Cross-site Scripting (XSS) Affecting check-mk package, versions <1.2.6p12-1ubuntu0.16.04.1+esm1


Severity

Recommended
low

Based on Ubuntu security rating.

Threat Intelligence

EPSS
1.72% (75th percentile)

Do your applications use this vulnerable package?

In a few clicks we can analyze your entire application and see what components are vulnerable in your application, and suggest you quick fixes.

Test your applications
  • Snyk IDSNYK-UBUNTU1604-CHECKMK-1617844
  • published22 Mar 2026
  • disclosed26 Jul 2021

Introduced: 26 Jul 2021

CVE-2021-36563  (opens in a new tab)
CWE-79  (opens in a new tab)

How to fix?

Upgrade Ubuntu:16.04 check-mk to version 1.2.6p12-1ubuntu0.16.04.1+esm1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream check-mk package and not the check-mk package as distributed by Ubuntu. See How to fix? for Ubuntu:16.04 relevant fixed versions and status.

The CheckMK management web console (versions 1.5.0 to 2.0.0) does not sanitise user input in various parameters of the WATO module. This 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), the XSS payload will be triggered when the user accesses some specific sections of the application. In the same sense a very dangerous potential way would be when an attacker who has the monitor role (not administrator) manages to get a stored XSS to steal the secretAutomation (for the use of the API in administrator mode) and thus be able to create another administrator user who has high privileges on the CheckMK monitoring web console. Another way is that persistent XSS allows an attacker to modify the displayed content or change the victim's information. Successful exploitation requires access to the web management interface, either with valid credentials or with a hijacked session.

CVSS Base Scores

version 3.1