CVE-2021-40906: Checkmk

Medium severity, CVSS 6.1. EPSS: 1% chance of exploitation in the next 30 days.

CheckMK Raw Edition software (versions 1.5.0 to 1.6.0) does not sanitise the input of a web service parameter that is in an unauthenticated zone. This Reflected XSS allows an attacker to open a backdoor on the device with HTML content and interpreted by the browser (such as JavaScript or other client-side scripts) or to steal the session cookies of a user who has previously authenticated via a man in the middle. Successful exploitation requires access to the web service resource without authentication.

Affected products

• Checkmk Checkmk: from 1.5.0, before 1.6.0 (fixed in 1.6.0); version 1.6.0 only
• TRIBE29 Checkmk: version 1.6.0b10 only; version 1.6.0b11 only; version 1.6.0p10 only; version 1.6.0p17 only; version 1.6.0p18 only

Published 2022-03-25. Last modified 2026-07-09.