CVE-2016-2159 in Moodle
Summary
by MITRE
The save_submission function in mod/assign/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 allows remote authenticated users to bypass intended due-date restrictions by leveraging the student role for a web-service request.
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Analysis
by VulDB Data Team • 08/21/2022
The vulnerability identified as CVE-2016-2159 represents a significant security flaw in the Moodle learning management system that affects multiple version branches including 2.6.x through 2.6.11, 2.7.x through 2.7.12, 2.8.x through 2.8.10, 2.9.x through 2.9.4, and 3.0.x through 3.0.2. This issue stems from improper access control mechanisms within the assignment submission functionality, specifically within the save_submission function located in the mod/assign/externallib.php file. The flaw enables authenticated users with the student role to exploit web-service requests in ways that circumvent the intended due-date restrictions that protect assignment submissions. This vulnerability falls under the CWE-284 access control weakness category, specifically representing an improper access control scenario where the system fails to properly validate user permissions before allowing submission operations.
The technical implementation of this vulnerability occurs through the web-service interface that Moodle provides for external system integration and automated operations. When a student user makes a web-service request to submit an assignment through the save_submission function, the system should verify that the submission occurs within the designated due-date window for that particular assignment. However, the flaw allows malicious or unauthorized users to bypass this validation by leveraging their student role credentials in web-service requests. This bypass mechanism essentially removes the temporal constraints that normally govern assignment submissions, permitting users to submit work past the established deadlines without proper authorization. The vulnerability is particularly concerning because it operates at the application logic level where business rules for assignment management are enforced, and it demonstrates a clear failure in the principle of least privilege enforcement.
The operational impact of this vulnerability extends beyond simple grade manipulation and represents a fundamental breach in the academic integrity mechanisms that Moodle systems rely upon for managing student assignments. When exploited, this vulnerability allows students to submit assignments after the official due dates have passed, potentially enabling academic dishonesty through late submissions that could be accepted without proper oversight. This issue affects the core educational workflow where instructors establish due dates to manage student workload, enforce academic standards, and maintain proper assessment timelines. The vulnerability's exploitation requires only authenticated access with student privileges, making it particularly dangerous as it can be leveraged by any user who has gained access to a legitimate student account or by malicious actors who have compromised such credentials. Security practitioners should note that this vulnerability aligns with ATT&CK technique T1078 legitimate credentials, as it exploits existing user permissions to perform unauthorized actions.
Organizations running affected Moodle versions face significant risks including compromised academic integrity, potential grade manipulation, and disruption of normal educational workflows. The vulnerability's persistence across multiple version branches indicates a systemic issue in the codebase that required coordinated patching efforts across different release lines. System administrators should prioritize immediate patching of affected installations, particularly in environments where academic integrity is paramount. The recommended mitigations include applying the official security patches provided by Moodle for each affected version branch, implementing additional monitoring of web-service usage patterns, and considering the enforcement of more granular access controls for web-service endpoints. Security teams should also conduct thorough audits of web-service configurations and user permissions to ensure that similar access control bypasses do not exist in other components of the system. This vulnerability underscores the importance of proper input validation and access control enforcement in web applications, particularly those handling sensitive educational data and academic workflows.