# CVE-2026-63942: parport: Fix race between port and client registration

> A race condition in the Linux kernel parport subsystem allows client drivers to attach to uninitialized ports, potentially causing a system crash.

- **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:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-63942, DEBIAN-CVE-2026-63942, GHSA-g8r4-rq83-8vj2, ROOT-OS-UBUNTU-2204-CVE-2026-63942, UBUNTU-CVE-2026-63942

## What is CVE-2026-63942?

CVE-2026-63942 is a high-severity vulnerability in Linux kernel, 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:

parport: Fix race between port and client registration

The parport subsystem registers port devices before they are fully
initialised, resulting in a race condition where client drivers such
as lp can attach to ports that are not completely initialised or even
being torn down.

When the port and client drivers are built as modules and loaded
around the same time during boot, this occasionally results in a
crash.  I was able to make this happen reliably in a VM with a
PC-style parallel port by patching parport_pc to fail probing:

> --- a/drivers/parport/parport_pc.c
> +++ b/drivers/parport/parport_pc.c
> @@ -2069,7 +2069,7 @@ static struct parport *__parport_pc_probe_port(unsigned long int base,
>  	if (!p)
>  		goto out3;
>
> -	base_res = request_region(base, 3, p->name);
> +	base_res = NULL;
>  	if (!base_res)
>  		goto out4;
>

and then running:

    while true; do
        modprobe lp & modprobe parport_pc
	wait
	rmmod lp parport_pc
    done

for a few seconds.

In the long term I think port registration should be changed to put
the call to device_add() inside parport_announce_port(), but since the
latter currently cannot fail this will require changing all port
drivers.

For now, add a flag to indicate whether a port has been "announced"
and only try to attach client drivers to ports when the flag is set.

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2026-63942?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-63942?

Apply the vendor's patch.

## Is CVE-2026-63942 being exploited?

There is no known exploitation of CVE-2026-63942 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-2026-63942 and fix it if it is affected.

What it is: CVE-2026-63942 is a high-severity vulnerability in Linux kernel, 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-2026-63942 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-2026-63942/ (Markdown: https://insights.sbomify.com/CVE-2026-63942/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63942
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63942
- OSV: https://osv.dev/vulnerability/CVE-2026-63942

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63942/
Summaries are generated and may contain mistakes; the official description above is the record.