CVE-2018-14028 in WordPress
Summary
by MITRE
In WordPress 4.9.7, plugins uploaded via the admin area are not verified as being ZIP files. This allows for PHP files to be uploaded. Once a PHP file is uploaded, the plugin extraction fails, but the PHP file remains in a predictable wp-content/uploads location, allowing for an attacker to then execute the file. This represents a security risk in limited scenarios where an attacker (who does have the required capabilities for plugin uploads) cannot simply place arbitrary PHP code into a valid plugin ZIP file and upload that plugin, because a machine's wp-content/plugins directory permissions were set up to block all new plugins.
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Analysis
by VulDB Data Team • 05/01/2023
The vulnerability described in CVE-2018-14028 represents a critical security flaw in WordPress version 4.9.7 that stems from inadequate validation of plugin upload processes within the administrative interface. This issue manifests when users with appropriate privileges attempt to upload plugins through the WordPress admin area, creating a potential attack vector that could be exploited by malicious actors. The vulnerability is particularly concerning because it operates under the assumption that attackers already possess the capability to upload plugins, which typically requires administrative access or equivalent privileges within the WordPress environment.
The technical flaw occurs due to insufficient verification mechanisms that should validate uploaded files as legitimate ZIP archives before processing them. When a user uploads what appears to be a plugin file, WordPress fails to properly validate the file format, allowing malicious actors to upload PHP files directly rather than conforming to the expected ZIP structure. This validation failure creates a scenario where PHP code can be embedded within what appears to be a legitimate plugin upload, bypassing normal security controls that would otherwise prevent such execution. The vulnerability is categorized under CWE-502 as "Deserialization of Untrusted Data" and relates to improper input validation and file format handling within web applications.
The operational impact of this vulnerability extends beyond simple file upload capabilities, creating a persistent threat vector that can be exploited even when standard plugin installation methods are blocked. When a PHP file is uploaded through this vulnerability, the plugin extraction process fails as expected, but the malicious PHP file is left in a predictable location within the wp-content/uploads directory. This predictable path allows attackers to execute the uploaded PHP code directly, effectively bypassing the normal plugin installation security measures. The vulnerability is particularly dangerous in environments where the wp-content/plugins directory has restrictive permissions that prevent new plugin installations, as it provides an alternative attack method that doesn't rely on the traditional plugin installation process.
The security implications of this vulnerability align with ATT&CK technique T1190 "Exploit Public-Facing Application" and T1059.007 "Command and Scripting Interpreter: PHP," as it enables attackers to execute arbitrary PHP code on compromised WordPress installations. The vulnerability demonstrates how inadequate input validation can create persistent backdoors within web applications, allowing attackers to maintain access and execute commands without requiring additional privileges. Organizations using WordPress 4.9.7 should consider this vulnerability as a critical risk, especially in environments where administrative access is a concern, as it essentially creates a bypass mechanism for executing arbitrary code that could be used for data exfiltration, system compromise, or further network penetration. The vulnerability also highlights the importance of proper file validation and the principle of least privilege in web application security.
Mitigation strategies should focus on immediate patching of WordPress installations to versions that address this vulnerability, along with implementing additional security controls such as file type validation, upload directory restrictions, and proper permission management. Organizations should also consider implementing web application firewalls, regular security audits, and monitoring for suspicious file uploads. The vulnerability underscores the need for comprehensive input validation and the importance of not relying solely on file extension checks, as attackers can exploit these validation gaps to bypass security controls. Regular security assessments and updates are essential to prevent exploitation of similar vulnerabilities that may exist in other parts of the WordPress ecosystem or related applications.