Is CVE-2021-40906 actively exploited?

No active exploitation of CVE-2021-40906 has been confirmed so far. Continue monitoring, as exploit status can change.

Can CVE-2021-40906 be exploited remotely?

Yes. CVE-2021-40906 is exploitable remotely over the network (CVSS attack vector: Network).

What is the CVSS score of CVE-2021-40906?

CVE-2021-40906 has a CVSS score of 6.1 (MEDIUM).

HOME VULNERABILITIESCVE-2021-40906

MEDIUM

CVE-2021-40906

CWE-79Published: March 25, 2022· Updated: Jul 9, 2026

6.1

CVSS v3.1

Official Description

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.

NVD Source

Technical Analysis

CVE-2021-40906 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

Exploitation does not require any privileges, though user interaction (Required) is needed, which slightly reduces the risk of mass automated attacks.

The vulnerability has a "Changed" scope, meaning successful exploitation can impact components beyond the vulnerable component itself — such as the host operating system or adjacent services.

From a weakness classification perspective (CWE-79): Cross-site scripting (XSS) vulnerabilities allow attackers to inject malicious scripts into web pages viewed by other users.