# CVE-2026-89593: hugetlb: only adjust reservation during unmapping if mapcount is 0

> A logic error in Linux kernel hugetlb unmapping causes reservation count underflow, potentially leading to denial of service.

- **Severity:** High 7.1 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/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:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-89593, DEBIAN-CVE-2026-89593, GHSA-xm38-wfrw-x5q7, UBUNTU-CVE-2026-89593

## What is CVE-2026-89593?

CVE-2026-89593 is a high-severity vulnerability in Linux, published on 11 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:

hugetlb: only adjust reservation during unmapping if mapcount is 0

Since df7a6d1f6405, __unmap_hugepage_range can adjust reservations.  In
the case of folio mapped in both a parent and a child, if the parent
unmaps the range first, the reservation adjustment will result in an
underflow of the reserved count.  Once the child unmaps the range, the
count is restored.  Change __unmap_hugepage_range() to check the mapcount
before adjusting the reservation.

## Which versions are affected by CVE-2026-89593?


## How do I fix CVE-2026-89593?

Apply the vendor's patch.

## Is CVE-2026-89593 being exploited?

There is no known exploitation of CVE-2026-89593 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89593 and fix it if it is affected.

What it is: CVE-2026-89593 is a high-severity vulnerability in Linux, published on 11 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-2026-89593 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-2026-89593/ (Markdown: https://insights.sbomify.com/CVE-2026-89593/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89593
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89593
- OSV: https://osv.dev/vulnerability/CVE-2026-89593

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89593/
Summaries are generated and may contain mistakes; the official description above is the record.