CVE-2016-2156 in Moodle
Summary
by MITRE
calendar/externallib.php in Moodle through 2.6.11, 2.7.x before 2.7.13, 2.8.x before 2.8.11, 2.9.x before 2.9.5, and 3.0.x before 3.0.3 provides calendar-event data without considering whether an activity is hidden, which allows remote authenticated users to obtain sensitive information via a web-service request.
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Analysis
by VulDB Data Team • 08/21/2022
The vulnerability identified as CVE-2016-2156 affects Moodle learning management systems across multiple versions including 2.6.11 and earlier, 2.7.x versions before 2.7.13, 2.8.x versions before 2.8.11, 2.9.x versions before 2.9.5, and 3.0.x versions before 3.0.3. This issue resides in the calendar/externallib.php file which handles calendar event data through web service requests. The flaw represents a critical information disclosure vulnerability that undermines the system's access control mechanisms and data protection protocols.
The technical implementation flaw occurs when Moodle processes calendar-event data through its external web service interface without properly validating whether individual activities are marked as hidden or restricted. This oversight creates a scenario where authenticated users can exploit the calendar web service to retrieve calendar-event information that should remain inaccessible due to hidden status flags. The vulnerability specifically targets the external library component that manages calendar data exposure, bypassing the normal access control checks that would typically prevent unauthorized viewing of hidden activities.
Operationally, this vulnerability allows remote authenticated attackers to gain unauthorized access to sensitive calendar information that should be restricted to specific users or roles. Attackers can leverage this flaw to discover hidden course activities, assignments, or events that are not intended for general viewing. The impact extends beyond simple information disclosure as it can reveal organizational structures, course schedules, and activity timelines that may contain confidential educational or administrative data. This type of vulnerability directly violates the principle of least privilege and can enable further attacks by providing attackers with intelligence about system components and user access patterns.
The vulnerability maps to CWE-200 (Information Exposure) and aligns with ATT&CK technique T1213 (Data from Information Repositories) in its exploitation methodology. Organizations using affected Moodle versions face significant risks including potential exposure of student schedules, assignment deadlines, and course structures that could be used for social engineering or targeted attacks. The attack surface is particularly concerning as it requires only authenticated access, meaning that any user with valid credentials can potentially exploit this vulnerability to gather sensitive information about hidden course elements.
Mitigation strategies should focus on immediate patch application to the affected Moodle versions, ensuring all systems are updated to the latest stable releases that contain the necessary security fixes. Administrators should also implement additional monitoring of calendar web service usage and consider implementing more granular access controls for calendar data. The vulnerability demonstrates the importance of proper input validation and access control implementation in web service interfaces, particularly when dealing with user-specific data that may have varying visibility settings. Security teams should conduct thorough audits of all web service endpoints to identify similar access control bypass vulnerabilities that could exist in other parts of the system.