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.
- 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
- None listed
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
Which versions are affected by CVE-2025-64999?
It affects 1 product.
Products include 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.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
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 omd: Local privilege escalation when executing omd commands as root
- CVE-2024-8606 Fix 2FA bypass via RestAPI
- CVE-2022-46836 PHP code injection in watolib
- CVE-2025-32919 Privilege Escalation in Windows License plugin for Checkmk Windows Agent
- CVE-2024-28827 Privilege escalation in Windows agent
Sources
Also known as GHSA-p5q4-qc3r-2w36, UBUNTU-CVE-2025-64999.