CVE-2021-40906

mediumpriority · track · 34EPSS 0.010 · 62 %ileexploit · PoCEUUS

grimoire priorityP1 · Urgent

Exploitable?

Public exploit

1 exploit · PoC

Likely / severe?

0.99% (62nd) EPSS

CVSS 4.3 · medium

Is it mine?

8 products

Check your exposure

Who says so?

3 sources

cnnvd · enisa_euvd · nvd

EPSS · scored 2026-10-27

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.

cvss

Technical severity, 0–10. One row per scoring source.

6.1

010

base score 0–10 · higher = more severe · hover a vector to decode

v2.04.3mediumAV:N/AC:M/Au:N/C:N/I:P/A:Nprimary · NVD / NIST USexploitability 8.6 · impact 2.9

v3.16.1mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:Nprimary · NVD / NIST USexploitability 2.8 · impact 2.7

v3.15.8mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N/E:Psecondary · CVSS-BT (t0sche)

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-79USprimary

exploits (1)

Public proof-of-concept and weaponised exploit code.

Edgarloyola/CVE-2021-40906Edgarloyola/CVE-2021-40906PoC · poc_in_github

affected products (8)

Products and version ranges known to be affected.

n/a n/a≤ n/aenisa_euvdEU
checkmk checkmk1.5.0 → 1.6.0nvdUScpe:2.3:a:checkmk:checkmk:*:*:*:*:*:*:*:*
checkmk checkmk= 1.6.0nvdUScpe:2.3:a:checkmk:checkmk:*:*:*:*:*:*:*:*
tribe29 checkmk= 1.6.0b10nvdUScpe:2.3:a:tribe29:checkmk:*:*:*:*:*:*:*:*
tribe29 checkmk= 1.6.0b11nvdUScpe:2.3:a:tribe29:checkmk:*:*:*:*:*:*:*:*
tribe29 checkmk= 1.6.0p10nvdUScpe:2.3:a:tribe29:checkmk:*:*:*:*:*:*:*:*
tribe29 checkmk= 1.6.0p17nvdUScpe:2.3:a:tribe29:checkmk:*:*:*:*:*:*:*:*
tribe29 checkmk= 1.6.0p18nvdUScpe:2.3:a:tribe29:checkmk:*:*:*:*:*:*:*:*

also known as (3)

Other names and identifiers for this entity.

sources

Which sources assert this record, and when.

cnnvd enisa_euvd nvd NVD CVE.org MITRE

published 2022-03-25modified 2026-07-09

related (53,013)

Related entries.

ID	severity	EPSS	exploitable	published
CVE-2026-42897US	medium6.1OT critical	70.7% (99th)	KEV	2026-05-14
Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Exchange Server allows an unauthorized attacker to perform spoofing over a network…
CVE-2025-66376US	medium6.1OT critical	20.2% (97th)	KEV	2026-01-05
Zimbra Collaboration (ZCS) 10 before 10.0.18 and 10.1 before 10.1.13 allows Classic UI stored XSS via Cascading Style Sheets (CSS) @import directives in an HTML e-mail message.
CVE-2025-68461US	medium6.1OT critical	27.4% (98th)	KEV	2025-12-18
Roundcube Webmail before 1.5.12 and 1.6 before 1.6.12 is prone to a Cross-Site-Scripting (XSS) vulnerability via the animate tag in an SVG document.
CVE-2025-48700US	—OT critical	1.71% (77th)	KEV	2025-06-23
An issue was discovered in Zimbra Collaboration (ZCS) 8.8.15 and 9.0 and 10.0 and 10.1. A Cross-Site Scripting (XSS) vulnerability in the Zimbra Classic UI allows attackers to exec…
CVE-2025-27915US	—OT critical	4.06% (91st)	KEV	2025-03-12
An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0 and 10.1. A stored cross-site scripting (XSS) vulnerability exists in the Classic Web Client due to insufficient…

+53008 more

references (9)

External citations — patches, advisories, analysis.

scry

Attackers weaponise vulnerabilities like this against internet-exposed services. See what is exposed on your perimeter with a free passive scan.

Free scan