CVE-2026-121374: Checkmk file write and code execution

Q: 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.

Q: 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.

Q: 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.

Q: 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.

Q: 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.

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.

Read the original 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.

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

Read the source excerpt

“All sites are affected.”

checkmk.com

cve.now Index

17Pcve.now Index 17 of 100 · methodology v3 · provisional

Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
Exposure8/25Specific setups only, reachable over the network
Reach?/20Unknown. No tracked technology or package matched
Severity9.4/10CVSS 9.4
No patch0/5No signal

What would change the score

Would score about 67 if added to CISA KEV
Would score about 62 if CISA's SSVC rates exploitation active
Would score about 24 if CISA's SSVC rates it automatable

How the score works · Rankings

What to do

Check whether your setup matches what the bug needs.
Kubernetes special agent using the 'Exclude nodes based on their role' rule option with crafted node roles
Upgrade to a fixed version: 2.5.0p19, 2.4.0p40.

Check your systems with an agent

Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.

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.

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.

Timeline

Nov 11, 2026, 10:45 AM UTCCVE published
Nov 11, 2026, 10:51 AM UTCRecord last updated
Nov 11, 2026, 10:54 AM UTCFirst seen by cve.now
Nov 11, 2026, 11:07 AM UTCPosted on X by cve.now

Affected versions

Checkmk GmbH Checkmk
From 2.5.0 · fixed in 2.5.0p19; From 2.4.0 · fixed in 2.4.0p40

Evidence 4

Vendor advisory · 2

Establishes: Affected and fixed versions.

Advisory
checkmk.com · werk/17994
Advisory
checkmk.com · werk/22120

CVE record · 2

Establishes: The identifier and description.

Record
CVE List · CVE-2026-121374
Record
NVD · CVE-2026-121374

Corrections

None so far.

Something wrong on this page? Report an error. Every fix is listed here.

Questions about CVE-2026-121374

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: cve.now feed data

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: checkmk.com

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: cve.now feed data

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: checkmk.com

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: checkmk.com

Arbitrary file write and code execution via excluded node roles in Kubernetes special agent