# CVE-2026-90006: samples/damon/mtier: handle damon_stop() failure

> A use-after-free vulnerability in the Linux kernel DAMON mtier sample allows local attackers to execute arbitrary code or escalate privileges.

- **Severity:** Not scored
- **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:** 16 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-90006, DEBIAN-CVE-2026-90006, GHSA-vfcg-xg68-fq77, UBUNTU-CVE-2026-90006

## What is CVE-2026-90006?

CVE-2026-90006 is an use after free vulnerability in Linux, published on 16 Sep 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:

samples/damon/mtier: handle damon_stop() failure

damon_sample_mtier_stop() assumes its damon_stop() call will always
successfully stops the two DAMON contexts.  Hence it deallocates the two
DAMON contexts after the damon_stop() call.  However, if a given context
is already stopped, damon_stop() fails and returns an error while letting
the DAMON contexts that have not yet stopped keep running.  This kind of
unexpected early DAMON context stops could happen due to memory allocation
failures in kdamond_fn().  Because damon_sample_mtier_stop() just
deallocates all DAMON contexts with damon_target and damon_region objects
that are linked to the contexts, the execution of the unstopped DAMON
context (kdamond) ends up using the memory that freed (use-after-free). 
Fix the issue by separating the damon_stop() to be invoked per context.

Note that DAMON_SYSFS also allows multiple DAMON contexts execution.  But,
it calls damon_stop() for each context one by one.  Hence this issue is
only in mtier.

For the long term, it would be better to refactor damon_stop() to always
ensure stopping all contexts regardless of the failures in the middle. 
Make this fix in the current way, though, to keep it simple and easy to
backport.  I will do the refactoring later.

The issue was discovered [1] by Sashiko.

## Which versions are affected by CVE-2026-90006?


## How do I fix CVE-2026-90006?

Apply the vendor's patch.

## Is CVE-2026-90006 being exploited?

There is no known exploitation of CVE-2026-90006 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90006 and fix it if it is affected.

What it is: CVE-2026-90006 is an use after free vulnerability in Linux, published on 16 Sep 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-2026-90006 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-2026-90006/ (Markdown: https://insights.sbomify.com/CVE-2026-90006/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90006
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90006
- OSV: https://osv.dev/vulnerability/CVE-2026-90006

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90006/
Summaries are generated and may contain mistakes; the official description above is the record.