CVE-2016-6635 in WordPress
Summary
by MITRE
Cross-site request forgery (CSRF) vulnerability in the wp_ajax_wp_compression_test function in wp-admin/includes/ajax-actions.php in WordPress before 4.5 allows remote attackers to hijack the authentication of administrators for requests that change the script compression option.
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Analysis
by VulDB Data Team • 09/13/2022
The CVE-2016-6635 vulnerability represents a critical cross-site request forgery flaw within the WordPress content management system that specifically targets the administrative interface. This vulnerability exists in the wp_ajax_wp_compression_test function located in the wp-admin/includes/ajax-actions.php file, affecting all WordPress installations prior to version 4.5. The flaw enables remote attackers to manipulate administrator sessions by crafting malicious requests that alter script compression settings, effectively allowing unauthorized modification of critical system configurations. The vulnerability stems from the absence of proper authentication verification mechanisms within the AJAX handling function, creating a pathway for attackers to execute unauthorized administrative actions without legitimate credentials.
The technical implementation of this CSRF vulnerability exploits the trust relationship between the WordPress administrative interface and legitimate AJAX requests. When administrators access the WordPress admin panel, their session remains active and authenticated, but the wp_ajax_wp_compression_test function fails to validate the authenticity of incoming requests through proper nonce verification or session token validation. This oversight allows attackers to construct malicious web pages or emails containing embedded requests that, when clicked by an authenticated administrator, automatically execute the compression option change without requiring additional authentication. The vulnerability specifically targets the script compression feature which can significantly impact website performance and security posture, as compression settings directly affect how JavaScript and CSS files are delivered to users.
The operational impact of CVE-2016-6635 extends beyond simple configuration changes, as script compression settings can influence website performance, security, and user experience. An attacker who successfully exploits this vulnerability could potentially degrade website performance by disabling compression, increase bandwidth usage, or even introduce security risks by modifying how assets are served. The attack vector typically involves social engineering techniques where administrators are tricked into visiting malicious websites or clicking on compromised links that contain embedded CSRF payloads. This vulnerability aligns with CWE-352, which specifically addresses Cross-Site Request Forgery issues, and demonstrates the critical importance of implementing proper request validation and authentication mechanisms in web applications. The flaw also maps to ATT&CK technique T1078.004, which covers valid accounts used for persistence and privilege escalation.
Mitigation strategies for this vulnerability require immediate patching of WordPress installations to version 4.5 or later, where the CSRF protection mechanisms have been properly implemented. Organizations should also implement additional security measures including the use of security headers, content security policies, and regular security audits of WordPress installations. Network administrators should monitor for suspicious activity related to administrative AJAX requests and implement web application firewalls to detect and block malicious CSRF attempts. The vulnerability highlights the importance of following secure coding practices such as implementing proper nonce validation for all administrative functions and ensuring that AJAX handlers perform adequate authentication checks before executing sensitive operations. Regular security assessments and penetration testing should be conducted to identify similar vulnerabilities in custom WordPress themes and plugins that may not have received the same level of security scrutiny as core WordPress components.