CVE-2021-24311 in External Media Plugin
Summary
by MITRE • 06/02/2021
The wp_ajax_upload-remote-file AJAX action of the External Media WordPress plugin before 1.0.34 was vulnerable to arbitrary file uploads via any authenticated users.
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Analysis
by VulDB Data Team • 06/03/2021
The vulnerability identified as CVE-2021-24311 affects the External Media WordPress plugin, specifically targeting the wp_ajax_upload-remote-file AJAX action. This flaw exists in versions prior to 1.0.34 and represents a critical security weakness that allows authenticated users to execute arbitrary file uploads on vulnerable systems. The issue stems from insufficient input validation and access control measures within the plugin's remote file upload functionality, creating a pathway for malicious actors to potentially compromise WordPress installations through unauthorized file operations.
The technical implementation of this vulnerability involves the wp_ajax_upload-remote-file endpoint which handles remote file upload requests through WordPress's AJAX system. When authenticated users interact with this endpoint, the plugin fails to properly validate file types, file contents, or destination paths before processing uploads. This lack of proper sanitization and validation creates an opportunity for attackers to upload malicious files such as web shells, malware, or other harmful content. The vulnerability is particularly concerning because it does not require administrative privileges, meaning any authenticated user account within the WordPress system can exploit this flaw.
The operational impact of CVE-2021-24311 extends beyond simple unauthorized file uploads, potentially enabling full system compromise through a chain of exploitation techniques. Attackers can leverage this vulnerability to upload web shells or other malicious scripts that provide persistent access to the compromised WordPress installation. The vulnerability aligns with CWE-434 which describes "Unrestricted Upload of File with Dangerous Type" and represents a clear violation of secure coding practices. This flaw can be categorized under ATT&CK technique T1190 "Exploit Public-Facing Application" and T1078 "Valid Accounts" since it exploits authenticated access to perform unauthorized operations.
Mitigation strategies for this vulnerability require immediate action including updating the External Media plugin to version 1.0.34 or later, which contains the necessary patches to address the file upload validation issues. Organizations should also implement additional security measures such as restricting file upload capabilities, implementing strict file type validation, and monitoring for suspicious upload activities. Network-based solutions including web application firewalls and intrusion detection systems can help detect and prevent exploitation attempts. Regular security audits and vulnerability assessments should be conducted to identify similar issues in other plugins and themes. The vulnerability demonstrates the importance of proper access control implementation and input validation in web applications, particularly those handling user-provided data through AJAX interfaces.