# CVE-2026-81909

## Summary

- **CVE ID:** CVE-2026-81909
- **Severity:** MEDIUM
- **CVSS Score:** 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)
- **CWE:** CWE-862
- **Published:** Sep 11, 2026
- **Last Modified:** Sep 11, 2026

## 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.

## Affected Products

- Concrete CMS — Concrete CMS (9.0.0)

## References

- [CNA](https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes)

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._