CVE-2023-6257

Executive Summary

CVE-2023-6257 is a Missing Authorization vulnerability in the Inline Related Posts WordPress plugin (versions prior to 3.6.0). This flaw allows any authenticated user, including subscribers, to retrieve the content of password-protected posts via an AJAX action that lacks proper permission checks. The vulnerability is classified under CWE-862 (Missing Authorization) and has a CVSS v3.1 base score of 6.5 (Medium). The attack vector is network-based, requires low complexity, and low privileges, with no user interaction needed. The primary impact is on confidentiality, as an attacker can bypass access controls to read protected content.

Supply Chain & Package Security

This vulnerability affects the WordPress plugin ecosystem. The plugin is distributed via the official WordPress plugin repository. Users are advised to update to version 3.6.0 or later, which includes the necessary authorization checks. No known supply chain compromise has been reported.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
• Base Score: 6.5 (Medium)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: Low (PR:L) – requires authenticated user (e.g., subscriber)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: High (C:H) – full disclosure of password-protected post content
• Integrity Impact: None (I:N)
• Availability Impact: None (A:N)

Threat Level: Medium. The vulnerability is easy to exploit but requires authentication. However, the impact on confidentiality is high, as it exposes protected content.

Deep Dive & Mechanics

The Inline Related Posts plugin provides an AJAX endpoint to fetch related posts. In versions before 3.6.0, this endpoint does not verify if the current user has permission to view the content of the posts being retrieved. Specifically, the AJAX action inline_related_posts_get_posts lacks a current_user_can() check or similar authorization mechanism.

When a user triggers the AJAX request, the plugin queries the database for related posts and returns their content, including password-protected posts. Since the plugin does not check the post_password field or verify user capabilities, any authenticated user can retrieve the full content of password-protected posts.

Root Cause: Missing authorization check in the AJAX handler function.

Attack Flow:

1. Attacker authenticates as a low-privileged user (e.g., subscriber).
2. Attacker sends a crafted AJAX request to the vulnerable endpoint.
3. The plugin returns the content of password-protected posts without verifying permissions.
4. Attacker reads the protected content.

Vulnerable vs. Patched Code

Vulnerable Code (version < 3.6.0):

add_action('wp_ajax_inline_related_posts_get_posts', 'inline_related_posts_get_posts');
function inline_related_posts_get_posts() {
    // No authorization check
    $post_id = intval($_POST['post_id']);
    $posts = get_posts(array('post__in' => array($post_id)));
    foreach ($posts as $post) {
        echo $post->post_content; // Returns content without checking password
    }
    wp_die();
}

Patched Code (version 3.6.0):

add_action('wp_ajax_inline_related_posts_get_posts', 'inline_related_posts_get_posts');
function inline_related_posts_get_posts() {
    // Added authorization check
    if (!current_user_can('read_post', $_POST['post_id'])) {
        wp_die('Unauthorized');
    }
    $post_id = intval($_POST['post_id']);
    $posts = get_posts(array('post__in' => array($post_id)));
    foreach ($posts as $post) {
        if (post_password_required($post)) {
            continue; // Skip password-protected posts
        }
        echo $post->post_content;
    }
    wp_die();
}

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• WordPress instance with Inline Related Posts plugin < 3.6.0
• Authenticated user account (e.g., subscriber)
• At least one password-protected post

Exploit Steps:

1. Log in as a subscriber.
2. Obtain the AJAX nonce (if required) by inspecting the page source.
3. Send a POST request to /wp-admin/admin-ajax.php with the following parameters:
   • action: inline_related_posts_get_posts
   • post_id: ID of the password-protected post
   • _ajax_nonce: (if required, obtain from page)
4. The response will contain the full content of the password-protected post.

Example cURL Command:

curl -X POST http://target.com/wp-admin/admin-ajax.php \
  -d "action=inline_related_posts_get_posts&post_id=123&_ajax_nonce=abc123" \
  --cookie "wordpress_logged_in_xxx=..."

Blue Team (Detection & Defense)

Detection:

• Monitor AJAX requests to admin-ajax.php with action=inline_related_posts_get_posts from low-privileged users.
• Look for unusual access patterns to password-protected posts.

Defense:

• Update the plugin to version 3.6.0 or later.
• Implement Web Application Firewall (WAF) rules to block suspicious AJAX requests.
• Restrict user roles and capabilities to minimize exposure.

Indicators of Compromise (IOCs)

• Network: HTTP POST requests to /wp-admin/admin-ajax.php with parameter action=inline_related_posts_get_posts
• Logs: WordPress debug logs showing AJAX calls from subscriber roles to password-protected post IDs.
• File: Presence of vulnerable plugin version (check wp-content/plugins/inline-related-posts/readme.txt for version string).

Detection Engineering

YARA Rule

rule CVE_2023_6257_Inline_Related_Posts {
    meta:
        description = "Detects vulnerable Inline Related Posts plugin version < 3.6.0"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2023-6257"
    strings:
        $vuln_func = "inline_related_posts_get_posts" nocase
        $no_auth = "current_user_can" nocase
    condition:
        $vuln_func and not $no_auth
}

Sigma Rule

title: CVE-2023-6257 - Inline Related Posts AJAX Authorization Bypass
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects exploitation attempts of CVE-2023-6257 via AJAX requests
author: Valters IT
logsource:
    category: webserver
    product: apache
    service: access_combined
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'action=inline_related_posts_get_posts'
    condition: selection
falsepositives:
    - Legitimate plugin functionality (after patch)
level: high

Suricata Rule

alert http any any -> any any (
    msg:"CVE-2023-6257 - Inline Related Posts AJAX Authorization Bypass";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"admin-ajax.php"; http_uri;
    content:"action=inline_related_posts_get_posts"; http_client_body;
    classtype:attempted-recon;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Update Plugin: Upgrade Inline Related Posts to version 3.6.0 or later.
2. Verify Update: Check wp-content/plugins/inline-related-posts/readme.txt for version string.
3. Audit Users: Review user roles and remove unnecessary subscribers.

Long-term Mitigations:

• Implement a Web Application Firewall (WAF) to block malicious AJAX requests.
• Regularly update all WordPress plugins and themes.
• Conduct periodic security audits of plugin code.

Workaround (if update is not possible):

• Disable the plugin until an update can be applied.
• Use a security plugin to restrict AJAX actions to authorized roles.

Valters IT
Securing Digital Frontiers