CVE-2012-3387 in Moodle
Summary
by MITRE
Moodle 2.3.x before 2.3.1 uses only a client-side check for whether references are permitted in a file upload, which allows remote authenticated users to bypass intended alias (aka shortcut) restrictions via a client that omits this check.
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Analysis
by VulDB Data Team • 12/06/2021
The vulnerability identified as CVE-2012-3387 affects Moodle version 2.3.x before 2.3.1 and represents a critical security flaw in the file upload validation mechanism. This issue stems from the application's reliance on client-side validation for determining whether file references are permitted, creating a fundamental security weakness that can be exploited by authenticated attackers. The vulnerability specifically targets the alias or shortcut restrictions that Moodle implements to control file access and prevent unauthorized reference creation within the system.
The technical flaw manifests through the absence of proper server-side validation for file upload operations. When users attempt to upload files, Moodle's implementation only verifies permissions and restrictions on the client side, meaning that the security checks are performed in the browser rather than on the server. This client-side validation can be easily bypassed by attackers who manipulate their client-side requests to omit or alter the validation checks that would normally prevent unauthorized alias creation. The flaw essentially allows malicious actors to create symbolic links or shortcuts to files they should not have access to, effectively circumventing the intended access control mechanisms.
From an operational perspective, this vulnerability poses significant risks to organizations using Moodle as their learning management system. An authenticated attacker with access to the platform can exploit this weakness to gain unauthorized access to files that should be restricted, potentially leading to data exposure, information leakage, and privilege escalation. The impact extends beyond simple file access, as the ability to create unauthorized aliases can enable further attacks such as cross-site scripting attempts or privilege escalation within the system. This vulnerability undermines the core security model of Moodle's file management system and compromises the integrity of the access control mechanisms that protect sensitive educational content and user data.
The security implications of this vulnerability align with CWE-602, which addresses client-side enforcement of server-side security checks, and can be mapped to ATT&CK technique T1078 for valid accounts and T1566 for phishing attacks that might be used to obtain initial access. Organizations should implement immediate mitigations including upgrading to Moodle 2.3.1 or later versions where the server-side validation has been properly implemented. Additional protective measures include monitoring file upload activities, implementing network segmentation to limit access to the Moodle environment, and conducting regular security audits of file management systems. The vulnerability highlights the critical importance of server-side validation in web applications and serves as a reminder that client-side security checks alone are insufficient for protecting against determined attackers who can manipulate browser behavior to bypass such restrictions.