# CVE-2026-98653: KVM: s390: Fix _gaccess_shadow_fault()

> A flaw in Linux kernel KVM s390 allows a local attacker to cause a denial of service by triggering an error in nested guest memory shadowing.

- **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:** 18 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-98653, GHSA-v97x-654r-4f82, UBUNTU-CVE-2026-98653

## What is CVE-2026-98653?

CVE-2026-98653 is a denial of service vulnerability in Linux, published on 18 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:

KVM: s390: Fix _gaccess_shadow_fault()

In some circumstances, it is possible that the page of nested guest
memory that is being shadowed is not present at all in the parent guest
gmap. dat_entry_walk() will not find any leaf entry and return with
-ENOENT, which will erroneously be propagated all the way to userspace.

Fix by manually calling gmap_link() on the memory of the nested guest
that is being shadowed if the mapping was not already present.

## Which versions are affected by CVE-2026-98653?


## How do I fix CVE-2026-98653?

Apply the vendor's patch.

## Is CVE-2026-98653 being exploited?

There is no known exploitation of CVE-2026-98653 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98653 and fix it if it is affected.

What it is: CVE-2026-98653 is a denial of service vulnerability in Linux, published on 18 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-2026-98653 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-2026-98653/ (Markdown: https://insights.sbomify.com/CVE-2026-98653/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98653
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98653
- OSV: https://osv.dev/vulnerability/CVE-2026-98653

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98653/
Summaries are generated and may contain mistakes; the official description above is the record.