CVE-2013-5738 in WordPress
Summary
by MITRE
The get_allowed_mime_types function in wp-includes/functions.php in WordPress before 3.6.1 does not require the unfiltered_html capability for uploads of .htm and .html files, which might make it easier for remote authenticated users to conduct cross-site scripting (XSS) attacks via a crafted file.
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Analysis
by VulDB Data Team • 05/24/2021
The vulnerability described in CVE-2013-5738 represents a critical security flaw in WordPress core functionality that directly impacts content management system security. This issue affects WordPress versions prior to 3.6.1 and specifically targets the get_allowed_mime_types function located within the wp-includes/functions.php file. The vulnerability stems from insufficient capability checks during file upload validation processes, creating a pathway for malicious actors to exploit the system's trust model. The flaw particularly affects .htm and .html file extensions, which are commonly used for web content but can contain malicious scripts when improperly handled during upload operations.
The technical implementation of this vulnerability involves a capability validation bypass that allows authenticated users to upload HTML files without requiring the unfiltered_html capability that should normally be enforced for such file types. This occurs because the get_allowed_mime_types function fails to properly validate user permissions before permitting HTML file uploads, creating a scenario where users with lower privileges can potentially upload malicious content that could execute in the context of other users' browsers. The function's logic does not adequately differentiate between trusted and untrusted upload contexts, leading to inconsistent security controls across different user roles within the WordPress ecosystem. This represents a direct violation of the principle of least privilege and proper access control enforcement.
The operational impact of this vulnerability extends beyond simple file upload capabilities and creates significant risks for WordPress installations. Remote authenticated users can leverage this weakness to conduct cross-site scripting attacks by uploading carefully crafted HTML files that contain malicious javascript payloads. These payloads can execute in the browser context of other users who view the uploaded content, potentially leading to session hijacking, data theft, or further system compromise. The vulnerability is particularly dangerous because it operates within the legitimate file upload mechanisms that administrators expect to be secure, making it harder to detect and prevent. This type of vulnerability aligns with CWE-20, which addresses improper input validation, and specifically relates to CWE-79, which covers cross-site scripting flaws in web applications. The attack vector follows patterns consistent with ATT&CK technique T1566, specifically T1566.001 for credential access through malicious file uploads.
The security implications of this vulnerability demonstrate the critical importance of proper capability enforcement and input validation in content management systems. WordPress administrators who fail to update to version 3.6.1 or later remain exposed to potential exploitation by attackers who can leverage this flaw to gain unauthorized access to user sessions and execute arbitrary code within victim browsers. The vulnerability also highlights the broader challenge of maintaining security in complex web applications where multiple permission levels and upload mechanisms must be carefully coordinated. Organizations should implement immediate mitigations including mandatory updates to WordPress 3.6.1 or later, along with monitoring for suspicious file uploads and user behavior. Additionally, administrators should consider implementing additional security measures such as file type restrictions, content scanning, and network-based intrusion detection systems to provide defense-in-depth against similar vulnerabilities that may exist in other components of the web application stack.