CVE-2025-39663Public exploitNetwork attack vectorHinoki check available

Session takeover via unescaped remote service output

Published Oct 30, 2025 · Updated Oct 30, 2025

Stored XSS in Checkmk before 2.4.0p14 and 2.3.0p39 allows remote authenticated users to execute JavaScript via service output. The central site renders HTML supplied in a connected remote site's service summary or details without escaping it when that site permits raw output. A compromised connected remote site and a user viewing its host or service page are required; the script inherits that user's web session, and an administrator session enables server command execution.

CVSS severity8.5
High
EPSS probability0.56%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Stored XSS in Checkmk before 2.4.0p14 and 2.3.0p39 allows remote authenticated users to execute JavaScript via service output. The central site renders HTML supplied in a connected remote site's service summary or details without escaping it when that site permits raw output. A compromised connected remote site and a user viewing its host or service page are required; the script inherits that user's web session, and an administrator session enables server command execution.

The record

CVE
CVE-2025-39663
Published
Oct 30, 2025
Updated
Oct 30, 2025
Vendor
Checkmk GmbH
Product
Checkmk
Classifications
CWE-80, CWE-79, T1059.007
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Oct 30, 2025CVE publishedPublication date reported by the CVE source.
  2. Oct 30, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2.1.0
  2. Affected versionversion=2.2.0
  3. Affected versionversion=2.3.0 <2.3.0p39
  4. Affected versionversion=2.4.0 <2.4.0p14

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Checkmk GmbH · Checkmkversion=2.1.0; version=2.2.0; version=2.3.0 <2.3.0p39; version=2.4.0 <2.4.0p14

Published CVSS scores

8.4NVDCVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:H/I:H/A:H
9.1SBA ResearchCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H
8.5Checkmk GmbHCVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA: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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-80Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)
CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1059.007JavaScript/JScript

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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