CVE-2026-18421: 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

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

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.

Description from the National Vulnerability Database, published by ff5b8ace-8b95-4078-9743-eac1ca5451de

What it means for a small business

If your business uses Concrete CMS, install the vendor's update. If you're not sure whether you use it, ask whoever manages your computers.

How likely is an attack? The Exploit Prediction Scoring System, run by FIRST (the global association of security response teams), puts the odds of this one being exploited in the next 30 days at 0.44%, higher than 38% of CVEs. That’s low, but low isn’t zero, and the odds jump the day someone publishes an exploit. Scored October 28, 2026, updated daily.

Check your own setup

Website check: reads what your site runs from the outside (WordPress version, plugins it can see, old server software) and matches it against this database.
Server check: what your web server says about itself, and whether that version has known flaws.

Sources

Part of the Huttenlocher Technologies vulnerability database, refreshed twice a day from CISA and the NVD. The title, category and plain-language guidance are ours; check the linked record before acting on a detail. This is general guidance, not a review of your systems.

Weekly security brief

The flaws that hit local websites, every Friday.

One short email: what got exploited this week, which WordPress plugins broke, and what to check. Unsubscribe in one click.