Checkmk: Argument injection in Kubernetes special agent
Summary
Checkmk versions 2.5.0 before 2.5.0p19, 2.4.0 before 2.4.0p40 and 2.3.0 (EOL) contain an argument injection flaw in the Kubernetes special agent. A user who may edit rules in at least one folder can enter crafted node roles in the rule option Exclude nodes based on their role, and the agent reads them as its own command line options, including the debugging option --profile. This allows the user to write files to any location writable by the site user, which leads to code execution as the site user. The attacker does not need Kubernetes monitoring in use, because the rule can be created without it.
Affected
- Checkmk 2.5.0 before 2.5.0p19
- Checkmk 2.4.0 before 2.4.0p40
- Checkmk 2.3.0 (EOL): listed as affected in the CVE record, no fixed release; the record also notes 2.3.0 as unaffected by default
- Precondition: a user with permission to edit rules in at least one folder; by default this includes users with the role Normal monitoring user who have folder permissions
Fixed in
- Checkmk 2.5.0p19
- Checkmk 2.4.0p40
- Checkmk 2.3.0: no fixed release; the branch is end of life and should be migrated to a supported, patched version
Workaround
- Unknown. The vendor data indicates no other mitigation; applying the official patches fully addresses the issue.
- Own suggestion, not from the vendor: until patching is complete, review and reduce who holds rule-edit rights in Checkmk folders.
Exploitation
- No evidence of exploitation in the wild in the sources reviewed.
- No public proof-of-concept or exploit code found in the sources reviewed at the time of research. The CVE is very recent, so this may change.
Our recommendation
- Identify all Checkmk instances and their versions, including any 2.3.0 installations.
- Upgrade to 2.5.0p19 or 2.4.0p40; plan migration away from 2.3.0.
- Review and reduce rule-edit permissions in Checkmk folders.
- Confirm the Checkmk web interface is not internet-exposed, or is only reachable via VPN or MFA, and that no default or weak credentials are in use.
- The same versions also fix CVE-2026-120495; one upgrade covers both.
- Re-check the Werk and NVD for updates.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Checkmk Werk #17994 (vendor advisory) checkmk.com
- OffSeq: CVE-2026-121374 details radar.offseq.com
- OffSeq: CVE-2026-120495 (same fixed versions) radar.offseq.com
- Checkmk download page checkmk.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 11 Nov 2026, 12:21.
Original description (NVD)
Argument injection in the Kubernetes special agent in Checkmk <2.5.0p19, <2.4.0p40, and 2.3.0 (EOL) allows a user with permission to edit rules in at least one folder to write files to arbitrary locations writable by the site user via crafted node roles in the "Exclude nodes based on their role" rule option, leading to code execution as the site user.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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