CVE-2025-39663

Cross Site Scripting through compromised remote site

8.5 High

Cross-Site Scripting (XSS) vulnerability in Checkmk's distributed monitoring allows a compromised remote site to inject malicious HTML code into service outputs in the central site. Affecting Checkmk before 2.4.0p14, 2.3.0p39, 2.2.0 and 2.1.0 (eol).

Attack profile

How easy it is to exploit

Attack vector: Network
Complexity: Low
Privileges needed: High
User interaction: Passive

What an attacker can affect

Confidentiality: High
Integrity: High
Availability: High

Exploit likelihood

0.60%Up 0.6 points since Oct 30, 2025

What each source reports

CVE List Score used 8.5

Cross Site Scripting through compromised remote site

Record: CVE-2025-39663
CVSS 4.0: 8.5 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
Weakness: CWE-80
Updated: 2026-11-02

EUVDEUVD-2025-36997 8.5

Record: EUVD-2025-36997
CVSS 4.0: 8.5 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
Updated: 2026-11-02

GitHub AdvisoriesGHSA-m8fq-fxf8-wxx3 8.5

Cross-Site Scripting (XSS) vulnerability in Checkmk's distributed monitoring allows a compromised...

Record: GHSA-m8fq-fxf8-wxx3
CVSS 4.0: 8.5 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS 3.1: 8.4 HighCVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:H/I:H/A:H
Weakness: CWE-79, CWE-80
Updated: 2026-11-02

NVD 8.5

Record: CVE-2025-39663
CVSS 4.0: 8.5 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS 3.1: 8.4 HighCVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:H/I:H/A:H
Weakness: CWE-80, CWE-79
Updated: 2026-11-02

OSV 8.5

Cross Site Scripting through compromised remote site

Record: CVE-2025-39663
CVSS 4.0: 8.5 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
Weakness: CWE-80
Updated: 2026-11-02

OSVUBUNTU-CVE-2025-39663 8.5

Record: UBUNTU-CVE-2025-39663
CVSS 4.0: 8.5 HighCVSS: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 3.1: 8.4 HighCVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:H/I:H/A:H
Updated: 2026-11-02

Affected products

Affected packages

Affected packages
Package	Affected	Fixed
`check-mk` Ubuntu:Pro:16.04:LTS	All versions, plus listed versions 1.2.6p5-11.2.6p12-11.2.6p12-1ubuntu0.16.04.11.2.6p12-1ubuntu0.16.04.1+esm1	None known
`check-mk` Ubuntu:18.04:LTS	All versions, plus listed versions 1.2.8p16-1ubuntu0.11.2.8p16-1ubuntu0.2	None known

History

History
Recorded	Changed	Sources
Nov 2, 2026	first indexed	CVE List, EUVD, GitHub Advisories, NVD, OSV

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

In short

CVE-2025-39663 is a high vulnerability (CVSS 8.5) in Checkmk, published October 30, 2025. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.60%, the 49th percentile. No source names a fixed version.