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

> Unauthenticated attackers can enumerate existing hosts by observing response discrepancies in the deploy agent endpoint, leading to information disclosure.

- **Severity:** Medium 6.3 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 13 Mar 2026
- **Updated:** 13 Mar 2026
- **Also known as:** GHSA-xxw2-9c45-r2hr, UBUNTU-CVE-2026-2859

## What is CVE-2026-2859?

CVE-2026-2859 is a medium-severity vulnerability in Checkmk Checkmk, published on 13 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-204 (Observable Response Discrepancy)

## Which versions are affected by CVE-2026-2859?

It affects 1 product.


Products: Checkmk Checkmk.

## How do I fix CVE-2026-2859?

No fix has been published for CVE-2026-2859 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-2859 being exploited?

There is no known exploitation of CVE-2026-2859 in the wild and no public exploit code.

## Other vulnerabilities in Checkmk Checkmk

- [CVE-2025-39666](https://insights.sbomify.com/CVE-2025-39666/): omd: Local privilege escalation when executing omd commands as root (critical 9.3)
- [CVE-2024-8606](https://insights.sbomify.com/CVE-2024-8606/): Fix 2FA bypass via RestAPI (critical 9.2)
- [CVE-2022-46836](https://insights.sbomify.com/CVE-2022-46836/): PHP code injection in watolib (critical 9.1)
- [CVE-2025-32919](https://insights.sbomify.com/CVE-2025-32919/): Privilege Escalation in Windows License plugin for Checkmk Windows Agent (high 8.8)
- [CVE-2024-28827](https://insights.sbomify.com/CVE-2024-28827/): Privilege escalation in Windows agent (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-2859 and fix it if it is affected.

What it is: CVE-2026-2859 is a medium-severity vulnerability in Checkmk Checkmk, published on 13 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-2859 in the wild and no public exploit code.

Affected product: Checkmk Checkmk. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-2859/ (Markdown: https://insights.sbomify.com/CVE-2026-2859/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-2859
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-2859
- OSV: https://osv.dev/vulnerability/CVE-2026-2859

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-2859/
Summaries are generated and may contain mistakes; the official description above is the record.