# CVE-2026-90004: mm/damon/core: handle region split failure in apply_min_nr_regions()

> A null pointer dereference in the Linux kernel DAMON subsystem can cause memory corruption or crashes when region splitting fails due to allocation errors.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Not stated
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-90004, GHSA-fxh6-hh4r-jg4j, UBUNTU-CVE-2026-90004

## What is CVE-2026-90004?

CVE-2026-90004 is a vulnerability in Linux, published on 16 Sep 2026. 

### Official description

In the Linux kernel, the following vulnerability has been resolved:

mm/damon/core: handle region split failure in apply_min_nr_regions()

damon_apply_min_nr_regions() repeatedly split each region until its size
becomes small enough to meet the user-defined low limit of the number of
regions.  The loop assumes the split operation (damon_split_region_at())
will always succeed and create the new region.  But the operation could
silently fail for memory allocation failures, for example.

If such failure happens and the region was the last region, the linked
list-based next region fetching returns invalid pointer.  As a result,
invalid memory dereference and corruption could happen.  Even if the
corner case is handled, it imposes stress to the allocator by trying split
regions for other targets.  Fix the issue by breaking all the loops for
any region split failure.

This means there could be a min_nr_regions violation.  It will only rarely
happen since the allocation is arguably too small to fail.  Even if it
happens, it is only temporal.  damon_apply_min_nr_regions() will be called
again after the aggregation interval.

The user impact of the issue should be minor, since the allocation is
arguably too small to fail.  But, it could still theoretically happen, and
the consequence is very bad.

This issue was discovered [1] by Sashiko.

## Which versions are affected by CVE-2026-90004?


## How do I fix CVE-2026-90004?

Apply the vendor's patch.

## Is CVE-2026-90004 being exploited?

There is no known exploitation of CVE-2026-90004 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90004 and fix it if it is affected.

What it is: CVE-2026-90004 is a vulnerability in Linux, published on 16 Sep 2026. 
Exploitation: There is no known exploitation of CVE-2026-90004 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-2026-90004/ (Markdown: https://insights.sbomify.com/CVE-2026-90004/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90004
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90004
- OSV: https://osv.dev/vulnerability/CVE-2026-90004

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90004/
Summaries are generated and may contain mistakes; the official description above is the record.