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.
- 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-2026-18421?
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
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.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-18421 being exploited?
There is no known exploitation of CVE-2026-18421 in the wild and no public exploit code.
Sources
Also known as GHSA-266p-gm36-gqvf.