CVE-2026-20915 Stored cross-site scripting in Pending Changes sidebar
Authenticated users can inject malicious JavaScript into the Pending Changes sidebar, executing code in other users' browsers.
- 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
- None listed
What is CVE-2026-20915?
CVE-2026-20915 is a high-severity cross-site scripting vulnerability in Checkmk Checkmk, published on 31 Mar 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 (XSS) in Checkmk version 2.5.0 (beta) before 2.5.0b2 allows authenticated users with permission to create pending changes to inject malicious JavaScript into the Pending Changes sidebar, which will execute in the browsers of other users viewing the sidebar.
Weakness: CWE-79
Which versions are affected by CVE-2026-20915?
It affects 1 product.
Products include Checkmk Checkmk.
How do I fix CVE-2026-20915?
No fix has been published for CVE-2026-20915 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-2026-20915 being exploited?
There is no known exploitation of CVE-2026-20915 in the wild and no public exploit code.
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-c37f-qch7-r2cg, UBUNTU-CVE-2026-20915.