# CVE-2026-43327: USB: dummy-hcd: Fix locking/synchronization error

> A race condition in the Linux kernel USB dummy-hcd driver allows a local attacker to trigger a system crash via a null pointer dereference.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 8 May 2026
- **Updated:** 23 May 2026
- **Also known as:** BELL-CVE-2026-43327, DEBIAN-CVE-2026-43327, GHSA-mhgr-c53r-gx3p, ROOT-OS-DEBIAN-11-CVE-2026-43327, ROOT-OS-UBUNTU-2204-CVE-2026-43327, ROOT-OS-UBUNTU-2404-CVE-2026-43327, UBUNTU-CVE-2026-43327

## What is CVE-2026-43327?

CVE-2026-43327 is a medium-severity vulnerability in Linux kernel, published on 8 May 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: dummy-hcd: Fix locking/synchronization error

Syzbot testing was able to provoke an addressing exception and crash
in the usb_gadget_udc_reset() routine in
drivers/usb/gadgets/udc/core.c, resulting from the fact that the
routine was called with a second ("driver") argument of NULL.  The bad
caller was set_link_state() in dummy_hcd.c, and the problem arose
because of a race between a USB reset and driver unbind.

These sorts of races were not supposed to be possible; commit
7dbd8f4cabd9 ("USB: dummy-hcd: Fix erroneous synchronization change"),
along with a few followup commits, was written specifically to prevent
them.  As it turns out, there are (at least) two errors remaining in
the code.  Another patch will address the second error; this one is
concerned with the first.

The error responsible for the syzbot crash occurred because the
stop_activity() routine will sometimes drop and then re-acquire the
dum->lock spinlock.  A call to stop_activity() occurs in
set_link_state() when handling an emulated USB reset, after the test
of dum->ints_enabled and before the increment of dum->callback_usage.
This allowed another thread (doing a driver unbind) to sneak in and
grab the spinlock, and then clear dum->ints_enabled and dum->driver.
Normally this other thread would have to wait for dum->callback_usage
to go down to 0 before it would clear dum->driver, but in this case it
didn't have to wait since dum->callback_usage had not yet been
incremented.

The fix is to increment dum->callback_usage _before_ calling
stop_activity() instead of after.  Then the thread doing the unbind
will not clear dum->driver until after the call to
usb_gadget_udc_reset() safely returns and dum->callback_usage has been
decremented again.

Weakness: CWE-667 (Improper Locking)

## Which versions are affected by CVE-2026-43327?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-43327?

Apply the vendor's patch.

## Is CVE-2026-43327 being exploited?

There is no known exploitation of CVE-2026-43327 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-2026-43327 and fix it if it is affected.

What it is: CVE-2026-43327 is a medium-severity vulnerability in Linux kernel, published on 8 May 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-2026-43327 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-2026-43327/ (Markdown: https://insights.sbomify.com/CVE-2026-43327/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43327
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43327
- OSV: https://osv.dev/vulnerability/CVE-2026-43327

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43327/
Summaries are generated and may contain mistakes; the official description above is the record.