# CVE-2026-42490: domctl lock open to abuse

> Attackers can cause denial of service in Xen hypervisor by exploiting a lock fairness issue when XSM/Flask is enabled.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/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:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Jun 2026
- **Updated:** 18 Jun 2026
- **Also known as:** ALPINE-CVE-2026-42490, DEBIAN-CVE-2026-42490, GHSA-9xq7-8p44-p7p4, UBUNTU-CVE-2026-42490

## What is CVE-2026-42490?

CVE-2026-42490 is a medium-severity vulnerability in Xen, published on 18 Jun 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

[This CNA information record relates to multiple CVEs; the
text explains which aspects/vulnerabilities correspond to which CVE.]

To create and manage guests, domctl operations are used by the control
domain, a possible Xenstore domain, or by a domain controlling a
particular guest.  Some of these operations may not be executed in
parallel, so a system-wide lock is used.  The way that lock is acquired
is, however, not providing any fairness.  This is CVE-2026-42489.

Furthermore, with XSM/Flask in use, the lock acquire will, for some
operations, occur ahead of any permission checking.  This is
CVE-2026-42490.

Weakness: CWE-667 (Improper Locking)

## Which versions are affected by CVE-2026-42490?


## How do I fix CVE-2026-42490?

Apply the vendor's patch.

## Is CVE-2026-42490 being exploited?

There is no known exploitation of CVE-2026-42490 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-42490 and fix it if it is affected.

What it is: CVE-2026-42490 is a medium-severity vulnerability in Xen, published on 18 Jun 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-42490 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-2026-42490/ (Markdown: https://insights.sbomify.com/CVE-2026-42490/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-42490
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-42490
- OSV: https://osv.dev/vulnerability/CVE-2026-42490

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-42490/
Summaries are generated and may contain mistakes; the official description above is the record.