# CVE-2026-63874: net: mctp: usb: fix race between urb completion and rx_retry cancellation

> A race condition in the Linux kernel MCTP USB driver can lead to a denial of service by improperly handling URB completion and work cancellation.

- **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:** 19 Jul 2026
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2026-63874, DEBIAN-CVE-2026-63874, GHSA-4gv8-vfvf-62f2, UBUNTU-CVE-2026-63874

## What is CVE-2026-63874?

CVE-2026-63874 is a high-severity vulnerability in Linux, published on 19 Jul 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:

net: mctp: usb: fix race between urb completion and rx_retry cancellation

It's possible that sequencing between setting ->stopped and cancelling
the rx_retry work (in ndo_stop) could leave us with an urb queued:

    T1: ndo_stop                  T2: rx_retry_work
    ------------                  ----------------
                                  LD: ->stopped => false
    ST: ->stopped <= true
    usb_kill_urb()
                                  mctp_usb_rx_queue()
                                    usb_submit_urb()
    cancel_delayed_work_sync()

That urb completion can then re-schedule rx_retry_work.

Strenghen the sequencing between the stop (preventing another requeue)
and the cancel by updating both atomically under a new rx lock. After
setting ->rx_stopped, and cancelling pending work, we know that the
requeue cannot occur, so all that's left is killing any pending urb.

## Which versions are affected by CVE-2026-63874?


## How do I fix CVE-2026-63874?

Apply the vendor's patch.

## Is CVE-2026-63874 being exploited?

There is no known exploitation of CVE-2026-63874 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-63874 and fix it if it is affected.

What it is: CVE-2026-63874 is a high-severity vulnerability in Linux, published on 19 Jul 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-2026-63874 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-2026-63874/ (Markdown: https://insights.sbomify.com/CVE-2026-63874/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63874
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63874
- OSV: https://osv.dev/vulnerability/CVE-2026-63874

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63874/
Summaries are generated and may contain mistakes; the official description above is the record.