# CVE-2025-38217: hwmon: (ftsteutates) Fix TOCTOU race in fts_read()

> A race condition in the Linux kernel hwmon driver allows a local attacker to trigger a crash or undefined behavior via concurrent access to fan source data.

- **Severity:** Medium 4.7 (`CVSS:3.1/AV:L/AC:H/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:** 4 Jul 2025
- **Updated:** 11 May 2026
- **Also known as:** AZL-64707, BELL-CVE-2025-38217, DEBIAN-CVE-2025-38217, GHSA-gcgx-pvvc-73xm, ROOT-OS-UBUNTU-2404-CVE-2025-38217, UBUNTU-CVE-2025-38217

## What is CVE-2025-38217?

CVE-2025-38217 is a medium-severity vulnerability in Linux kernel, published on 4 Jul 2025. 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:

hwmon: (ftsteutates) Fix TOCTOU race in fts_read()

In the fts_read() function, when handling hwmon_pwm_auto_channels_temp,
the code accesses the shared variable data->fan_source[channel] twice
without holding any locks. It is first checked against
FTS_FAN_SOURCE_INVALID, and if the check passes, it is read again
when used as an argument to the BIT() macro.

This creates a Time-of-Check to Time-of-Use (TOCTOU) race condition.
Another thread executing fts_update_device() can modify the value of
data->fan_source[channel] between the check and its use. If the value
is changed to FTS_FAN_SOURCE_INVALID (0xff) during this window, the
BIT() macro will be called with a large shift value (BIT(255)).
A bit shift by a value greater than or equal to the type width is
undefined behavior and can lead to a crash or incorrect values being
returned to userspace.

Fix this by reading data->fan_source[channel] into a local variable
once, eliminating the race condition. Additionally, add a bounds check
to ensure the value is less than BITS_PER_LONG before passing it to
the BIT() macro, making the code more robust against undefined behavior.

This possible bug was found by an experimental static analysis tool
developed by our team.

Weakness: CWE-367 (Time-of-check Time-of-use (TOCTOU) Race Condition)

## Which versions are affected by CVE-2025-38217?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-38217?

Apply the vendor's patch.

## Is CVE-2025-38217 being exploited?

There is no known exploitation of CVE-2025-38217 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-2025-38217 and fix it if it is affected.

What it is: CVE-2025-38217 is a medium-severity vulnerability in Linux kernel, published on 4 Jul 2025. 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-2025-38217 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-2025-38217/ (Markdown: https://insights.sbomify.com/CVE-2025-38217/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-38217
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-38217
- OSV: https://osv.dev/vulnerability/CVE-2025-38217

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-38217/
Summaries are generated and may contain mistakes; the official description above is the record.