Exploitation Research Plan: CVE-2026-1675 - Advanced Country Blocker Authorization Bypass

1. Vulnerability Summary

The Advanced Country Blocker plugin (<= 2.3.1) contains an unauthenticated authorization bypass vulnerability. The plugin provides a "Secret Bypass Key" feature intended to allow specific users (e.g., administrators or testers) to bypass geolocation-based blocking by appending a specific key to the URL.

The vulnerability arises because the plugin initializes this secret key with a predictable default value (e.g., 1234567890) upon installation and does not mandate a change. Consequently, if an administrator enables country blocking but leaves the default secret key unchanged, any unauthenticated user can bypass the restrictions by including the default key in a GET request.

2. Attack Vector Analysis

• Endpoint: Any public-facing URL on the WordPress site.
• Vulnerable Parameter: A GET parameter (inferred as acb_key or bypass_key) used to provide the secret value.
• Payload: The default secret key value (inferred as 1234567890 or acb_secret).
• Authentication: None required (Unauthenticated).
• Preconditions:
  1. The plugin must be active.
  2. Country blocking must be enabled for the attacker's region.
  3. The "Secret Bypass Key" setting must be at its default value.

3. Code Flow (Inferred)

1. Initialization: During plugin initialization (via init or plugins_loaded hook), the plugin checks the visitor's IP address against the configured blocked countries.
2. Bypass Check: Before executing the blocking logic (e.g., wp_die() or redirecting to a "Blocked" page), the plugin checks for a bypass key in the request:

   // Example logic in advanced-country-blocker.php
   $settings = get_option('acb_settings');
   $bypass_key = $settings['bypass_key']; // Default: '1234567890'
   
   if (isset($_GET['acb_key']) && $_GET['acb_key'] === $bypass_key) {
       // Set a cookie or session to allow access
       setcookie('acb_bypass', 'true', ...);
       return; // Exit blocking logic early
   }
   

3. Sink: If the bypass condition is NOT met and the country is blocked, the plugin triggers the block sink (e.g., a custom error page). If the bypass IS met, the normal page execution continues.

4. Nonce Acquisition Strategy

This vulnerability does not require a nonce. The bypass mechanism is designed to work via a direct URL link (often sent in emails or used for testing), and therefore relies on a static secret key rather than a transient WordPress CSRF nonce.

5. Exploitation Strategy

The goal is to demonstrate that a blocked visitor can access the site using the default key.

Step 1: Discovery of Identifiers

The agent must first identify the exact parameter name and default value from the source.

1. Search for the bypass check: grep -rn "\$_GET" . in the plugin directory.
2. Look for where the key is retrieved from options: grep -rn "get_option" ..
3. Look for the default value in the activation hook: grep -rn "register_activation_hook" . or search for the string 1234567890.

Inferred Values for Plan:

• Parameter Name: acb_key
• Default Value: 1234567890

Step 2: Triggering the Bypass

1. Establish a Block: Configure the plugin to block the current environment's IP/Country.
2. Verify Block: Attempt to access the homepage.
   • Request: GET /
   • Expected Response: A "Blocked" message or a 403 status.
3. Execute Bypass: Access the homepage with the bypass parameter.
   • Request: GET /?acb_key=1234567890
   • Expected Response: HTTP 200 OK with the actual homepage content.

6. Test Data Setup

To reliably reproduce the vulnerability in an automated environment:

1. Install/Activate: Ensure advanced-country-blocker version 2.3.1 is installed.
2. Configuration via WP-CLI:

   # Enable blocking and set a rule that blocks the attacker
   # This might require simulating a specific country or blocking the 'all' category
   wp option update acb_settings '{"status":"on", "blocked_countries":["ALL"], "bypass_key":"1234567890"}' --format=json
   

   (Note: The exact structure of acb_settings should be verified by the agent via wp option get acb_settings first.)

7. Expected Results

• Without Key: The HTTP response should contain text indicating access is denied (e.g., "Your country is blocked" or "Access Denied").
• With Key: The HTTP response should contain the standard WordPress site content (e.g., <div id="page"> or the site's title).
• Cookie Setting: The plugin may set a bypass cookie upon successful key verification, allowing subsequent requests without the parameter to also succeed.

8. Verification Steps

1. HTTP Check: Verify the http_request for /?acb_key=1234567890 returns a 200 status and does not contain the "Blocked" string.
2. Settings Check: Use WP-CLI to confirm the secret key in the database matches the one used in the exploit:

   wp option get acb_settings
   

3. Log Check: If the plugin logs blocked attempts, verify that the bypass attempt was either not logged or logged as a bypass event.

9. Alternative Approaches

• Cookie-based Bypass: If the plugin uses a cookie after the first successful bypass, verify the bypass by:
  1. Sending the request with the key.
  2. Extracting the Set-Cookie header.
  3. Sending a second request without the key but with the cookie to confirm persistent access.
• Parameter Guessing: If the parameter is not acb_key, common alternatives include bypass, acb_bypass, or secret. These can be identified by searching for $_GET or $_REQUEST in the plugin source.
• Default Key Variants: If 1234567890 fails, common default keys to check in the source include:
  • 12345
  • bypass
  • Empty string (if the check is $_GET['key'] == $val and $val is uninitialized).
  • The site name or plugin slug.