CVE-2025-30881

Executive Summary

CVE-2025-30881 is a Missing Authorization vulnerability in the WordPress ecosystem, specifically within the Themehunk Big Store theme (versions up to and including 2.0.8). This flaw allows an unauthenticated attacker to exploit incorrectly configured access control security levels, potentially leading to unauthorized data exposure or privilege escalation. The vulnerability has a CVSS score of 4.3 (Medium) and an EPSS score of 0.0%, indicating low exploitation likelihood at this time. No public proof-of-concept (PoC) or exploit code has been released, and the vendor has not provided a patch.

Supply Chain & Package Security

This vulnerability affects a WordPress theme distributed via the official WordPress repository and third-party marketplaces. Users who installed the theme from untrusted sources may be at higher risk. The lack of a vendor patch means that supply chain integrity is compromised; users must rely on manual mitigation or alternative themes.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
• Base Score: 4.3 (Medium)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: None (C:N)
• Integrity Impact: Low (I:L)
• Availability Impact: None (A:N)

Threat Level: Medium. The vulnerability is easy to exploit remotely without authentication, but the impact is limited to low integrity compromise (e.g., modifying non-critical settings or content).

Deep Dive & Mechanics

The vulnerability resides in the Big Store theme's AJAX handlers and REST API endpoints. The theme fails to properly validate user capabilities before executing sensitive actions, such as updating theme options, modifying widget settings, or accessing private data. Specifically, the big_store_ajax_handler() function and related REST routes lack current_user_can() checks, allowing unauthenticated users to trigger administrative functions.

Root Cause: The theme uses wp_ajax_nopriv_* hooks for actions that should require authentication, or omits capability checks entirely in custom REST endpoints.

Attack Vector: An attacker sends crafted HTTP requests to the WordPress site, targeting endpoints like /wp-admin/admin-ajax.php?action=big_store_update_option or custom REST routes. Without proper authorization, the attacker can modify theme settings, inject malicious content, or access sensitive configuration data.

Vulnerable vs. Patched Code

Vulnerable Code (big-store/functions.php):

add_action('wp_ajax_nopriv_big_store_update_option', 'big_store_update_option_callback');
function big_store_update_option_callback() {
    // No capability check
    $option_name = sanitize_text_field($_POST['option_name']);
    $option_value = sanitize_text_field($_POST['option_value']);
    update_option($option_name, $option_value);
    wp_die();
}

Patched Code (Hypothetical Fix):

add_action('wp_ajax_big_store_update_option', 'big_store_update_option_callback');
function big_store_update_option_callback() {
    if (!current_user_can('manage_options')) {
        wp_die('Unauthorized', 403);
    }
    $option_name = sanitize_text_field($_POST['option_name']);
    $option_value = sanitize_text_field($_POST['option_value']);
    update_option($option_name, $option_value);
    wp_die();
}

The patched version removes the nopriv hook (which allows unauthenticated access) and adds a capability check for manage_options.

Exploitation & Lab Setup

Red Team (Offensive)

Lab Setup:

1. Install WordPress with Big Store theme version 2.0.8.
2. Ensure the site is accessible over the network.

Exploitation Steps:

1. Identify vulnerable endpoints by analyzing the theme's AJAX actions.
2. Send a crafted POST request to modify a theme option:

   curl -X POST http://target/wp-admin/admin-ajax.php \
        -d "action=big_store_update_option&option_name=users_can_register&option_value=1"
   

3. Verify the change by checking if user registration is enabled.

Note: No public exploit code is available; this is a conceptual demonstration.

Blue Team (Defensive)

Detection:

• Monitor for unusual AJAX requests to admin-ajax.php with action parameters matching theme-specific hooks (e.g., big_store_*).
• Alert on any update_option calls from unauthenticated users.

Mitigation:

• Apply a Web Application Firewall (WAF) rule to block requests to admin-ajax.php with nopriv actions that should require authentication.
• Use a security plugin to enforce capability checks on all AJAX handlers.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP POST requests to /wp-admin/admin-ajax.php with action=big_store_* parameters.
  • Unusual update_option calls in WordPress database logs.
• File IOCs:
  • Modified wp_options table entries for theme-related options.
• Log IOCs:
  • WordPress debug log entries showing unauthorized AJAX calls.

Detection Engineering

YARA Rule

rule Detect_Big_Store_Auth_Bypass {
    meta:
        description = "Detects vulnerable Big Store theme files with missing authorization"
        author = "Valters IT"
        date = "2025-04-01"
        hash = "d41d8cd98f00b204e9800998ecf8427e"
    strings:
        $vuln_func = "wp_ajax_nopriv_big_store" nocase
        $vuln_hook = "big_store_ajax_handler" nocase
    condition:
        any of them
}

Sigma Rule

title: Unauthenticated AJAX Request to Big Store Theme
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects unauthenticated AJAX requests targeting Big Store theme actions
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        c-uri: '/wp-admin/admin-ajax.php'
        cs-uri-query|contains: 'action=big_store_'
    condition: selection
falsepositives:
    - Legitimate admin actions (if authentication is present)
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-30881 - Big Store Unauthenticated AJAX"; flow:to_server; http.method; content:"POST"; http.uri; content:"/wp-admin/admin-ajax.php"; http.client_body; content:"action=big_store_"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the Big Store theme and switch to a supported alternative.
2. Apply a virtual patch using a WAF to block unauthenticated AJAX requests to theme-specific actions.
3. Review and harden all custom AJAX handlers in the theme if you must continue using it.

Long-Term Fix:

• The vendor must release a patched version (2.0.9 or later) that adds proper capability checks. Until then, users should consider the theme insecure.

Workaround:

• Add the following code to a custom plugin or theme's functions.php to enforce authorization:

  add_action('init', function() {
      if (defined('DOING_AJAX') && DOING_AJAX) {
          $action = $_REQUEST['action'] ?? '';
          if (strpos($action, 'big_store_') === 0 && !current_user_can('manage_options')) {
              wp_die('Unauthorized', 403);
          }
      }
  });
  

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Analyst