# CVE-2026-98286: drop_monitor: use timer_shutdown_sync() to prevent timer rearming during teardown

> A race condition in the Linux kernel drop_monitor module allows a use-after-free leading to kernel panic or code execution during teardown.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-106047, BELL-CVE-2026-98286, DEBIAN-CVE-2026-98286, GHSA-g656-78v2-2243, UBUNTU-CVE-2026-98286

## What is CVE-2026-98286?

CVE-2026-98286 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:

drop_monitor: use timer_shutdown_sync() to prevent timer rearming during teardown

In drop_monitor teardown paths (net_dm_trace_off_set(),
net_dm_hw_monitor_stop(), and error unwind paths in net_dm_trace_on_set()
and net_dm_hw_monitor_start()), per-CPU timers are stopped using
timer_delete_sync() followed by cancel_work_sync().

However, there is a circular dependency between send_timer and
dm_alert_work:
1) sched_send_work() (timer callback) schedules dm_alert_work.
2) send_dm_alert() / net_dm_hw_summary_work() calls reset_per_cpu_data()
   or net_dm_hw_reset_per_cpu_data().
3) If memory allocation fails under memory pressure in the reset
   function, it re-arms the timer via mod_timer(&data->send_timer, ...).

If dm_alert_work is running concurrently while timer_delete_sync()
executes on another CPU, an allocation failure in the worker will
re-arm the timer after timer_delete_sync() has already returned.
Once cancel_work_sync() completes and module_put() is called, the timer
remains active in the timer wheel. If the module is then unloaded, the
timer will fire and execute sched_send_work() in freed memory,
triggering a kernel panic / use-after-free.

Switch from timer_delete_sync() to timer_shutdown_sync(). This guarantees
that any in-flight timer handler has finished and prevents subsequent
re-arming attempts from running workers from succeeding. When monitoring
is restarted later, timer_setup() is invoked, which cleanly
re-initializes the timer.

## Which versions are affected by CVE-2026-98286?


## How do I fix CVE-2026-98286?

Apply the vendor's patch.

## Is CVE-2026-98286 being exploited?

There is no known exploitation of CVE-2026-98286 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98286 and fix it if it is affected.

What it is: CVE-2026-98286 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-2026-98286 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-2026-98286/ (Markdown: https://insights.sbomify.com/CVE-2026-98286/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98286
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98286
- OSV: https://osv.dev/vulnerability/CVE-2026-98286

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98286/
Summaries are generated and may contain mistakes; the official description above is the record.