# CVE-2026-9549: Fix XSS in service discovery active check output

> Administrators can inject malicious scripts into service discovery check outputs, which execute in the browsers of other users viewing the page.

- **Severity:** Medium 4.8 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 8 Jun 2026
- **Updated:** 8 Jun 2026
- **Also known as:** GHSA-h7cw-jgmc-mwc6, UBUNTU-CVE-2026-9549

## What is CVE-2026-9549?

CVE-2026-9549 is a medium-severity cross-site scripting vulnerability in Checkmk Checkmk, published on 8 Jun 2026. An attacker needs administrator access to exploit it, and only if a user opens a file or follows a link.

### Official description

Stored cross-site scripting in the service discovery active check output in Checkmk <2.5.0p5, <2.4.0p31, <2.3.0p48, and all 2.2.0 versions allows an administrator who can configure active or custom checks to inject malicious HTML or JavaScript into check output that executes in the browser of an admin or a user with host read permissions when they run the check on the service discovery page.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2026-9549?

It affects 1 product.


Products: Checkmk Checkmk.

## How do I fix CVE-2026-9549?

No fix has been published for CVE-2026-9549 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-9549 being exploited?

There is no known exploitation of CVE-2026-9549 in the wild and no public exploit code.

## Other vulnerabilities in Checkmk Checkmk

- [CVE-2025-39666](https://insights.sbomify.com/CVE-2025-39666/): omd: Local privilege escalation when executing omd commands as root (critical 9.3)
- [CVE-2024-8606](https://insights.sbomify.com/CVE-2024-8606/): Fix 2FA bypass via RestAPI (critical 9.2)
- [CVE-2022-46836](https://insights.sbomify.com/CVE-2022-46836/): PHP code injection in watolib (critical 9.1)
- [CVE-2025-32919](https://insights.sbomify.com/CVE-2025-32919/): Privilege Escalation in Windows License plugin for Checkmk Windows Agent (high 8.8)
- [CVE-2024-28827](https://insights.sbomify.com/CVE-2024-28827/): Privilege escalation in Windows agent (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-9549 and fix it if it is affected.

What it is: CVE-2026-9549 is a medium-severity cross-site scripting vulnerability in Checkmk Checkmk, published on 8 Jun 2026. An attacker needs administrator access to exploit it, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-9549 in the wild and no public exploit code.

Affected product: Checkmk Checkmk. 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-2026-9549/ (Markdown: https://insights.sbomify.com/CVE-2026-9549/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-9549
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-9549
- OSV: https://osv.dev/vulnerability/CVE-2026-9549

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-9549/
Summaries are generated and may contain mistakes; the official description above is the record.