is used to wait for device identification
and address configuration requests to complete.

The memstick subsystem does not provide an abort or cancellation
callback in struct memstick_host for in-flight requests. If
wait_for_completion_timeout() expires (for instance, when a USB transfer
or command retry is delayed), memstick_alloc_card() returns an error and
frees the memstick_dev structure via kfree(card).

However, the host controller driver (such as rtsx_usb_ms) is still
running the request asynchronously in worker context. When the transfer
eventually finishes, the driver writes into host->req->data, which
points to memory inside the already freed card structure. This leads to
a KASAN slab-use-after-free write:

  BUG: KASAN: slab-use-after-free in ms_read_bytes+0x8fe/0x990
  Write of size 1 at addr ffff88813c188079 by task kworker/1:5/5239
  Workqueue: events rtsx_usb_ms_handle_req
  Call Trace:
   ms_read_bytes+0x8fe/0x990 drivers/memstick/host/rtsx_usb_ms.c:450
   rtsx_usb_ms_issue_cmd drivers/memstick/host/rtsx_usb_ms.c:477 [inline]
   rtsx_usb_ms_handle_req+0x557/0x1a00 drivers/memstick/host/rtsx_usb_ms.c:531
   process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
   worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
   kthread+0x373/0x450 kernel/kthread.c:436

  Allocated by task 1662:
   memstick_alloc_card drivers/memstick/core/memstick.c:383 [inline]
   memstick_check+0x2c1/0x10d0 drivers/memstick/core/memstick.c:452
   process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396

  Freed by task 1662:
   kfree+0x20c/0x650 mm/slub.c:6792
   memstick_alloc_card drivers/memstick/core/memstick.c:420 [inline]
   memstick_check+0x72b/0x10d0 drivers/memstick/core/memstick.c:452
   process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396

Host controller drivers (rtsx_usb_ms, jmb38x_ms, tifm_ms, r592) already
implement their own hardware and bus timeouts, and callers in
mspro_block and ms_block already rely on wait_for_completion()
unconditionally.

Replace wait_for_completion_timeout() with wait_for_completion() in
memstick_set_rw_addr() and memstick_alloc_card() so that the card
structure is never freed while an asynchronous request is in flight.

---

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