CVE-2025-49884

Executive Summary

CVE-2025-49884 is a Missing Authorization vulnerability in the WordPress plugin Internal Linking of Related Contents by alexvtn. This flaw allows an unauthenticated attacker to exploit incorrectly configured access control security levels, potentially leading to unauthorized data access or modification. The vulnerability affects all versions up to and including 1.1.8. As of this report, no official patch has been released, and no public proof-of-concept (PoC) or exploit code is available. The EPSS score is 0.0%, indicating low exploitation likelihood currently, but the risk remains due to the unpatched state.

Supply Chain & Package Security

This vulnerability resides in a WordPress plugin ecosystem. WordPress plugins are distributed via the official WordPress Plugin Directory or third-party marketplaces. Users should verify the integrity of the plugin files by checking checksums or using trusted sources. Since no patch is available, the supply chain risk is elevated—users must rely on manual mitigation or plugin replacement.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – Vulnerability does not affect other components.
• Confidentiality (C): Low (L) – Limited data exposure.
• Integrity (I): Low (L) – Limited data modification.
• Availability (A): None (N) – No impact on availability.

CVSS Score: 6.5 (Medium) – The vulnerability is remotely exploitable without authentication, but impact is limited to low confidentiality and integrity.

Deep Dive & Mechanics

The vulnerability stems from missing authorization checks in the plugin's AJAX handlers or REST API endpoints. The plugin likely exposes functions to manage internal links without verifying user capabilities (e.g., edit_posts or manage_options). An attacker can send crafted HTTP requests to these endpoints to:

• Retrieve or modify internal linking configurations.
• Access or alter related content mappings.
• Potentially escalate privileges if combined with other flaws.

The core issue is that the plugin relies on client-side checks or insufficient server-side validation, allowing unauthenticated users to invoke privileged actions.

Vulnerable vs. Patched Code

Since no patch is available, we can only infer the vulnerable pattern. A typical missing authorization vulnerability in WordPress plugins looks like:

Vulnerable Code (PHP):

add_action('wp_ajax_nopriv_update_link', 'update_link_handler');
function update_link_handler() {
    // No capability check
    $post_id = $_POST['post_id'];
    update_post_meta($post_id, '_internal_link', $_POST['link_data']);
    wp_die();
}

Patched Code (Hypothetical):

add_action('wp_ajax_update_link', 'update_link_handler');
function update_link_handler() {
    if (!current_user_can('edit_posts')) {
        wp_die('Unauthorized', 403);
    }
    $post_id = intval($_POST['post_id']);
    update_post_meta($post_id, '_internal_link', sanitize_text_field($_POST['link_data']));
    wp_die();
}

The fix would involve adding capability checks (current_user_can()) and nonce verification to all AJAX endpoints.

Exploitation & Lab Setup

Red Team (Exploitation)

Since no public exploit exists, we simulate exploitation:

1. Reconnaissance: Identify WordPress sites using the plugin via Shodan dorks or WPScan.
2. Endpoint Discovery: Use a wordlist to find AJAX actions (e.g., admin-ajax.php?action=internal_link_update).
3. Exploit Payload: Send a crafted POST request without authentication:

   curl -X POST http://target/wp-admin/admin-ajax.php \
     -d 'action=internal_link_update&post_id=1&link_data=malicious'
   

4. Verification: Check if the link data was modified without authentication.

Blue Team (Detection & Defense)

• Monitor AJAX Requests: Log all admin-ajax.php requests, especially those with unknown or suspicious actions.
• Capability Auditing: Ensure all AJAX handlers check current_user_can().
• Web Application Firewall (WAF): Block requests to admin-ajax.php with missing nonce or suspicious parameters.
• Plugin Hardening: Disable the plugin until a patch is available.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP POST requests to /wp-admin/admin-ajax.php with action parameter containing internal_link or similar.
  • Unusual link_data values in POST body (e.g., base64-encoded strings).
• File IOCs:
  • Modified wp_postmeta table entries with _internal_link meta key.
  • Plugin files with unexpected modifications (check file integrity).
• Log IOCs:
  • Repeated 403 errors from admin-ajax.php (if WAF blocks).
  • Access logs showing unauthenticated POST to AJAX endpoints.

Detection Engineering

YARA Rule

rule CVE_2025_49884_WordPress_Plugin {
    meta:
        description = "Detects missing authorization in Internal Linking of Related Contents plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-49884"
    strings:
        $ajax_action = "internal_link" nocase
        $vuln_func = "wp_ajax_nopriv_" nocase
        $no_cap = "current_user_can" nocase
    condition:
        $ajax_action and $vuln_func and not $no_cap
}

Sigma Rule

title: CVE-2025-49884 - Missing Authorization in Internal Linking Plugin
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects unauthenticated AJAX requests to vulnerable plugin endpoints
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'admin-ajax.php'
        cs-uri-query|contains: 'action=internal_link'
    condition: selection
falsepositives:
    - Legitimate admin actions (if nonce is present)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-49884 - Missing Authorization in Internal Linking Plugin";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"admin-ajax.php"; http_uri;
    content:"action=internal_link"; http_client_body;
    classtype:attempted-admin;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

1. Immediate Action: Disable the plugin until a patch is released.
2. Workaround: Implement a custom function to add capability checks to all AJAX endpoints:

   add_action('init', function() {
       if (defined('DOING_AJAX') && DOING_AJAX) {
           // Add capability checks for all plugin actions
       }
   });
   

3. Long-term: Replace the plugin with an alternative that has proper authorization.
4. Monitoring: Continuously monitor for plugin updates from the vendor.
5. WAF Rules: Deploy virtual patching via WAF to block unauthenticated requests to plugin endpoints.

Valters IT
DevSecOps & Cyber Threat Intelligence