# CVE-2025-64999: Cross-site scripting in HTML logs of Synthetic Monitoring test services

> Attackers can inject malicious JavaScript into Synthetic Monitoring HTML logs via manipulated check output, potentially leading to code execution or account takeover.

- **Severity:** High 7.3 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:A/VC:H/VI:H/VA:H/SC:N/SI:L/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 26 Feb 2026
- **Updated:** 14 Apr 2026
- **Also known as:** GHSA-p5q4-qc3r-2w36, UBUNTU-CVE-2025-64999

## What is CVE-2025-64999?

CVE-2025-64999 is a high-severity cross-site scripting vulnerability in Checkmk Checkmk, published on 26 Feb 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

Improper neutralization of input in Checkmk versions 2.4.0 before 2.4.0p22, and 2.3.0 before 2.3.0p43 allows an attacker that can manipulate a host's check output to inject malicious JavaScript into the Synthetic Monitoring HTML logs, which can then be accessed via a crafted phishing link.

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

## Which versions are affected by CVE-2025-64999?

It affects 1 product.


Products: Checkmk Checkmk.

## How do I fix CVE-2025-64999?

No fix has been published for CVE-2025-64999 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-64999 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-64999 exists.

## 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-2025-64999 and fix it if it is affected.

What it is: CVE-2025-64999 is a high-severity cross-site scripting vulnerability in Checkmk Checkmk, published on 26 Feb 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-64999 exists.

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-2025-64999/ (Markdown: https://insights.sbomify.com/CVE-2025-64999/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-64999
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-64999
- OSV: https://osv.dev/vulnerability/CVE-2025-64999

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-64999/
Summaries are generated and may contain mistakes; the official description above is the record.