CVE-2026-90990: CWE-93: Improper Neutralization of CRLF Sequences ('CRLF Injection') in Checkmk GmbH Checkmk
Improper neutralization of newlines in filter values in the monitoring host and service list APIs in Checkmk <2.5.0p14 allows an authenticated user to inject additional Livestatus query headers, bypassing object visibility restrictions in count queries to infer information about hosts and services outside their contact groups and occupying web server and Livestatus workers for an attacker-controlled duration.
AI Analysis
Technical Summary
This vulnerability (CVE-2026-90990) affects Checkmk versions >=2.5.0 and <2.5.0p14. It is caused by improper neutralization of newline characters (CRLF injection) in filter values used by the monitoring host and service list APIs. Exploitation allows an authenticated user to inject additional Livestatus query headers, which bypasses object visibility restrictions in count queries. This enables the attacker to infer information about hosts and services outside their assigned contact groups and to occupy web server and Livestatus worker resources for a duration controlled by the attacker. The CVSS 4.0 base score is 5.3, indicating medium severity.
Potential Impact
An authenticated user can bypass object visibility restrictions to gain information about hosts and services outside their contact groups. Additionally, the vulnerability can be used to occupy web server and Livestatus worker resources, potentially impacting service availability or performance.
Mitigation Recommendations
A fix is available in Checkmk version 2.5.0p14. Users should upgrade to this version or later to remediate the vulnerability. No additional mitigation steps are indicated.
CVE-2026-90990: CWE-93: Improper Neutralization of CRLF Sequences ('CRLF Injection') in Checkmk GmbH Checkmk
Description
Improper neutralization of newlines in filter values in the monitoring host and service list APIs in Checkmk <2.5.0p14 allows an authenticated user to inject additional Livestatus query headers, bypassing object visibility restrictions in count queries to infer information about hosts and services outside their contact groups and occupying web server and Livestatus workers for an attacker-controlled duration.
CVSS v4.0
Score 5.3medium
Affected software
Checkmk GmbH
Checkmk
pkg:github/checkmk/checkmkRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
This vulnerability (CVE-2026-90990) affects Checkmk versions >=2.5.0 and <2.5.0p14. It is caused by improper neutralization of newline characters (CRLF injection) in filter values used by the monitoring host and service list APIs. Exploitation allows an authenticated user to inject additional Livestatus query headers, which bypasses object visibility restrictions in count queries. This enables the attacker to infer information about hosts and services outside their assigned contact groups and to occupy web server and Livestatus worker resources for a duration controlled by the attacker. The CVSS 4.0 base score is 5.3, indicating medium severity.
Potential Impact
An authenticated user can bypass object visibility restrictions to gain information about hosts and services outside their contact groups. Additionally, the vulnerability can be used to occupy web server and Livestatus worker resources, potentially impacting service availability or performance.
Mitigation Recommendations
A fix is available in Checkmk version 2.5.0p14. Users should upgrade to this version or later to remediate the vulnerability. No additional mitigation steps are indicated.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- Checkmk
- Date Reserved
- 2026-09-14T14:17:32.990Z
- Cvss Version
- 4.0
- State
- PUBLISHED
Threat ID: 6ab25cf3f7a7c541060f745a
Added to database: 09/22/2026, 10:48:19 UTC
Last enriched: 09/22/2026, 11:02:45 UTC
Last updated: 09/23/2026, 01:58:07 UTC
Views: 16
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