# CVE-2026-18421: Missing authorization in Concrete CMS

> Low-privileged board editors can modify or delete data sources on boards they do not control due to missing authorization checks in Concrete CMS.

- **Severity:** Low 2.1 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 15 Sep 2026
- **Updated:** 15 Sep 2026
- **Also known as:** GHSA-266p-gm36-gqvf

## What is CVE-2026-18421?

CVE-2026-18421 is a low-severity missing authorization vulnerability in Concrete CMS, published on 15 Sep 2026. An attacker needs administrator access to exploit it, with no action from the victim.

### Official description

Concrete CMS 9 through 9.5.2 does not perform an authorization check in three actions of the Boards data source dashboard controller (update, update_data_source, and delete_data_source), which resolve a ConfiguredDataSource directly from an attacker-supplied identifier without confirming the requester's edit permission on the owning board. A user granted edit_board_settings on a single board was therefore able to modify or permanently delete the configured data sources of any other board on the site, halting the affected board's content feed and resetting its custom weighting. The CSRF token that guards these actions was validated but bound to the action name rather than to the target object, so a token legitimately obtained for one board could be replayed against another board's ConfiguredDataSource identifier and did not constrain access. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 2.1 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N. Thanks Winston Crooker for reporting.

Weakness: CWE-862 (Missing Authorization)

## Which versions are affected by CVE-2026-18421?


## How do I fix CVE-2026-18421?

No fix has been published for CVE-2026-18421 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-18421 being exploited?

There is no known exploitation of CVE-2026-18421 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-18421 and fix it if it is affected.

What it is: CVE-2026-18421 is a low-severity missing authorization vulnerability in Concrete CMS, published on 15 Sep 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-18421 in the wild and no public exploit code.

Affected product: Concrete CMS. 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-2026-18421/ (Markdown: https://insights.sbomify.com/CVE-2026-18421/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-18421
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-18421
- OSV: https://osv.dev/vulnerability/CVE-2026-18421

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-18421/
Summaries are generated and may contain mistakes; the official description above is the record.