CVE-2018-1135 in Moodle
Summary
by MITRE
An issue was discovered in Moodle 3.x. Students who posted on forums and exported the posts to portfolios can download any stored Moodle file by changing the download URL.
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Analysis
by VulDB Data Team • 02/08/2020
This vulnerability exists within Moodle version 3.x platforms where users can export forum posts to portfolios. The flaw stems from insufficient access control validation during file download operations, allowing authenticated users to manipulate download URLs and gain unauthorized access to files they should not be able to retrieve. The vulnerability specifically affects the portfolio export functionality where forum posts are archived and made available for download. When students export forum posts to portfolios, the system generates download URLs that do not properly verify whether the requesting user has appropriate permissions to access the target file. This represents a classic privilege escalation issue where users can leverage their legitimate access to portfolio exports to obtain unauthorized file access. The vulnerability enables arbitrary file download attacks that could potentially expose sensitive course materials, personal documents, or other confidential information stored within the Moodle system. The flaw demonstrates a lack of proper input validation and access control mechanisms in the portfolio download component, creating an attack vector that bypasses normal file permission checks.
The technical implementation of this vulnerability occurs within the portfolio export module where download URLs are constructed without adequate authorization verification. When a user requests to download a file through the portfolio system, the application fails to validate whether the user has legitimate access rights to the specific file being requested. This allows an attacker to modify the download URL parameters to point to files they should not normally be able to access, effectively bypassing the system's file access controls. The vulnerability can be exploited through simple URL manipulation techniques where attackers modify the file identifiers in the download URLs to reference other files within the Moodle file storage system. This type of vulnerability aligns with CWE-284 Access Control Issues, specifically targeting improper access control mechanisms in web applications. The flaw also relates to the ATT&CK technique T1078 Valid Accounts, as it leverages legitimate user credentials to access unauthorized resources within the system.
The operational impact of this vulnerability is significant for educational institutions relying on Moodle platforms, as it creates potential data exposure risks that could compromise student privacy and institutional information security. Attackers could potentially access course materials, assignment submissions, personal documents, or other sensitive files that were not intended for public or unauthorized access. The vulnerability affects the core functionality of the portfolio system and could lead to unauthorized data exfiltration, particularly in environments where Moodle is used for sensitive academic or research activities. Organizations may experience compliance violations if student or institutional data is accessed without proper authorization. The ease of exploitation through simple URL manipulation means that even less technical attackers could potentially exploit this vulnerability, making it particularly concerning for widespread deployment environments. The impact extends beyond individual file access to potentially expose entire file directories or collections of related documents that share similar access patterns within the Moodle file structure.
Organizations should implement immediate mitigations including updating to patched versions of Moodle where this vulnerability has been addressed through proper access control enforcement. The fix typically involves implementing robust input validation and authorization checks within the portfolio download functionality to ensure that all file access requests are properly authenticated and authorized. Administrators should review and tighten file access permissions within Moodle to limit what users can access through portfolio exports, particularly for sensitive course materials or personal files. Network monitoring should be enhanced to detect unusual download patterns or attempts to access files outside of normal user behavior. Regular security audits should verify that access controls are properly enforced throughout the portfolio system and that no similar access control bypass vulnerabilities exist in other components. Implementing additional logging and monitoring around portfolio export and download activities can help detect potential exploitation attempts. Security awareness training for users about proper file sharing practices and the risks of sharing portfolio export links can also reduce the attack surface. Organizations should also consider implementing web application firewalls or additional access control layers to provide defense-in-depth against similar vulnerabilities. The mitigation approach should align with security best practices for access control as outlined in NIST SP 800-53 and ISO 27001 standards to ensure comprehensive protection against unauthorized file access scenarios.