# CVE-2026-23557: Xenstored DoS via XS_RESET_WATCHES command

> A guest can crash the Xen hypervisor's xenstored service by sending a specific command, causing a denial of service.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/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:** 19 May 2026
- **Updated:** 19 May 2026
- **Also known as:** ALPINE-CVE-2026-23557, DEBIAN-CVE-2026-23557, GHSA-9879-vj7m-r497, UBUNTU-CVE-2026-23557

## What is CVE-2026-23557?

CVE-2026-23557 is a medium-severity denial of service vulnerability in Xen Xen, published on 19 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Any guest can cause xenstored to crash by issuing a XS_RESET_WATCHES
command within a transaction due to an assert() triggering.

In case xenstored was built with NDEBUG #defined nothing bad will
happen, as assert() is doing nothing in this case. Note that the
default is not to define NDEBUG for xenstored builds even in release
builds of Xen.

Weakness: CWE-617 (Reachable Assertion)

## Which versions are affected by CVE-2026-23557?

It affects 1 product.


Products: Xen Xen.

## How do I fix CVE-2026-23557?

Apply the vendor's patch.

## Is CVE-2026-23557 being exploited?

There is no known exploitation of CVE-2026-23557 in the wild and no public exploit code.

## Other vulnerabilities in Xen Xen

- [CVE-2017-10912](https://insights.sbomify.com/CVE-2017-10912/): Privilege escalation in n/a (critical 10.0)
- [CVE-2017-10918](https://insights.sbomify.com/CVE-2017-10918/): Memory corruption in n/a (critical 10.0)
- [CVE-2017-10920](https://insights.sbomify.com/CVE-2017-10920/): Memory corruption in n/a (critical 10.0)
- [CVE-2017-10921](https://insights.sbomify.com/CVE-2017-10921/): Memory corruption in n/a (critical 10.0)
- [CVE-2025-27466](https://insights.sbomify.com/CVE-2025-27466/): Mutiple vulnerabilities in the Viridian interface (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-23557 and fix it if it is affected.

What it is: CVE-2026-23557 is a medium-severity denial of service vulnerability in Xen Xen, published on 19 May 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-2026-23557 in the wild and no public exploit code.

Affected product: Xen 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-2026-23557/ (Markdown: https://insights.sbomify.com/CVE-2026-23557/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23557
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23557
- OSV: https://osv.dev/vulnerability/CVE-2026-23557

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-23557/
Summaries are generated and may contain mistakes; the official description above is the record.