# CVE-2026-31740: counter: rz-mtu3-cnt: do not use struct rz_mtu3_channel's dev member

> A race condition in the Linux kernel counter driver causes incorrect device pointer assignment, potentially leading to runtime power management errors and system instability.

- **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:** 1 May 2026
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2026-31740, DEBIAN-CVE-2026-31740, GHSA-7cjr-2c82-2wh7, ROOT-OS-UBUNTU-2404-CVE-2026-31740, UBUNTU-CVE-2026-31740

## What is CVE-2026-31740?

CVE-2026-31740 is a medium-severity vulnerability in Linux kernel, published on 1 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:

counter: rz-mtu3-cnt: do not use struct rz_mtu3_channel's dev member

The counter driver can use HW channels 1 and 2, while the PWM driver can
use HW channels 0, 1, 2, 3, 4, 6, 7.

The dev member is assigned both by the counter driver and the PWM driver
for channels 1 and 2, to their own struct device instance, overwriting
the previous value.

The sub-drivers race to assign their own struct device pointer to the
same struct rz_mtu3_channel's dev member.

The dev member of struct rz_mtu3_channel is used by the counter
sub-driver for runtime PM.

Depending on the probe order of the counter and PWM sub-drivers, the
dev member may point to the wrong struct device instance, causing the
counter sub-driver to do runtime PM actions on the wrong device.

To fix this, use the parent pointer of the counter, which is assigned
during probe to the correct struct device, not the struct device pointer
inside the shared struct rz_mtu3_channel.

## Which versions are affected by CVE-2026-31740?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31740?

Apply the vendor's patch.

## Is CVE-2026-31740 being exploited?

There is no known exploitation of CVE-2026-31740 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-2026-31740 and fix it if it is affected.

What it is: CVE-2026-31740 is a medium-severity vulnerability in Linux kernel, published on 1 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-2026-31740 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-2026-31740/ (Markdown: https://insights.sbomify.com/CVE-2026-31740/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31740
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31740
- OSV: https://osv.dev/vulnerability/CVE-2026-31740

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31740/
Summaries are generated and may contain mistakes; the official description above is the record.