CVE-2020-13671 in Drupal
Summary
by MITRE • 11/21/2020
Drupal core does not properly sanitize certain filenames on uploaded files, which can lead to files being interpreted as the incorrect extension and served as the wrong MIME type or executed as PHP for certain hosting configurations. This issue affects: Drupal Drupal Core 9.0 versions prior to 9.0.8, 8.9 versions prior to 8.9.9, 8.8 versions prior to 8.8.11, and 7 versions prior to 7.74.
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Analysis
by VulDB Data Team • 09/09/2024
Drupal core contains a critical file upload sanitization vulnerability that stems from inadequate filename validation during file processing. The flaw allows malicious actors to manipulate file extensions in ways that can bypass security controls and potentially execute arbitrary code on vulnerable systems. This vulnerability specifically impacts Drupal installations running versions prior to the mentioned patches, creating a persistent risk across multiple major versions including the widely used 7.x, 8.x, and 9.x release lines. The sanitization failure occurs when the system processes uploaded files, particularly those with multiple extensions or unusual filename formats that may be interpreted by web servers or application logic in unexpected ways.
The technical implementation of this vulnerability relies on the improper handling of filename parsing and extension validation within Drupal's file management subsystem. When files are uploaded, the system should normalize and sanitize filenames to prevent malicious manipulation, but the flaw allows certain characters or extension patterns to pass through without proper validation. This can result in files being interpreted with incorrect MIME types, where a file with a .php extension might be treated as an image or other non-executable format, or conversely, a file that should be treated as a static asset might be executed as PHP code. The vulnerability is particularly dangerous because it can be exploited in environments where web servers are configured to execute PHP files even when they appear to be static assets, creating a potential code execution vector.
The operational impact of this vulnerability extends beyond simple file upload restrictions and can lead to complete system compromise when exploited. Attackers can upload malicious files that, depending on server configuration, may be executed as PHP scripts, potentially allowing for remote code execution, data exfiltration, or further lateral movement within the network. The vulnerability affects not only the immediate file upload functionality but also broader security controls within the Drupal core, as it undermines the fundamental principle of input validation and sanitization. Organizations running affected Drupal versions face significant risk of unauthorized access, data breaches, and potential complete system compromise, particularly in environments where Drupal is used for content management, user authentication, or other critical functions.
The vulnerability aligns with CWE-77: Improper Neutralization of Special Elements used in a Command, which addresses the improper handling of special characters in input validation, and CWE-120: Buffer Copy without Checking Size of Input, which relates to improper handling of input data that can lead to execution of malicious code. From an ATT&CK framework perspective, this vulnerability maps to T1190: Exploit Public-Facing Application, as it represents a common attack vector through web application interfaces, and T1059: Command and Scripting Interpreter, which covers the execution of code through manipulated file uploads. Organizations should immediately implement the official patches released by Drupal for versions 7.74, 8.8.11, 8.9.9, and 9.0.8, while also implementing additional mitigations such as restricting file upload capabilities, implementing proper file type validation at multiple layers, and monitoring for suspicious file upload activities. Network segmentation and web application firewalls can provide additional defense in depth, though the primary solution remains the timely application of the vendor-provided security patches.