CVE-2021-40108 in Concrete
Summary
by MITRE • 09/27/2021
An issue was discovered in Concrete CMS through 8.5.5. The Calendar is vulnerable to CSRF. ccm_token is not verified on the ccm/calendar/dialogs/event/add/save endpoint.
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Analysis
by VulDB Data Team • 10/02/2021
The vulnerability identified as CVE-2021-40108 affects Concrete CMS versions through 8.5.5 and represents a critical cross-site request forgery flaw within the calendar module. This weakness resides in the ccm/calendar/dialogs/event/add/save endpoint where the system fails to properly validate the ccm_token parameter that should serve as a protective mechanism against unauthorized requests. The absence of token verification creates a significant security gap that allows attackers to execute malicious actions on behalf of authenticated users without their knowledge or consent.
This vulnerability operates under the broader category of CWE-352 - Cross-Site Request Forgery, which is classified as a critical weakness in web applications where the system fails to validate that requests originate from legitimate sources. The specific implementation flaw in Concrete CMS demonstrates a failure in the application's anti-CSRF protection mechanisms, where the expected security token validation is bypassed entirely. The calendar event addition functionality becomes a vector for exploitation, allowing malicious actors to manipulate calendar entries through crafted requests that appear to come from legitimate users within the system.
The operational impact of this vulnerability extends beyond simple data manipulation as it enables attackers to perform unauthorized calendar event creation, modification, or deletion operations. An attacker could potentially schedule malicious events, disrupt calendar functionality, or use the calendar module as a stepping stone for further exploitation within the CMS environment. The vulnerability particularly affects authenticated users since the attack requires valid session credentials to be effective, though the lack of token verification means that even a single compromised session could be exploited. This weakness also aligns with ATT&CK technique T1566.002 - Phishing via Service, where attackers might leverage calendar functionality as part of broader social engineering campaigns.
Mitigation strategies for this vulnerability should focus on implementing proper token validation at the affected endpoint, ensuring that all requests to the calendar event management functionality require valid ccm_token verification before processing. Organizations should immediately upgrade to Concrete CMS version 8.5.6 or later where this issue has been addressed through proper token validation implementation. Additional defensive measures include implementing Content Security Policy headers, enabling additional authentication layers for administrative functions, and monitoring for unusual calendar activity patterns that might indicate exploitation attempts. The fix should also include comprehensive input validation and proper session management to ensure that all administrative endpoints require proper authorization tokens before executing any destructive operations.