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CVE-2021-40906

CheckMK Raw Edition software (versions 1.5.0 to 1.6.0) does not sanitise the input of a web...

6.1 MediumPublic exploitFix available

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
Required

What an attacker can affect

Confidentiality
Low
Integrity
Low
Availability
None

Exploit likelihood

1.00%Down 0.4 points since Mar 26, 2022
90%50%10%1%

What each source reports

NVD Score used 6.1

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.

Record
CVE-2021-40906
CVSS 3.1
6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
CVSS 2.0
4.3 MediumAV:N/AC:M/Au:N/C:N/I:P/A:N
Weakness
CWE-79
Updated
2026-11-02
CVE List No score

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.

Record
CVE-2021-40906
Updated
2026-11-02
EUVDEUVD-2021-28061 No score

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.

Record
EUVD-2021-28061
Updated
2026-11-02
GitHub AdvisoriesGHSA-jv73-q4rg-p7qh 6.1

CheckMK Raw Edition software (versions 1.5.0 to 1.6.0) does not sanitise the input of a web...

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.

Record
GHSA-jv73-q4rg-p7qh
CVSS 3.1
6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Weakness
CWE-79
Updated
2026-11-02
OSV 6.1

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.

Record
CVE-2021-40906
CVSS 3.1
6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Updated
2026-11-02
OSVUBUNTU-CVE-2021-40906 6.1

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.

Record
UBUNTU-CVE-2021-40906
CVSS 3.1
6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Updated
2026-11-02
OSVUSN-5527-1 No score

check-mk vulnerabilities

It was discovered that Checkmk incorrectly handled authentication. An attacker could possibly use this issue to cause a race condition leading to information disclosure. (CVE-2017-14955)

It was discovered that Checkmk incorrectly handled certain inputs. An attacker could use these cross-site scripting issues to inject arbitrary html or javascript code to obtain sensitive information including user information, session cookies and valid credentials. (CVE-2017-9781, CVE-2021-36563, CVE-2021-40906, CVE-2022-24565)

Record
USN-5527-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
check-mk
Ubuntu:18.04:LTS
before 1.2.8p16-1ubuntu0.2, plus listed versions
1.2.8p16-1ubuntu0.1
1.2.8p16-1ubuntu0.2
check-mk
Ubuntu:18.04:LTS
From an advisory covering 5 CVEs
before 1.2.8p16-1ubuntu0.2, plus listed versions
1.2.8p16-1ubuntu0.1
1.2.8p16-1ubuntu0.2

Public exploits

Links only. Every CVE stores no exploit code.

Public exploits
SourceLinkDate
PoC in GitHubEdgarloyola/CVE-2021-409062021-10-12

History

History
RecordedChangedSources
affected, facts
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV, PoC in GitHub

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-40906 is a medium vulnerability (CVSS 6.1) in Checkmk, published March 25, 2022. Public exploit code exists. EPSS puts the chance of exploitation in the next 30 days at 1.00%, the 62nd percentile. Fixed in check-mk 1.2.8p16-1ubuntu0.2.

References

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