# CVE-2026-98198: hwmon: (pwm-fan) Stop RPM timer before freeing tach data

> A use-after-free in the Linux kernel PWM fan driver allows local attackers to cause a system crash or potentially execute code during device unbinding.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Oct 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-106185, BELL-CVE-2026-98198, DEBIAN-CVE-2026-98198, GHSA-vr2q-55hv-76j4, UBUNTU-CVE-2026-98198

## What is CVE-2026-98198?

CVE-2026-98198 is an use after free vulnerability in Linux, published on 6 Oct 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:

hwmon: (pwm-fan) Stop RPM timer before freeing tach data

sample_timer() rearms the RPM timer and accesses the devm-managed
ctx->tachs and ctx->pulses_per_revolution arrays. The cleanup action
which stops the timer is registered before those arrays are allocated.

Since devres releases entries in reverse order, driver detach can free
the arrays before pwm_fan_cleanup() shuts down the timer. A timer expiry
in that window accesses the freed tach data.

With a KASAN kernel, a test-only kprobe delayed entry to
pwm_fan_cleanup() while normal sysfs unbind ran. Each of three runs
reported three four-byte reads and two four-byte writes in sample_timer()
after its backing devm allocations had been freed. The helper did not
invoke the timer callback, cleanup actions or free functions.

With the fix, three matching unbind runs completed without KASAN, BUG,
WARNING, Oops or panic. Instrumentation confirmed that timer retirement
completed before the first timer backing allocation was released.

Split timer retirement from the power cleanup and register its devres
action after the timer backing data and IRQ actions are installed. This
preserves the early power rollback action while ensuring the timer is
retired before its backing data is released. Use timer_shutdown_sync()
because the callback can rearm itself.

## Which versions are affected by CVE-2026-98198?


## How do I fix CVE-2026-98198?

Apply the vendor's patch.

## Is CVE-2026-98198 being exploited?

There is no known exploitation of CVE-2026-98198 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98198 and fix it if it is affected.

What it is: CVE-2026-98198 is an use after free vulnerability in Linux, published on 6 Oct 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-2026-98198 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-2026-98198/ (Markdown: https://insights.sbomify.com/CVE-2026-98198/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98198
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98198
- OSV: https://osv.dev/vulnerability/CVE-2026-98198

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98198/
Summaries are generated and may contain mistakes; the official description above is the record.