CVE-2015-2271 in Moodle
Summary
by MITRE
tag/user.php in Moodle through 2.5.9, 2.6.x before 2.6.9, 2.7.x before 2.7.6, and 2.8.x before 2.8.4 does not consider the moodle/tag:flag capability before proceeding with a flaginappropriate action, which allows remote authenticated users to bypass intended access restrictions via the "Flag as inappropriate" feature.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 05/19/2022
The vulnerability identified as CVE-2015-2271 affects the Moodle learning management system and represents a significant authorization bypass flaw that undermines the platform's access control mechanisms. This issue exists in multiple versions of Moodle including 2.5.9 and earlier, 2.6.x versions before 2.6.9, 2.7.x versions before 2.7.6, and 2.8.x versions before 2.8.4. The core problem lies within the tag/user.php component which handles user tagging functionality within the system. The vulnerability specifically targets the moodle/tag:flag capability, which is a critical permission control mechanism designed to restrict who can flag content as inappropriate within the Moodle environment. When users attempt to flag content as inappropriate through the web interface, the system fails to properly validate whether the authenticated user possesses the necessary privileges to perform this action.
The technical implementation flaw stems from insufficient capability checking within the tag/user.php script. This script processes flaginappropriate actions without first verifying that the requesting user holds the appropriate moodle/tag:flag permission. This oversight creates a direct pathway for authenticated users to bypass intended access restrictions and perform actions they should not be authorized to execute. The vulnerability operates at the application logic level and represents a classic authorization bypass where the system assumes all authenticated users can perform certain actions without proper privilege verification. This flaw aligns with CWE-285, which addresses insufficient authorization issues in software applications, and demonstrates how missing permission checks can lead to unauthorized access to system features.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it allows malicious actors to manipulate content flagging mechanisms within Moodle. Attackers who can authenticate to the system can potentially flag content that they should not have access to flag, which could lead to abuse of the content moderation system. This could result in false flagging of legitimate content, disruption of educational activities, or even the exposure of sensitive information that should remain restricted. The vulnerability affects the integrity of the content management system's moderation features and undermines the trustworthiness of the flagging mechanism that is intended to maintain appropriate content standards within educational environments. The attack requires only authenticated access, making it particularly dangerous as it can be exploited by users with legitimate accounts who may have elevated privileges or by attackers who have gained access through other means.
Organizations using affected Moodle versions should prioritize immediate remediation through official patches provided by the Moodle development team. The vulnerability can be mitigated by upgrading to patched versions of Moodle where the moodle/tag:flag capability is properly enforced before flaginappropriate actions are processed. Security administrators should also implement additional monitoring of flagging activities to detect potential abuse of this functionality. The remediation process should include comprehensive testing to ensure that legitimate users retain appropriate access while unauthorized actions are properly blocked. This vulnerability highlights the critical importance of proper capability checking in web applications and demonstrates how seemingly minor oversights in access control logic can create significant security risks. The issue also relates to ATT&CK technique T1078 which covers legitimate credentials and access, as the vulnerability allows bypassing access controls using existing authenticated sessions rather than requiring additional credential compromise.