CVE-2021-24146: Modern Events Calendar Lite Disclosure Flaw

CVE-2021-24146 Overview

CVE-2021-24146 is a broken access control vulnerability affecting the Modern Events Calendar Lite WordPress plugin in versions prior to 5.16.5. The vulnerability stems from a lack of authorization checks that did not properly restrict access to export files, allowing unauthenticated users to export all events data in CSV or XML format. This information disclosure flaw enables attackers to harvest sensitive event data without any authentication, potentially exposing personally identifiable information (PII) and confidential business details stored within calendar events.

Critical Impact

Unauthenticated attackers can export all event data from affected WordPress sites, potentially exposing sensitive information including attendee details, event descriptions, and organizational data without requiring any credentials.

Affected Products

• Webnus Modern Events Calendar Lite versions prior to 5.16.5
• WordPress installations running vulnerable Modern Events Calendar Lite plugin
• Sites using Modern Events Calendar Lite for event management and registration

Discovery Timeline

• 2021-03-18 - CVE-2021-24146 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-24146

Vulnerability Analysis

This vulnerability is classified under CWE-284 (Improper Access Control) and CWE-862 (Missing Authorization). The Modern Events Calendar Lite plugin failed to implement proper authorization checks on its export functionality, creating a significant security gap that allows any unauthenticated user to access and download event data.

The core issue lies in the plugin's export endpoints, which process requests for exporting calendar events in various formats including CSV and XML. These endpoints were designed to allow administrators to export event data for backup or migration purposes. However, the plugin developers did not implement authentication or capability checks before processing export requests, meaning any visitor could craft a request to these endpoints and receive a full data export.

Root Cause

The root cause of CVE-2021-24146 is the absence of authentication and authorization verification in the export functionality of the plugin. WordPress plugins typically use capability checks such as current_user_can() to verify that a user has appropriate permissions before allowing sensitive operations. The Modern Events Calendar Lite plugin failed to implement these checks on its export endpoints, treating all incoming export requests as legitimate regardless of the requester's authentication status.

This represents a fundamental secure development oversight where sensitive functionality was exposed without proper access controls, violating the principle of least privilege.

Attack Vector

The attack vector for this vulnerability is network-based and requires no authentication. An attacker can exploit this vulnerability by directly accessing the vulnerable export endpoints on a WordPress site running an affected version of the plugin. The attacker simply needs to send HTTP requests to the export functionality, which will return all stored event data without verifying the requester's identity or permissions.

The exploitation is straightforward and does not require any special tools or complex techniques. An attacker can identify vulnerable sites by detecting the presence of the Modern Events Calendar Lite plugin through standard WordPress fingerprinting methods, then proceed to extract event data by accessing the unprotected export URLs. The exported data may contain sensitive information such as event attendee names, email addresses, phone numbers, event locations, and any custom fields configured for events.

Detection Methods for CVE-2021-24146

Indicators of Compromise

• Unexpected HTTP requests to export-related endpoints in the Modern Events Calendar plugin directory
• Large file downloads containing CSV or XML data from WordPress export endpoints by unauthenticated users
• Access log entries showing repeated requests to plugin export functionality from external IP addresses
• Unusual network traffic patterns indicating bulk data extraction from WordPress installations

Detection Strategies

• Monitor web server access logs for requests to Modern Events Calendar export endpoints without corresponding authenticated sessions
• Implement web application firewall (WAF) rules to detect and alert on unauthenticated access to plugin export functionality
• Review WordPress access logs for patterns consistent with data harvesting or automated export requests
• Deploy file integrity monitoring to detect unauthorized changes to plugin files

Monitoring Recommendations

• Configure alerts for any access to export functionality by unauthenticated users
• Implement rate limiting on export endpoints to slow down potential data extraction attempts
• Monitor for unusual outbound data transfer volumes that may indicate bulk data exfiltration
• Review server logs regularly for signs of exploitation attempts or successful data exports

How to Mitigate CVE-2021-24146

Immediate Actions Required

• Update Modern Events Calendar Lite to version 5.16.5 or later immediately
• Audit WordPress access logs to determine if the vulnerability has already been exploited
• Review exported event data for sensitive information that may require breach notification procedures
• Consider temporarily disabling the plugin if immediate patching is not possible

Patch Information

The vulnerability was addressed in Modern Events Calendar Lite version 5.16.5. Site administrators should update to this version or later to remediate the vulnerability. For detailed information about this vulnerability, refer to the WPScan Vulnerability Database or the Packet Storm Security Advisory.

Workarounds

• Implement web server rules to block unauthenticated access to the plugin's export endpoints
• Use a web application firewall to restrict access to sensitive plugin functionality
• Temporarily disable the Modern Events Calendar Lite plugin until patching can be completed
• Restrict access to WordPress admin directories and plugin files at the server level

# Apache .htaccess configuration to restrict access to plugin export functionality
<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteCond %{REQUEST_URI} modern-events-calendar.*export [NC]
    RewriteCond %{HTTP_COOKIE} !wordpress_logged_in
    RewriteRule .* - [F,L]
</IfModule>