CVE-2017-6928 in Drupal
Summary
by MITRE
Drupal core 7.x versions before 7.57 when using Drupal's private file system, Drupal will check to make sure a user has access to a file before allowing the user to view or download it. This check fails under certain conditions in which one module is trying to grant access to the file and another is trying to deny it, leading to an access bypass vulnerability. This vulnerability is mitigated by the fact that it only occurs for unusual site configurations.
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Analysis
by VulDB Data Team • 02/10/2023
The vulnerability identified as CVE-2017-6928 represents a critical access control flaw within Drupal core version 7.x prior to 7.57 when utilizing the private file system functionality. This issue stems from a fundamental weakness in the permission checking mechanism that governs file access within the Drupal framework, specifically affecting scenarios where multiple modules attempt to simultaneously manage file access permissions. The flaw manifests when one module attempts to grant access to a file while another module simultaneously tries to deny access, creating a conflict in the permission resolution process that ultimately allows unauthorized users to bypass intended access controls.
The technical implementation of this vulnerability resides in the core permission checking logic within Drupal's file system handling components, which operates under the Common Weakness Enumeration classification of CWE-284 Access Control. This weakness specifically manifests when the system fails to properly evaluate conflicting access control decisions from different modules, resulting in a scenario where the access control system becomes inconsistent and unreliable. The vulnerability exploits the lack of proper synchronization or prioritization mechanisms in the permission evaluation process, allowing the system to potentially grant access based on incomplete or conflicting permission states.
From an operational impact perspective, this vulnerability creates a significant security risk for Drupal installations that rely on the private file system for sensitive content protection. The access bypass allows unauthorized users to potentially download or view files that should be restricted to specific user roles or permissions, potentially exposing confidential data, user uploads, or system files. The risk is particularly concerning because it can be exploited without requiring elevated privileges or specific authentication credentials, making it a serious concern for organizations relying on Drupal for content management and file handling. The vulnerability's impact is further amplified when considering the ATT&CK framework's privilege escalation techniques, as unauthorized access to private files can lead to additional reconnaissance and exploitation opportunities.
The mitigation strategy for this vulnerability primarily involves upgrading to Drupal core version 7.57 or later, which includes the necessary patches to resolve the permission checking inconsistency. Organizations should also conduct thorough security audits of their current module configurations to identify potential conflicts between access control modules that might exacerbate the vulnerability. Additionally, implementing proper module dependency management and access control policies can help reduce the likelihood of conflicting permission decisions. Security teams should consider implementing network-level monitoring to detect unauthorized file access attempts and establish regular security assessments to identify potential configuration issues that could lead to similar access control vulnerabilities. The vulnerability's remediation aligns with industry best practices for maintaining secure software configurations and demonstrates the importance of keeping content management systems updated with the latest security patches.