CVE-2026-81924 Overview
CVE-2026-81924 is a Cross-Site Request Forgery (CSRF) vulnerability [CWE-352] in Concrete CMS versions before 9.5.3. The flaw resides in the Dashboard theme Inspect controller's activate_files() action. This action creates PageTemplate records from attacker-supplied pageTemplates[] values without validating an anti-CSRF token. A remote attacker can host a page that auto-submits a forged POST request. When a signed-in administrator visits the attacker-controlled page, the request executes under the administrator's session and creates theme page-template records, modifying site configuration without consent.
Critical Impact
An attacker can trick an authenticated administrator into unknowingly creating theme page-template records, altering site configuration without approval.
Affected Products
- Concrete CMS versions prior to 9.5.3
- Dashboard theme Inspect controller (activate_files() action)
- Sites where administrators are authenticated during browsing sessions
Discovery Timeline
- Vulnerability reported by Andrew Gonzalez
- 2026-09-15 - CVE-2026-81924 published to NVD
- 2026-09-16 - Last updated in NVD database
Technical Details for CVE-2026-81924
Vulnerability Analysis
The vulnerability exists in the Dashboard theme Inspect controller within Concrete CMS. The activate_files() action accepts an array of values via the pageTemplates[] parameter and uses them to create PageTemplate records. The controller processes these state-changing POST requests without verifying the presence or validity of an anti-CSRF token.
Because the endpoint requires an authenticated administrator session, exploitation relies on session-riding. An attacker crafts a malicious HTML page containing a form or script that automatically submits a forged POST request to the vulnerable endpoint. When a signed-in administrator loads the attacker-controlled page in the same browser, the browser attaches the administrator's session cookies. The server processes the request as if the administrator initiated it, creating theme page-template records and modifying site configuration silently.
The scope of impact is limited to low-integrity configuration changes. Confidentiality and availability are not directly affected. However, unauthorized configuration changes can serve as a foothold for follow-on attacks against the CMS.
Root Cause
The root cause is missing anti-CSRF token validation on a state-changing controller action. The activate_files() action in the Dashboard theme Inspect controller trusts the origin of the request based solely on session cookies. It does not verify a per-request or per-session token bound to the administrator's browser context.
Attack Vector
Exploitation requires an authenticated administrator to visit an attacker-controlled page while their Concrete CMS session is active. The attacker hosts a page that auto-submits a forged POST request containing crafted pageTemplates[] values to the vulnerable endpoint. High privileges are required on the victim side, and no direct user interaction with the payload is needed beyond visiting the malicious page.
No verified public exploit code is available. Refer to the Concrete CMS 9.5.3 Release Notes for vendor-provided technical detail.
Detection Methods for CVE-2026-81924
Indicators of Compromise
- Unexpected creation of PageTemplate records in the Concrete CMS database that do not correspond to legitimate administrator activity.
- POST requests to the Dashboard theme Inspect controller's activate_files() endpoint with a Referer header pointing to an external or unfamiliar domain.
- Configuration changes to theme page-templates occurring outside normal change-management windows.
Detection Strategies
- Enable web server access logging and review POST requests to Dashboard theme controller endpoints for anomalous Referer or Origin headers.
- Correlate administrator session activity with theme configuration changes to identify requests initiated from third-party domains.
- Alert on repeated POST submissions to activate_files() from browsers with cross-origin referers.
Monitoring Recommendations
- Monitor Concrete CMS audit logs for creation of new PageTemplate records and attribute each change to a specific administrator session.
- Track HTTP request patterns to /dashboard/ administrative endpoints and flag requests lacking a same-origin Referer.
- Establish a baseline for theme-configuration change frequency and alert on deviations.
How to Mitigate CVE-2026-81924
Immediate Actions Required
- Upgrade Concrete CMS to version 9.5.3 or later, which introduces CSRF token validation on the affected controller action.
- Audit existing PageTemplate records and revert any unauthorized entries created before the patch was applied.
- Instruct administrators to log out of the CMS Dashboard when not actively performing administrative tasks.
Patch Information
Concrete CMS addressed CVE-2026-81924 in version 9.5.3. The fix adds anti-CSRF token validation to the Dashboard theme Inspect controller's activate_files() action. Refer to the Concrete CMS 9.5.3 Release Notes for the complete list of security fixes included in the release.
Workarounds
- Restrict access to the Dashboard by IP allow-listing at the web server or reverse proxy layer until the patch is applied.
- Require administrators to use a dedicated browser or browser profile for CMS administration to isolate session cookies from general browsing.
- Enforce SameSite=Strict on administrator session cookies to reduce the risk of cross-site request forgery against authenticated sessions.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.