CVE-2021-40906

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.

Published: 2022-03-25 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-40906 is rated Moderate Risk (45/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 0.99%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-40906

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.62% 0.99% +0.36%
2 2026-02-03 0.84% 0.62% -0.22%
3 2025-11-21 — 0.84% —

Full EPSS history (19 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-40906

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.1 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 2.8 2.7 [email protected]
4.3 2.0 MEDIUM
AV:N/AC:M/Au:N/C:N/I:P/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
 8.6 2.9 [email protected]

Weakness enumeration for CVE-2021-40906

OS Trackers for CVE-2021-40906

vendor priority summary link
ubuntu medium CVE-2021-40906 medium priority: Ubuntu including 1 source packages (check-mk), 6 status rows across 6 suites (bionic, focal, jammy, trusty, upstream, xenial): DNE 2, released 2, ignored 1, not-affected 1. https://ubuntu.com/security/CVE-2021-40906

Affected software / configurations for CVE-2021-40906

Vendor Product Version Raw CPE
checkmk checkmk >= 1.5.0, < 1.6.0 cpe:2.3:a:checkmk:checkmk:*:*:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:-:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:b1:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:b10:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:b12:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:b3:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:b4:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:b5:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:b9:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p1:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p10:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p11:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p12:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p13:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p14:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p15:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p16:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p19:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p2:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p20:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p21:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p22:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p23:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p24:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p25:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p3:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p4:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p5:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p6:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p7:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p8:*:*:*:*:*:*
checkmk checkmk 1.6.0 cpe:2.3:a:checkmk:checkmk:1.6.0:p9:*:*:*:*:*:*
tribe29 checkmk 1.6.0b10 cpe:2.3:a:tribe29:checkmk:1.6.0b10:*:*:*:*:*:*:*
tribe29 checkmk 1.6.0b11 cpe:2.3:a:tribe29:checkmk:1.6.0b11:*:*:*:*:*:*:*
tribe29 checkmk 1.6.0p10 cpe:2.3:a:tribe29:checkmk:1.6.0p10:*:*:*:*:*:*:*
tribe29 checkmk 1.6.0p17 cpe:2.3:a:tribe29:checkmk:1.6.0p17:*:*:*:*:*:*:*
tribe29 checkmk 1.6.0p18 cpe:2.3:a:tribe29:checkmk:1.6.0p18:*:*:*:*:*:*:*

References for CVE-2021-40906

cvelogic Threat Intelligence