CVE-2021-40906Public exploitNetwork attack vector

Session theft via unsanitized reflected web parameter

Published Mar 25, 2022 · Updated Jul 9, 2026

Reflected XSS in CheckMK Raw Edition 1.5.0 through 1.6.0 allows remote attackers to run script in a user's browser via a crafted URL. The pnp_template.py web service reflects an unsanitized request parameter into the returned page, causing the browser to interpret attacker-supplied HTML or JavaScript. The endpoint requires no authentication, but a previously authenticated user must open the crafted URL; execution can expose that user's session cookie or alter page content.

CVSS severity6.1
Medium
EPSS probability0.99%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Reflected XSS in CheckMK Raw Edition 1.5.0 through 1.6.0 allows remote attackers to run script in a user's browser via a crafted URL. The pnp_template.py web service reflects an unsanitized request parameter into the returned page, causing the browser to interpret attacker-supplied HTML or JavaScript. The endpoint requires no authentication, but a previously authenticated user must open the crafted URL; execution can expose that user's session cookie or alter page content.

The record

CVE
CVE-2021-40906
Published
Mar 25, 2022
Updated
Jul 9, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 25, 2022CVE publishedPublication date reported by the CVE source.
  2. Jul 9, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1059.007Command and Scripting Interpreter: JavaScript

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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