Executive brief
Concrete CMS, a popular web content management system, is vulnerable to an issue where an attacker can trick an administrator into performing a core system update. By convincing a logged-in administrator to visit a malicious website, the attacker can trigger a background request that forces the CMS to update to a specific version. This could lead to unauthorized system changes or service disruption if the administrator has the necessary permissions and update files are present on the server.
Technical details
A Cross-Site Request Forgery (CSRF) vulnerability exists in Concrete CMS versions 9.5.0 and below. While the 'local_available_update.php' view generates a CSRF token, the 'do_update()' method in the 'Update' controller fails to validate this token. An attacker can exploit this by crafting a malicious web page that sends a cross-site POST request to the dashboard update endpoint. If a victim with 'canUpgrade()' permissions is authenticated and a valid update version exists in the 'DIR_CORE_UPDATES' directory, the attacker can force the CMS to update to a version string of their choosing. This issue is resolved in version 9.5.1.
Affected products
- Concrete CMS Concrete CMS <= 9.5.0
Timeline
- 2026-05-21: disclosed
- 2026-05-21: advisory
- 2026-06-24: patched: Advisory updated with patch details for version 9.5.1