CVE-2025-3776: WordPress TargetSMS Plugin RCE Vulnerability

CVE-2025-3776 Overview

The Verification SMS with TargetSMS plugin for WordPress contains a limited Remote Code Execution vulnerability affecting all versions up to and including 1.5. The vulnerability exists in the targetvr_ajax_handler function due to insufficient validation of callable function types. This security flaw allows unauthenticated attackers to execute arbitrary callable functions on vulnerable WordPress installations, potentially leading to information disclosure, system compromise, and further exploitation.

Critical Impact

Unauthenticated attackers can execute any callable PHP function on the WordPress site without authentication, enabling information disclosure through functions like phpinfo() and potential escalation to full system compromise.

Affected Products

• Verification SMS with TargetSMS WordPress Plugin version 1.5 and earlier
• WordPress installations running the vulnerable plugin versions

Discovery Timeline

• April 24, 2025 - CVE-2025-3776 published to NVD
• April 29, 2025 - Last updated in NVD database

Technical Details for CVE-2025-3776

Vulnerability Analysis

This vulnerability is classified as CWE-94 (Improper Control of Generation of Code / Code Injection). The core issue lies in the targetvr_ajax_handler function within the plugin's AJAX handling code, which fails to properly validate or restrict the types of functions that can be invoked through its interface.

The plugin exposes an AJAX endpoint that accepts user-controlled input to determine which PHP function to execute. Without proper allowlisting or validation of permitted functions, attackers can specify any PHP callable, including dangerous functions like phpinfo(), system(), or other functions that could lead to information disclosure or arbitrary command execution.

This represents a severe design flaw where user input is trusted to specify executable code paths. The lack of authentication requirements compounds the severity, as any external attacker can reach the vulnerable endpoint without credentials.

Root Cause

The root cause is insufficient input validation in the targetvr_ajax_handler function located in inc/ajax.php. The function accepts a user-supplied parameter that specifies which function to call but does not implement an allowlist of permitted functions or validate that the requested function is appropriate for the context. This violates the principle of least privilege and secure coding practices that require strict validation of any input that influences code execution flow.

Attack Vector

The attack is network-accessible and requires no authentication, making it trivially exploitable by remote attackers. An attacker can craft a malicious HTTP request to the WordPress AJAX handler (admin-ajax.php) with specially crafted parameters that instruct the vulnerable handler to execute arbitrary PHP callable functions.

The exploitation flow involves:

1. Sending a POST request to the WordPress AJAX endpoint
2. Specifying the vulnerable action handler (targetvr_ajax_handler)
3. Including a parameter that names the target PHP function to execute
4. The plugin executes the specified function without validation

While described as "limited" RCE due to constraints on passing arguments to the called functions, even the ability to call functions like phpinfo() can leak sensitive configuration details. More dangerous functions could potentially be called depending on the PHP environment configuration and available extensions.

For technical details, see the vulnerable code in the WordPress Plugin Trac and the Wordfence Vulnerability Report.

Detection Methods for CVE-2025-3776

Indicators of Compromise

• Unusual POST requests to admin-ajax.php with action=targetvr_ajax_handler parameter
• Unexpected function calls in PHP logs, particularly phpinfo() or system-related functions
• Access logs showing repeated AJAX requests from unknown IP addresses targeting the plugin endpoint
• Evidence of information disclosure through exposed phpinfo() output

Detection Strategies

• Monitor web server access logs for requests to admin-ajax.php containing suspicious action parameters related to the TargetSMS plugin
• Implement Web Application Firewall (WAF) rules to detect and block requests attempting to invoke arbitrary PHP functions through AJAX handlers
• Deploy intrusion detection signatures for POST requests targeting WordPress AJAX endpoints with code injection patterns
• Enable PHP error logging to capture unexpected function call attempts

Monitoring Recommendations

• Configure alerts for any POST requests to admin-ajax.php with targetvr related action parameters from external IP addresses
• Implement real-time monitoring of WordPress plugin activity logs for anomalous behavior
• Review web server logs periodically for patterns indicating exploitation attempts against AJAX endpoints
• Monitor for creation of new files or unexpected configuration changes that could indicate post-exploitation activity

How to Mitigate CVE-2025-3776

Immediate Actions Required

• Immediately disable or remove the Verification SMS with TargetSMS plugin if running version 1.5 or earlier
• Review web server logs for any signs of exploitation attempts targeting the vulnerable endpoint
• If exploitation is suspected, conduct a full security audit of the WordPress installation
• Consider implementing a WAF rule to block requests to the vulnerable AJAX action as a temporary measure

Patch Information

At the time of publication, users should check the WordPress Plugin Repository for updated versions that address this vulnerability. If no patched version is available, the plugin should be removed entirely until a security fix is released.

Workarounds

• Disable the Verification SMS with TargetSMS plugin until a patched version is available
• Implement WAF rules to block POST requests containing the vulnerable action parameter
• Restrict access to admin-ajax.php for unauthenticated users if the plugin functionality is not required for public users
• Consider using alternative SMS verification plugins that have been security audited

# Example .htaccess rule to block requests to vulnerable endpoint
<IfModule mod_rewrite.c>
  RewriteEngine On
  RewriteCond %{REQUEST_METHOD} POST
  RewriteCond %{QUERY_STRING} action=targetvr_ajax_handler [NC,OR]
  RewriteCond %{REQUEST_BODY} action=targetvr_ajax_handler [NC]
  RewriteRule ^wp-admin/admin-ajax\.php$ - [F,L]
</IfModule>