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.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
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
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.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-81909 being exploited?
There is no known exploitation of CVE-2026-81909 in the wild and no public exploit code.
Sources
Also known as GHSA-9xmc-5q7j-x4fm.