CVE-2025-48351

Executive Summary

CVE-2025-48351 is a Cross-Site Request Forgery (CSRF) vulnerability in the WordPress plugin Kento Splash Screen (versions <= 1.4). This flaw allows an attacker to trick an authenticated administrator into performing unintended actions, such as modifying plugin settings or injecting malicious scripts. The CSRF vulnerability leads to Stored Cross-Site Scripting (XSS), enabling persistent payload execution on the WordPress admin dashboard or frontend. The plugin is developed by Pluginspoint and is part of the WordPress ecosystem. No official patch is currently available, and no public exploit code has been released.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. Users should verify the integrity of their plugin files and monitor for updates. Since no patch exists, the supply chain risk is elevated, and users must consider disabling or replacing the plugin.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:L
• Base Score: 7.1 (High)
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: Required (admin must click a crafted link)
• Scope: Changed
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: Low

The threat level is High due to the low attack complexity and the potential for stored XSS, which can lead to persistent compromise of the WordPress admin interface.

Deep Dive & Mechanics

The vulnerability resides in the Kento Splash Screen plugin, which allows administrators to configure a splash screen for their WordPress site. The plugin lacks CSRF tokens in its administrative actions, such as saving settings or updating splash screen content. An attacker can craft a malicious HTML page or link that, when clicked by an authenticated admin, performs a state-changing request (e.g., updating the splash screen HTML to include a malicious script). Because the request is made in the context of the admin's session, the plugin processes it as legitimate.

The stored XSS component arises because the plugin does not sanitize or escape the splash screen content before saving it to the database. Once the malicious content is stored, it is rendered on the site, executing the attacker's JavaScript in the context of the victim's browser. This can lead to session hijacking, defacement, or further exploitation.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is the current state of the plugin. The following is a hypothetical example of the vulnerable code pattern:

Vulnerable Code (kento-splash-screen/admin/settings.php):

<?php
if (isset($_POST['save_splash'])) {
    update_option('kento_splash_content', $_POST['splash_content']);
    // No CSRF check
}
?>

Patched Code (hypothetical):

<?php
if (isset($_POST['save_splash']) && wp_verify_nonce($_POST['_wpnonce'], 'kento_splash_save')) {
    $sanitized_content = wp_kses_post($_POST['splash_content']);
    update_option('kento_splash_content', $sanitized_content);
}
?>

The patch would add a nonce check and sanitize the input using wp_kses_post().

Exploitation & Lab Setup

Red Team (Attack Simulation)

1. Prerequisites: An authenticated WordPress admin session (cookie) for the target site.
2. Craft a CSRF Payload: Create an HTML page that auto-submits a form to the vulnerable endpoint.
3. Deliver Payload: Send the HTML page to the admin via email or social engineering.
4. Execute: When the admin opens the page, the form submits, updating the splash screen with malicious JavaScript.

Example CSRF HTML Payload:

<html>
<body>
<form action="http://target.com/wp-admin/admin-post.php?action=kento_splash_save" method="POST">
    <input type="hidden" name="splash_content" value="<script>alert('XSS')</script>">
    <input type="submit" value="Click me">
</form>
<script>document.forms[0].submit();</script>
</body>
</html>

Blue Team (Detection & Defense)

1. Monitor for CSRF Attacks: Look for unexpected POST requests to admin-post.php with action=kento_splash_save from external referrers.
2. Implement CSRF Tokens: Ensure all admin actions use WordPress nonces.
3. Input Validation: Sanitize and escape all user inputs before saving.
4. Web Application Firewall (WAF): Block requests with suspicious payloads in splash_content.

Indicators of Compromise (IOCs)

• File Hashes (MD5): d41d8cd98f00b204e9800998ecf8427e (example, replace with actual)
• Network Indicators: POST requests to /wp-admin/admin-post.php?action=kento_splash_save with unusual referrers.
• Log Entries: WordPress debug logs showing unexpected update_option calls for kento_splash_content.
• Database Entries: The wp_options table containing kento_splash_content with <script> tags.

Detection Engineering

YARA Rule

rule Detect_Kento_Splash_CSRF_XSS {
    meta:
        description = "Detects malicious CSRF payloads targeting Kento Splash Screen plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-48351"
    strings:
        $xss1 = "<script>" ascii wide nocase
        $xss2 = "onload=" ascii wide nocase
        $xss3 = "onerror=" ascii wide nocase
        $csrf_action = "kento_splash_save" ascii wide nocase
    condition:
        any of ($xss*) and $csrf_action
}

Sigma Rule

title: CSRF Attack Against Kento Splash Screen
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects POST requests to Kento Splash Screen admin action without proper referrer
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: POST
        cs-uri-query|contains: "action=kento_splash_save"
    filter:
        cs-referer|contains: "/wp-admin/"
    condition: selection and not filter
falsepositives:
    - Legitimate admin actions from within wp-admin
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-48351 Kento Splash Screen CSRF Attempt"; flow:to_server,established; content:"POST"; http_method; content:"action=kento_splash_save"; http_uri; content:"<script"; http_client_body; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Disable the Kento Splash Screen plugin until a patch is released.
2. Workaround: Implement a custom CSRF token check by adding a nonce field to the plugin's admin forms.
3. Long-term: Replace the plugin with an alternative that is actively maintained and patched.
4. Monitoring: Enable WordPress audit logging to track changes to plugin settings.
5. User Training: Educate administrators about phishing attacks that exploit CSRF.

Valters IT