Executive Summary

CVE-2019-25738 is a critical vulnerability in the WordPress Hybrid Composer plugin version 1.4.6 and earlier. It allows unauthenticated attackers to modify WordPress settings by exploiting the hc_ajax_save_option action. Attackers can send specially crafted POST requests to the admin-ajax.php endpoint with the action parameter set to hc_ajax_save_option, which lets them change options such as enabling user registration and setting the default user role to administrator.

This vulnerability arises because the plugin exposes a non-private AJAX hook (wp_ajax_nopriv_hc_ajax_save_option) that does not require authentication, allowing attackers to update arbitrary options in the WordPress database without any access control.

As a result, attackers can create new administrator accounts and take over the WordPress site completely.

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Compliance Impact

The vulnerability allows unauthenticated attackers to modify WordPress options, including enabling user registration and setting the default role to administrator, which can lead to account takeover and complete system compromise.

Such unauthorized access and control over a website could lead to violations of common standards and regulations like GDPR and HIPAA, as attackers may gain access to sensitive personal data or protected health information by exploiting this vulnerability.

Therefore, this vulnerability poses a significant risk to compliance with data protection and privacy regulations by potentially enabling unauthorized data access and manipulation.

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Impact Analysis

This vulnerability can have severe impacts including complete site takeover. By exploiting it, attackers can enable user registration and assign the administrator role to new users, effectively granting themselves full administrative access.

Once an attacker gains administrator privileges, they can control the website, modify content, install malicious plugins or backdoors, steal sensitive data, and disrupt normal operations.

Because the vulnerability requires no authentication and can be exploited remotely, it poses a high risk of compromise for affected WordPress sites.

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Detection Guidance

This vulnerability can be detected by monitoring for unauthorized POST requests to the WordPress admin-ajax.php endpoint with the action parameter set to hc_ajax_save_option. Such requests indicate attempts to exploit the unauthenticated settings change flaw.

To detect exploitation attempts on your system, you can use network monitoring or web server logs to search for POST requests like the following:

• Using grep on web server logs: grep "POST /wp-admin/admin-ajax.php" /var/log/apache2/access.log | grep "action=hc_ajax_save_option"
• Using tcpdump to capture such requests: tcpdump -A -s 0 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' | grep "hc_ajax_save_option"

Additionally, checking the WordPress options table for unexpected changes such as enabled user registration or default role set to administrator can help detect if the vulnerability has been exploited.

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Mitigation Strategies

The immediate mitigation step is to update the WordPress Hybrid Composer plugin to a version later than 1.4.6 where this vulnerability has been patched.

If updating immediately is not possible, temporarily disabling the Hybrid Composer plugin or restricting access to the admin-ajax.php endpoint to authenticated users can reduce the risk.

Additionally, review and reset WordPress settings to disable user registration and verify that the default user role is not set to administrator to prevent unauthorized account creation.

Monitoring logs for suspicious POST requests to admin-ajax.php with the vulnerable action parameter and changing WordPress administrator passwords are also recommended.

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