Checkmk up to 2.3.0p42/2.4.0p21 Synthetic Monitoring HTML Log HTML injection

CVSS Meta Temp Score
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CTI Interest Score
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4.4$0-$5k0.00

Summaryinfo

A vulnerability was found in Checkmk up to 2.3.0p42/2.4.0p21. It has been rated as problematic. This vulnerability affects unknown code of the component Synthetic Monitoring HTML Log. This manipulation causes HTML injection. This vulnerability is tracked as CVE-2025-64999. The attack is possible to be carried out remotely. No exploit exists. Upgrading the affected component is advised.

Detailsinfo

A vulnerability classified as problematic was found in Checkmk up to 2.3.0p42/2.4.0p21. Affected by this vulnerability is an unknown function of the component Synthetic Monitoring HTML Log. The manipulation with an unknown input leads to a html injection vulnerability. The CWE definition for the vulnerability is CWE-79. The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. As an impact it is known to affect integrity. The summary by CVE is:

Improper neutralization of input in Checkmk versions 2.4.0 before 2.4.0p22, and 2.3.0 before 2.3.0p43 allows an attacker that can manipulate a host's check output to inject malicious JavaScript into the Synthetic Monitoring HTML logs, which can then be accessed via a crafted phishing link.

The advisory is shared at checkmk.com. This vulnerability is known as CVE-2025-64999 since 11/12/2025. The exploitation appears to be easy. The attack can be launched remotely. It demands that the victim is doing some kind of user interaction. Neither technical details nor an exploit are publicly available. MITRE ATT&CK project uses the attack technique T1059.007 for this issue.

The vulnerability scanner Nessus provides a plugin with the ID 300827 (Linux Distros Unpatched Vulnerability : CVE-2025-64999), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 2.3.0p43 or 2.4.0p22 eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (300827) and CERT Bund (WID-SEC-2026-0543). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Affected

  • Checkmk Checkmk

Productinfo

Name

Version

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA CVSS-B Score: 🔒
CNA CVSS-BT Score: 🔒
CNA Vector: 🔒

CVSSv3info

VulDB Meta Base Score: 4.4
VulDB Meta Temp Score: 4.4

VulDB Base Score: 3.5
VulDB Temp Score: 3.4
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 5.4
NVD Vector: 🔒

CVSSv2info

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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: HTML injection
CWE: CWE-79 / CWE-94 / CWE-74
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 300827
Nessus Name: Linux Distros Unpatched Vulnerability : CVE-2025-64999

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Checkmk 2.3.0p43/2.4.0p22

Timelineinfo

11/12/2025 CVE reserved
02/26/2026 +106 days Advisory disclosed
02/26/2026 +0 days VulDB entry created
03/06/2026 +7 days VulDB entry last update

Sourcesinfo

Advisory: checkmk.com
Status: Confirmed

CVE: CVE-2025-64999 (🔒)
GCVE (CVE): GCVE-0-2025-64999
GCVE (VulDB): GCVE-100-347977
CERT Bund: WID-SEC-2026-0543 - Checkmk: Schwachstelle ermöglicht Cross-Site Scripting

Entryinfo

Created: 02/26/2026 15:17
Updated: 03/06/2026 00:22
Changes: 02/26/2026 15:17 (66), 02/27/2026 19:01 (7), 03/02/2026 15:33 (12), 03/06/2026 00:22 (2)
Complete: 🔍
Cache ID: 216::103

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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