VDB-369187 · CVE-2026-8833 · EUVD-2026-35053

Checkmk up to 2.2.0/2.3.0p47/2.4.0p30/2.5.0p4 URL Validation cross site scripting

CVSS Meta Temp Score CVSS is a standardized scoring system to determine possibilities of attacks. The Temp Score considers temporal factors like disclosure, exploit and countermeasures. The unique Meta Score calculates the average score of different sources to provide a normalized scoring system.	Current Exploit Price (≈) Our analysts are monitoring exploit markets and are in contact with vulnerability brokers. The range indicates the observed or calculated exploit price to be seen on exploit markets. A good indicator to understand the monetary effort required for and the popularity of an attack.	CTI Interest Score Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
3.4	$0-$5k	0.00

Summaryinfo

A vulnerability was found in Checkmk up to 2.2.0/2.3.0p47/2.4.0p30/2.5.0p4. It has been rated as problematic. Impacted is an unknown function of the component URL Validation Handler. This manipulation causes cross site scripting. This vulnerability is tracked as CVE-2026-8833. The attack is possible to be carried out remotely. No exploit exists. Upgrading the affected component is advised.

Detailsinfo

A vulnerability was found in Checkmk up to 2.2.0/2.3.0p47/2.4.0p30/2.5.0p4. It has been declared as problematic. Affected by this vulnerability is an unknown function of the component URL Validation Handler. The manipulation with an unknown input leads to a cross site scripting 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 HTML-encoded characters in the URL validation function in Checkmk <2.5.0p5, <2.4.0p31, <2.3.0p48, and all 2.2.0 versions allows an authenticated user to bypass URL validation and inject malicious URLs such as javascript: URIs, resulting in cross-site scripting when another user interacts with the crafted link.

It is possible to read the advisory at checkmk.com. This vulnerability is known as CVE-2026-8833 since 05/18/2026. The exploitation appears to be easy. The attack can be launched remotely. It demands that the victim is doing some kind of user interaction. The technical details are unknown and an exploit is not publicly available. The attack technique deployed by this issue is T1059.007 according to MITRE ATT&CK.

Upgrading to version 2.3.0p48, 2.4.0p31 or 2.5.0p5 eliminates this vulnerability.

The vulnerability is also documented in the databases at EUVD (EUVD-2026-35053) and CERT Bund (WID-SEC-2026-1817). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Affected

Checkmk Checkmk

Productinfo

Name

Checkmk

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: 3.5
VulDB Meta Temp Score: 3.4

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

CVSSv2info

AV	AC	Au	C	I	A
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Vector	Complexity	Authentication	Confidentiality	Integrity	Availability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Cross site scripting
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: 🔒

0-Day	Unlock	Unlock	Unlock	Unlock
Today	Unlock	Unlock	Unlock	Unlock

Threat Intelligenceinfo

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

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Checkmk 2.3.0p48/2.4.0p31/2.5.0p5

Timelineinfo

05/18/2026 CVE reserved
06/08/2026 +21 days Advisory disclosed
06/08/2026 +0 days VulDB entry created
06/09/2026 +1 days VulDB entry last update

Sourcesinfo

Advisory: checkmk.com
Status: Confirmed

CVE: CVE-2026-8833 (🔒)
GCVE (CVE): GCVE-0-2026-8833
GCVE (VulDB): GCVE-100-369187
EUVD: 🔒
CERT Bund: WID-SEC-2026-1817 - Checkmk: Mehrere Schwachstellen ermöglichen Cross-Site Scripting

Entryinfo

Created: 06/08/2026 15:17
Updated: 06/09/2026 11:55
Changes: 06/08/2026 15:17 (66), 06/08/2026 17:31 (1), 06/09/2026 11:55 (7)
Complete: 🔍
Cache ID: 216::103

Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.