CVE-2025-62400 is a vulnerability identified in multiple recent versions of Moodle, a widely used open-source learning management system. The flaw arises because Moodle exposes the names of hidden groups to users who have the permission to create calendar events, even if those users do not have permission to view hidden groups. This results in an unauthorized disclosure of sensitive information about group membership or existence, which could be leveraged for social engineering or to infer organizational structures. The vulnerability has a CVSS v3.1 base score of 4.3, categorized as medium severity, reflecting its limited impact on confidentiality and no impact on integrity or availability. Exploitation requires the user to have calendar event creation privileges, which is a low-level privilege in many Moodle deployments, and does not require user interaction beyond normal use. The vulnerability is network exploitable and does not require elevated privileges beyond the calendar event creation permission. No known exploits have been reported in the wild, and no official patches have been linked at the time of publication. The issue highlights the importance of strict access control and information disclosure policies within Moodle's permission model, especially concerning hidden groups and calendar functionalities.

For European organizations, especially educational institutions and public sector entities that heavily rely on Moodle for course management and collaboration, this vulnerability could lead to unintended exposure of private group information. Such exposure may violate privacy regulations like GDPR if personal or sensitive data about group membership is revealed. It could also undermine trust in the platform and expose organizational structures or confidential project groups to unauthorized users. While the impact does not extend to data modification or service disruption, the confidentiality breach could facilitate targeted phishing or social engineering attacks. Organizations with large user bases and complex group hierarchies are at greater risk. The medium severity rating indicates that while the risk is not critical, it should be addressed promptly to maintain compliance and security posture.

To mitigate this vulnerability, European organizations should immediately review and restrict permissions related to calendar event creation, limiting this capability to trusted users only. Administrators should audit group visibility settings to ensure hidden groups are properly configured and inaccessible to unauthorized users. Monitoring user activity logs for unusual access patterns to calendar features can help detect potential exploitation attempts. Until official patches are released, consider implementing custom access control rules or plugins to enforce stricter separation between calendar event creation permissions and group visibility. Additionally, organizations should stay informed about Moodle security advisories and apply updates promptly once patches addressing CVE-2025-62400 become available. User training on the risks of information disclosure and phishing can also reduce the impact of any leaked group information.