# CVE-2026-79611: VMX: VMentry failure with branch tracing and blocked states

> A guest VM can cause a fatal VMEntry failure and crash itself by triggering a specific state combination involving branch tracing and blocked states.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 13 Oct 2026
- **Updated:** 20 Oct 2026
- **Also known as:** ALPINE-CVE-2026-79611, DEBIAN-CVE-2026-79611, GHSA-28w8-qvww-f539, UBUNTU-CVE-2026-79611

## What is CVE-2026-79611?

CVE-2026-79611 is a medium-severity denial of service vulnerability in Xen, published on 13 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

For XSA-308 logic was introduced, as VMX VMEntry checks do not like the
exact combination of state which occurs when #DB in intercepted, Single
Stepping is active, and blocked by STI/MovSS is active, despite this being
a legitimate state to be in.  The resulting VMEntry failure is fatal to
the guest.

Sadly there is another special sub-case of the above, with branch tracing
enabled.  In that case the prior adjustment would still cause a VMentry
failure, as before fatal to the guest.

Weakness: CWE-843 (Access of Resource Using Incompatible Type)

## Which versions are affected by CVE-2026-79611?


## How do I fix CVE-2026-79611?

Apply the vendor's patch.

## Is CVE-2026-79611 being exploited?

There is no known exploitation of CVE-2026-79611 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-79611 and fix it if it is affected.

What it is: CVE-2026-79611 is a medium-severity denial of service vulnerability in Xen, published on 13 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-2026-79611 in the wild and no public exploit code.

Affected product: Xen. 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-2026-79611/ (Markdown: https://insights.sbomify.com/CVE-2026-79611/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-79611
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-79611
- OSV: https://osv.dev/vulnerability/CVE-2026-79611

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-79611/
Summaries are generated and may contain mistakes; the official description above is the record.