CVE-2023-49859

Executive Summary

CVE-2023-49859 is a Missing Authorization vulnerability in the WordPress plugin Login With Ajax (by Marcus, aka @msykes). The flaw allows an unauthenticated attacker to exploit incorrectly configured access control security levels, potentially leading to unauthorized access to sensitive data or functionality. The vulnerability affects all versions up to and including 4.1. The vendor has not released a patch, and the EPSS score is 0.0%, indicating low exploitation likelihood at this time. However, due to the nature of the flaw and the lack of a fix, it remains a risk for sites using this plugin.

Supply Chain & Package Security

This vulnerability is specific to the WordPress plugin ecosystem. The plugin is distributed via the official WordPress Plugin Directory. Since no patch is available, site administrators must consider removing or replacing the plugin to mitigate risk. The lack of a vendor response increases supply chain risk for any site relying on this plugin.

CVSS Breakdown & Threat Level

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

The vulnerability is classified as Medium severity. While exploitation does not require authentication or user interaction, the impact is limited to low confidentiality loss. The lack of integrity or availability impact reduces the overall threat level, but the missing authorization can still expose sensitive information.

Deep Dive & Mechanics

The Login With Ajax plugin provides AJAX-based login functionality for WordPress. The vulnerability stems from missing authorization checks on certain AJAX actions or REST endpoints. Specifically, the plugin fails to verify that a user has the necessary permissions before executing sensitive operations. This allows an unauthenticated attacker to trigger actions that should be restricted to authenticated users or administrators.

The flaw is categorized under CWE-862: Missing Authorization. The plugin likely registers AJAX handlers without proper capability checks, such as current_user_can() or wp_verify_nonce(). An attacker can craft a request to these endpoints and bypass access controls.

Vulnerable vs. Patched Code

Since no official patch exists, the vulnerable code remains in all versions <= 4.1. The following is a hypothetical example of the vulnerable pattern:

Vulnerable Code (hypothetical):

add_action('wp_ajax_nopriv_my_action', 'handle_my_action');
function handle_my_action() {
    // No capability check
    $data = get_sensitive_data();
    wp_send_json_success($data);
}

Patched Code (hypothetical):

add_action('wp_ajax_nopriv_my_action', 'handle_my_action');
function handle_my_action() {
    if (!current_user_can('manage_options')) {
        wp_die('Unauthorized');
    }
    $data = get_sensitive_data();
    wp_send_json_success($data);
}

The patched version adds a capability check before processing the request.

Exploitation & Lab Setup

Red Team

To exploit this vulnerability, an attacker would:

1. Identify the vulnerable AJAX endpoints by analyzing the plugin's source code or using fuzzing.
2. Craft a simple HTTP request to the endpoint without any authentication tokens.
3. Send the request and observe the response for sensitive data.

Example Exploit (using curl):

curl -X POST http://target.com/wp-admin/admin-ajax.php \
  -d "action=vulnerable_action"

If the endpoint returns data without authentication, the exploit is successful.

Blue Team

To detect exploitation attempts:

1. Monitor for unusual AJAX requests to admin-ajax.php from unauthenticated users.
2. Look for requests with action parameters that are not standard WordPress actions.
3. Implement Web Application Firewall (WAF) rules to block known vulnerable actions.

Detection Rule (WAF):

if ($args ~* "action=(login-with-ajax|vulnerable_action)") {
    return 403;
}

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP requests to /wp-admin/admin-ajax.php with action parameters related to the plugin (e.g., login-with-ajax).
  • Unusual POST requests without Cookie headers.
• File IOCs:
  • Presence of the plugin directory: /wp-content/plugins/login-with-ajax/
  • Modified or unexpected files in the plugin directory.
• Log IOCs:
  • Repeated 200 responses to admin-ajax.php from the same IP without prior authentication.
  • Error logs showing missing capability checks.

Detection Engineering

YARA Rule

rule CVE_2023_49859_Login_With_Ajax {
    meta:
        description = "Detects vulnerable Login With Ajax plugin files"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2023-49859"
    strings:
        $vuln_func = "wp_ajax_nopriv_" ascii wide nocase
        $no_check = "current_user_can" ascii wide nocase
    condition:
        $vuln_func and not $no_check
}

Sigma Rule

title: CVE-2023-49859 - Missing Authorization in Login With Ajax
id: 7b8c9d0e-1f2a-3b4c-5d6e-7f8a9b0c1d2e
status: experimental
description: Detects exploitation attempts against CVE-2023-49859
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        c-uri: '/wp-admin/admin-ajax.php'
        cs-uri-query|contains: 'action=login-with-ajax'
    condition: selection
falsepositives:
    - Legitimate plugin usage
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2023-49859 - Login With Ajax Missing Authorization"; flow:to_server,established; content:"POST"; http_method; content:"/wp-admin/admin-ajax.php"; http_uri; content:"action=login-with-ajax"; http_client_body; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

Since no official patch is available, the following steps are recommended:

1. Immediate Action: Remove or disable the Login With Ajax plugin from all WordPress installations.
2. Alternative: Replace with a maintained alternative plugin that provides similar functionality.
3. Mitigation: If removal is not possible, implement a Web Application Firewall (WAF) rule to block requests to the vulnerable endpoints.
4. Monitoring: Enable detailed logging for AJAX requests and monitor for suspicious activity.
5. Vendor Contact: Attempt to contact the vendor for a patch; if unresponsive, consider forking the plugin and applying a fix.

Valters IT
Securing digital frontiers, one CVE at a time.