Hackers Exploit Critical Post SMTP Plugin Bug to Hijack WordPress Sites

A serious vulnerability in the popular Post SMTP plugin, installed on over 400,000 WordPress sites, is now being actively exploited. WordFence reported that the Post SMTP plugin bug allows attackers to view sensitive email logs and even take full control of WordPress admin accounts.

Post SMTP plugin Actual Bug

Here’s what caused the issue:

• The Post SMTP plugin helps WordPress sites send and log outgoing emails such as password resets or form submissions.
• Versions up to 3.6.0 failed to check user permissions properly. This let anyone, even unauthenticated visitors, view logged emails by calling specific URLs.
• One dangerous result was exposure of password reset emails. Attackers could trigger a reset, retrieve it from the logs, and use the reset link to change the admin password, gaining complete access.
• The flaw has been identified as CVE-2025-11833 with a critical severity score of 9.8.

Impact of Post SMTP Plugin Bug

• More than 400,000 WordPress sites are affected worldwide.
• Security researchers have already confirmed active exploitation just days after the fix was released. Thousands of attacks have been detected and blocked.
• Since the exploit doesn’t require login credentials, any site running a vulnerable version is at immediate risk.

Technical Breakdown for Developers

Below is a simplified example of what went wrong in the plugin code, and how it should have been secured.

Vulnerable code:

public function __construct() {
 
    global $wpdb;
 
    $this->db = $wpdb;
    $this->logger = new PostmanLogger( get_class( $this ) );
 
    //Render Message body in iframe
    if(
        isset( $_GET['page'] ) && $_GET['page'] == 'postman_email_log'
        &&
        isset( $_GET['view'] ) && $_GET['view'] == 'log'
        &&
        isset( $_GET['log_id'] ) && !empty( $_GET['log_id'] )
    ) {
 
        // Print
        if( isset( $_GET['print'] ) && $_GET['print'] == 1  ) {
 
            echo "<script>window.print();</script>";
 
        }
 
        $id = sanitize_text_field( $_GET['log_id'] );
        $email_query_log = new PostmanEmailQueryLog();
        $log = $email_query_log->get_log( $id, '' );
        $header = $log['original_headers'];
        $msg = $log['original_message'];
        $msg = $this->purify_html( $msg );
        echo ( isset ( $header ) && strpos( $header, "text/html" ) ) ? $msg : '' . $msg . '' ;
 
        die;
 
    }

Why it failed:

• No check to confirm the user’s permissions or login status.
• Relied on $_GET without any nonce or security verification.
• Executed automatically inside the constructor, allowing easy abuse.

Secure version (simplified):

public function __construct() {
    global $wpdb;
    $this->db = $wpdb;

    if (
        isset($_GET['page']) && $_GET['page'] === 'postman_email_log'
        && isset($_GET['view']) && $_GET['view'] === 'log'
        && isset($_GET['log_id']) && ! empty($_GET['log_id'])
    ) {
        if ( ! current_user_can( 'manage_options' ) ) {
            wp_die( __( 'You do not have permission to access this page.', 'textdomain' ) );
        }

        if ( ! isset($_GET['_wpnonce']) || ! wp_verify_nonce( $_GET['_wpnonce'], 'view_email_log' ) ) {
            wp_die( __( 'Security check failed.', 'textdomain' ) );
        }

        $id = sanitize_text_field( $_GET['log_id'] );
        $email_query_log = new PostmanEmailQueryLog();
        $log = $email_query_log->get_log($id, '');
        echo esc_html( $log );
        die;
    }
}

Key lessons for WordPress developers:

• Always verify permissions using current_user_can().
• Use nonces with wp_verify_nonce() to prevent CSRF.
• Sanitize every input and escape every output.
• Avoid putting sensitive logic inside constructors.

What You Should Do Now

If you manage WordPress sites with Post SMTP Plugin, act quickly:

1. Update immediately: Go to your plugins list and make sure Post SMTP is version 3.6.1 or newer.
2. Change passwords: Assume that any admin credentials could be compromised if you used a vulnerable version.
3. Enable two-factor authentication: Add extra security for all admin users.
4. Clean up logs: Review and delete any sensitive email logs that may have been exposed.
5. Keep everything updated: Regularly update WordPress core, themes, and plugins.
6. Audit your code: Check all your plugins and themes for proper capability checks and nonce verification.
7. Document your security steps: Make this a regular part of your maintenance or client handover process.

Why It Matters

This isn’t just a plugin bug, it’s a wake-up call for WordPress site owners and developers.

For developers, it highlights the importance of secure coding practices and the risk of overlooking basic permission checks.

For bloggers and business owners, it’s a reminder that even one outdated plugin can expose your entire site. A hacked admin account can damage your brand, SEO, and community trust overnight.

Never overlook even the smallest security measure.

Final Thoughts

In this article, we also discussed the coding side of the Post SMTP security issue to help you understand why even the smallest security measure matters. Ignoring best practices in development can easily turn into a real-world threat. Remember, in this vast and ever-evolving digital space, there’s always someone ready to exploit a weak spot.

If you use Post SMTP, update it right now. The patch is live, and attackers are already taking advantage of the flaw.

Think of this as a reminder ,building a site is only half the job, protecting it is the other half. Stay alert, stay updated, and keep your WordPress sites safe.