# CVE-2026-81909: Missing authorization in Concrete CMS

> An authenticated editor can disclose and delete arbitrary blocks due to missing authorization checks in the block alias route.

- **Severity:** Medium 5.9 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:N/VI:H/VA:H/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:** 11 Sep 2026
- **Updated:** 11 Sep 2026
- **Also known as:** GHSA-9xmc-5q7j-x4fm

## What is CVE-2026-81909?

CVE-2026-81909 is a medium-severity missing authorization vulnerability in Concrete CMS, published on 11 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 is vulnerable to Missing Authorization in the block alias route (Process::alias() in concrete/controllers/backend/block/process.php).It does not verify that the referenced block is genuinely orphaned on the target page, nor that the caller holds any permission over the source block. A user granted only an area-scoped add_block_to_area delegation on their own page can therefore pass any block ID on the site: the source block's content is duplicated into an area the rogue editor controls, disclosing that content, and the original block is then force-deleted in the same request, destroying arbitrary site content. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 5.9 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N. Thanks Yonatan Drori from Tenzai for reporting.

Weakness: CWE-862 (Missing Authorization)

## Which versions are affected by CVE-2026-81909?


## How do I fix CVE-2026-81909?

No fix has been published for CVE-2026-81909 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-81909 being exploited?

There is no known exploitation of CVE-2026-81909 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-81909 and fix it if it is affected.

What it is: CVE-2026-81909 is a medium-severity missing authorization vulnerability in Concrete CMS, published on 11 Sep 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-81909 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-2026-81909/ (Markdown: https://insights.sbomify.com/CVE-2026-81909/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-81909
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-81909
- OSV: https://osv.dev/vulnerability/CVE-2026-81909

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-81909/
Summaries are generated and may contain mistakes; the official description above is the record.