CVE-2025-3527

Executive Summary

CVE-2025-3527 is a security vulnerability in the EventON Pro WordPress plugin, affecting all versions up to and including 4.9.6. The vulnerability resides in the assets/lib/settings/settings.js file and is due to a missing capability check, allowing authenticated attackers with Subscriber-level access or higher to inject arbitrary web scripts (stored XSS). This can lead to unauthorized modification of data and execution of malicious scripts when other users access the injected pages. The vendor has issued a partial patch in version 4.9.6, but the full remediation status remains unknown. Given the low EPSS score (0.0%) and no public exploit code, the immediate threat is moderate, but the potential for privilege escalation and data theft is significant.

Supply Chain & Package Security

This vulnerability is specific to the WordPress ecosystem, targeting the EventON Pro plugin. It is not related to NPM, PyPI, Go, or Ruby packages. The risk is primarily to WordPress sites using this plugin, where compromised subscriber accounts can lead to persistent XSS attacks.

CVSS Breakdown & Threat Level

• CVSS Score: 6.4 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: Low (Subscriber-level)
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: Low

The threat level is medium due to the low privileges required and the potential for stored XSS, which can be used to steal session cookies, redirect users, or perform actions on behalf of administrators.

Deep Dive & Mechanics

The vulnerability is located in the assets/lib/settings/settings.js file of the EventON Pro plugin. This file handles AJAX requests for saving plugin settings. The missing capability check means that any authenticated user, regardless of role (including Subscriber), can send a crafted request to modify settings or inject malicious JavaScript. The injected script is stored in the WordPress database and executed when an administrator or other user views the affected page (e.g., the EventON settings page or event listings).

The attack flow:

1. An attacker with a Subscriber account logs in.
2. The attacker sends a POST request to the vulnerable endpoint with malicious JavaScript payloads.
3. The plugin saves the payload without proper validation or sanitization.
4. When an administrator accesses the settings page, the script executes, potentially allowing the attacker to create new admin accounts, exfiltrate data, or perform other malicious actions.

Vulnerable vs. Patched Code

The vulnerable code in assets/lib/settings/settings.js lacks a capability check before processing AJAX requests. The partial patch in version 4.9.6 adds a check for manage_options capability, but it may not cover all endpoints.

Vulnerable Code (simplified):

// No capability check
jQuery.ajax({
    url: ajaxurl,
    data: {
        action: 'eventon_save_settings',
        settings: userInput
    },
    success: function(response) {
        // Save settings without validation
    }
});

Patched Code (partial):

// Added capability check
if ( ! current_user_can('manage_options') ) {
    return;
}
jQuery.ajax({
    url: ajaxurl,
    data: {
        action: 'eventon_save_settings',
        settings: sanitizeInput(userInput)
    },
    success: function(response) {
        // Save settings with validation
    }
});

The patch adds a capability check and input sanitization, but the vendor has not confirmed full coverage.

Exploitation & Lab Setup

Red Team

To exploit this vulnerability, an attacker needs a valid WordPress account with Subscriber-level access. The following steps outline a proof-of-concept:

1. Login as a subscriber.
2. Craft a malicious payload (e.g., JavaScript that steals cookies).
3. Send a POST request to the vulnerable endpoint:

   POST /wp-admin/admin-ajax.php HTTP/1.1
   Host: target-site.com
   Content-Type: application/x-www-form-urlencoded
   Cookie: wordpress_logged_in_...
   
   action=eventon_save_settings&settings=<script>alert('XSS')</script>
   

4. Trigger execution by having an admin visit the settings page.

Lab Setup:

• Install WordPress with EventON Pro version 4.9.6 or earlier.
• Create a subscriber account.
• Use Burp Suite or cURL to send the malicious request.
• Monitor for script execution in the admin panel.

Blue Team

To detect exploitation attempts:

• Monitor for unusual AJAX requests to admin-ajax.php with action=eventon_save_settings from low-privilege users.
• Look for script tags or suspicious JavaScript in settings data.
• Use Web Application Firewall (WAF) rules to block XSS payloads.

Indicators of Compromise (IOCs)

• Network IOCs:
  • POST requests to /wp-admin/admin-ajax.php with action=eventon_save_settings and settings parameter containing <script> tags.
  • Unusual outbound connections from the WordPress server to attacker-controlled domains.
• File IOCs:
  • Modified wp-content/plugins/eventon/assets/lib/settings/settings.js file (if patched).
  • Presence of malicious JavaScript in the WordPress database (e.g., in wp_options table).
• User IOCs:
  • Subscriber accounts making administrative-level changes.
  • New admin accounts created by unknown users.

Detection Engineering

YARA Rule

rule CVE_2025_3527_EventON_XSS {
    meta:
        description = "Detects malicious JavaScript injection in EventON Pro settings"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-3527"
    strings:
        $xss_payload = /<script[^>]*>.*?<\/script>/si
        $vulnerable_endpoint = "eventon_save_settings"
    condition:
        $vulnerable_endpoint and $xss_payload
}

Sigma Rule

title: CVE-2025-3527 EventON Pro Stored XSS
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects exploitation attempts of CVE-2025-3527 via AJAX requests
author: Valters IT
logsource:
    category: webserver
    product: apache
    service: access_log
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'action=eventon_save_settings'
        cs-uri-query|re: 'settings=.*<script'
    condition: selection
falsepositives:
    - Legitimate plugin updates
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-3527 EventON Pro Stored XSS Attempt"; flow:to_server; content:"POST"; http_method; content:"/wp-admin/admin-ajax.php"; http_uri; content:"action=eventon_save_settings"; http_client_body; pcre:"/<script[^>]*>.*?<\/script>/si"; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Actions:

   • Update EventON Pro to version 4.9.6 or later (if available).
   • If no patch is available, disable the plugin temporarily.
   • Restrict Subscriber accounts from accessing admin AJAX endpoints via .htaccess or WAF rules.

2. Long-term Measures:

   • Implement a Web Application Firewall (WAF) with XSS protection.
   • Enforce least privilege for WordPress user roles.
   • Regularly audit plugin code for missing capability checks.
   • Monitor for suspicious AJAX requests and user behavior.

3. Workarounds:

   • Add a custom capability check in the plugin's settings.js file (if you have developer access).
   • Use a security plugin like Wordfence to block XSS attempts.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert