CVE-2026-2994: Concrete CMS CSRF Vulnerability

CVE-2026-2994 Overview

A Cross-Site Request Forgery (CSRF) vulnerability exists in Concrete CMS versions below 9.4.8 that allows a rogue administrator to exploit the Anti-Spam Allowlist Group Configuration via the group_id parameter. This vulnerability enables a security bypass because configuration changes are saved prior to validating the CSRF token, allowing unauthorized modifications to the anti-spam allowlist settings.

Critical Impact

A malicious actor with administrative access can leverage this CSRF flaw to bypass security controls and modify anti-spam allowlist configurations without proper CSRF token validation, potentially allowing spam or malicious content to bypass filtering mechanisms.

Affected Products

• Concrete CMS versions below 9.4.8
• concretecms concrete_cms (all versions prior to patched release)

Discovery Timeline

• 2026-03-04 - CVE-2026-2994 published to NVD
• 2026-03-04 - Last updated in NVD database

Technical Details for CVE-2026-2994

Vulnerability Analysis

This CSRF vulnerability (CWE-352) exists in Concrete CMS's Anti-Spam Allowlist Group Configuration functionality. The core issue stems from the application's improper handling of state-changing operations, where modifications to group configurations are persisted to the database before the CSRF token validation occurs. This order-of-operations flaw means that even if the CSRF check ultimately fails, the malicious changes have already been saved.

The vulnerability requires an attacker to craft a malicious request that targets the group configuration endpoint, specifically manipulating the group_id parameter. When an authenticated administrator is tricked into executing this request (via a malicious link or embedded content), the configuration changes take effect before any security validation can prevent them.

Root Cause

The root cause lies in the improper sequencing of security checks within the Anti-Spam Allowlist Group Configuration handler. The application processes and commits data modifications before validating the CSRF token, violating secure coding practices that mandate authentication and authorization checks should occur before any state-changing operations. This classic TOCTOU (time-of-check-time-of-use) pattern creates a window where unauthorized changes can be persisted regardless of subsequent security validation outcomes.

Attack Vector

The attack requires network access and involves social engineering an authenticated administrator into clicking a crafted link or visiting a page containing a malicious form. The attacker constructs a request targeting the vulnerable endpoint with a manipulated group_id parameter. When the victim's browser submits this request with their valid session credentials, the server processes the modification before checking CSRF protections.

The vulnerability's network-based attack vector combined with the requirement for user interaction (the administrator must be tricked into triggering the request) and the need for the attacker to have some level of privileges limits the overall impact. However, successful exploitation can lead to integrity violations in the anti-spam configuration.

Detection Methods for CVE-2026-2994

Indicators of Compromise

• Unexpected modifications to Anti-Spam Allowlist Group configurations without corresponding administrative actions
• Audit log entries showing group configuration changes with unusual referrer headers or request patterns
• Changes to group_id settings that administrators did not authorize

Detection Strategies

• Monitor HTTP POST requests to Anti-Spam Allowlist configuration endpoints for suspicious referrer headers indicating cross-origin submissions
• Implement web application firewall (WAF) rules to detect CSRF attack patterns targeting Concrete CMS administrative functions
• Review application logs for configuration changes that lack corresponding valid CSRF tokens

Monitoring Recommendations

• Enable comprehensive audit logging for all administrative configuration changes in Concrete CMS
• Configure alerting for any Anti-Spam Allowlist modifications outside of expected maintenance windows
• Implement SentinelOne Singularity XDR to detect anomalous web application behavior and potential CSRF exploitation attempts

How to Mitigate CVE-2026-2994

Immediate Actions Required

• Upgrade Concrete CMS to version 9.4.8 or later immediately
• Review Anti-Spam Allowlist Group configurations for any unauthorized modifications
• Audit administrative user sessions and force re-authentication if CSRF exploitation is suspected
• Implement additional CSRF protections at the WAF level as a defense-in-depth measure

Patch Information

The Concrete CMS development team has addressed this vulnerability in version 9.4.8. The fix ensures that CSRF token validation occurs before any configuration changes are persisted to the database. Administrators should review the Concrete CMS 9.4.8 Release Notes for complete details. The specific code changes can be reviewed in GitHub Pull Request #12826.

Workarounds

• Limit administrative access to trusted networks only until the patch can be applied
• Implement strict Content Security Policy (CSP) headers to reduce cross-origin attack surface
• Train administrators to be cautious of clicking links while logged into Concrete CMS administrative sessions
• Consider deploying a reverse proxy with CSRF protection capabilities as an additional layer of defense