# CVE-2026-89738: usb: gadget: at91_udc: drain polled-VBUS timer/work before udc is freed

> A use-after-free vulnerability in the Linux kernel's at91_udc USB gadget driver allows attackers to cause a denial of service or potentially execute code during driver unbind.

- **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:** 11 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-100542, BELL-CVE-2026-89738, DEBIAN-CVE-2026-89738, GHSA-3f57-g7j5-hj3q, UBUNTU-CVE-2026-89738

## What is CVE-2026-89738?

CVE-2026-89738 is a high-severity use after free vulnerability in Linux, published on 11 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:

usb: gadget: at91_udc: drain polled-VBUS timer/work before udc is freed

In polled-VBUS mode (board.vbus_pin && board.vbus_polled), probe arms a
self-restarting cycle: at91_vbus_timer() schedules vbus_timer_work, and
at91_vbus_timer_work() calls at91_vbus_update() and re-arms the timer via
mod_timer(). Both recover the same udc through container_of and dereference
it on every iteration.

Neither teardown path cancels this cycle. udc is devm-allocated, so it is
freed after at91udc_remove() returns, and is likewise freed when probe
fails and devres runs. A timer callback or work item that is pending or
running at either point dereferences the freed udc.

Add at91_udc_shutdown_vbus_timer() and call it from at91udc_remove() and
from the usb_add_gadget_udc() failure path in probe; the remaining probe
error paths fail before the timer is armed. timer_shutdown_sync() waits
for a running callback and clears timer->function, which makes the work
handler's mod_timer() a permanent no-op; cancel_work_sync() then drains
any pending or running work whose re-arm attempt now does nothing. The
timer must be shut down first, since cancelling the work alone would let
the timer re-queue it. The guard mirrors probe: in IRQ mode the timer and
work_struct are never initialized.

This does not require a fault; a normal driver unbind can interleave with
an already queued work item.

This issue was found by an in-house static analysis tool.

## Which versions are affected by CVE-2026-89738?


## How do I fix CVE-2026-89738?

Apply the vendor's patch.

## Is CVE-2026-89738 being exploited?

There is no known exploitation of CVE-2026-89738 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89738 and fix it if it is affected.

What it is: CVE-2026-89738 is a high-severity use after free vulnerability in Linux, published on 11 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-2026-89738 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-2026-89738/ (Markdown: https://insights.sbomify.com/CVE-2026-89738/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89738
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89738
- OSV: https://osv.dev/vulnerability/CVE-2026-89738

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89738/
Summaries are generated and may contain mistakes; the official description above is the record.