CVE-2018-20149 in WordPress
Summary
by MITRE
In WordPress versions before 5.0.1, when the Apache HTTP Server is used, authors could upload crafted files that bypass intended MIME type restrictions, leading to XSS.
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Analysis
by VulDB Data Team • 06/19/2023
The vulnerability identified as CVE-2018-20149 represents a critical security flaw in WordPress versions prior to 5.0.1 that specifically affects installations using the Apache HTTP Server. This issue stems from inadequate MIME type validation mechanisms that allow malicious actors to upload files with deceptive extensions while maintaining executable content. The flaw occurs at the server-level file handling process where Apache's configuration permits certain file types to be processed without proper MIME type verification, creating an exploitable gap in WordPress's security architecture.
The technical implementation of this vulnerability exploits the interaction between WordPress's file upload system and Apache's content handling capabilities. When users with author privileges attempt to upload files, the system relies on Apache's default MIME type detection rather than implementing robust validation checks. Attackers can craft files with extensions like .jpg or .png that actually contain malicious javascript code or other executable content. This bypasses WordPress's intended security measures that would normally reject such files based on their actual content rather than their file extension. The vulnerability specifically targets the Apache server configuration where certain file types are processed without proper MIME type validation, allowing malicious payloads to be executed in the context of the victim's browser.
The operational impact of this vulnerability is significant as it enables cross-site scripting attacks through seemingly benign file uploads. An attacker with author privileges can upload malicious files that, when accessed by other users, execute javascript code in their browser sessions. This creates potential for session hijacking, data theft, and further exploitation within the WordPress environment. The vulnerability essentially transforms the file upload functionality from a legitimate feature into a vector for executing arbitrary code, undermining the security model of the content management system. The attack surface extends beyond simple XSS to potentially enable privilege escalation and persistent threats within the WordPress installation.
This vulnerability aligns with CWE-434, which describes the weakness of unrestricted file upload, and relates to ATT&CK technique T1190 for Exploit Public-Facing Application. The flaw demonstrates poor input validation and insufficient server-side file type verification, creating an environment where malicious files can bypass security controls. Organizations should implement immediate mitigations including updating to WordPress 5.0.1 or later, configuring Apache to enforce stricter MIME type validation, and implementing additional file content checks beyond simple extension validation. Network monitoring should be enhanced to detect unusual file upload patterns, and user privilege management should be reviewed to limit upload capabilities to trusted administrators only. The vulnerability underscores the importance of comprehensive security testing and validation of server configurations in web application environments.