CVE-2025-39425

Executive Summary

CVE-2025-39425 is a Cross-Site Request Forgery (CSRF) vulnerability affecting the Style Manager WordPress plugin by Pixelgrade, versions up to and including 2.2.7. This vulnerability allows an attacker to trick an authenticated administrator into performing unintended actions, such as modifying plugin settings or injecting malicious styles, without their consent. The attack requires user interaction (clicking a crafted link) and has a CVSS v3.1 base score of 4.3 (Medium). No public exploit code or patch is currently available, making this a high-priority issue for WordPress site administrators using the affected plugin.

Supply Chain & Package Security

This vulnerability resides in a WordPress plugin distributed via the official WordPress plugin repository. The plugin is not an NPM, PyPI, Go, or Ruby package, but it is part of the WordPress ecosystem. Administrators should verify the plugin's integrity by checking its checksum against the official repository and monitoring for any unauthorized modifications.

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 to initiate the attack.
• User Interaction (UI): Required (R) – Victim must click a crafted link or visit a malicious page.
• Scope (S): Unchanged (U) – The vulnerable component remains the same.
• Confidentiality Impact (C): None (N) – No data disclosure.
• Integrity Impact (I): Low (L) – Limited modification of plugin settings or styles.
• Availability Impact (A): None (N) – No denial of service.

Threat Level: Medium. The attack requires user interaction, but the impact on integrity could allow an attacker to inject malicious CSS/JavaScript, leading to further compromise (e.g., stored XSS).

Deep Dive & Mechanics

The vulnerability lies in the Style Manager plugin's administrative interface, which fails to implement proper CSRF tokens or nonces for state-changing requests. An attacker can craft a malicious HTML page or email containing a forged request (e.g., changing plugin settings, adding malicious styles). When an authenticated administrator visits the attacker-controlled page, their browser automatically sends the forged request to the WordPress admin panel, executing the action without the administrator's knowledge.

Key Technical Details:

• The plugin uses admin-post.php or admin-ajax.php endpoints without verifying a nonce.
• The attack is blind (no direct response to the attacker), but the action is executed.
• The vulnerability is present in all versions <= 2.2.7.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is presumed to be in the plugin's admin handler functions. A typical vulnerable pattern would be:

// Vulnerable: No nonce check
add_action('admin_post_style_manager_save', 'style_manager_save_settings');
function style_manager_save_settings() {
    update_option('style_manager_settings', $_POST['settings']);
    wp_redirect(admin_url('admin.php?page=style-manager'));
}

A patched version would include a nonce verification:

// Patched: Nonce check added
add_action('admin_post_style_manager_save', 'style_manager_save_settings');
function style_manager_save_settings() {
    if (!isset($_POST['_wpnonce']) || !wp_verify_nonce($_POST['_wpnonce'], 'style_manager_save_nonce')) {
        wp_die('Security check failed.');
    }
    update_option('style_manager_settings', $_POST['settings']);
    wp_redirect(admin_url('admin.php?page=style-manager'));
}

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• A WordPress site with Style Manager plugin <= 2.2.7.
• An authenticated administrator session (victim).

Exploit Steps:

1. Identify a state-changing endpoint (e.g., admin-post.php?action=style_manager_save).
2. Craft a malicious HTML page that auto-submits a form to that endpoint.
3. Host the page on an attacker-controlled server or use a phishing email.
4. Send the link to the victim administrator.
5. When the victim visits the page, the CSRF attack executes.

Example Malicious HTML:

<html>
<body>
<form action="http://target-site.com/wp-admin/admin-post.php" method="POST">
    <input type="hidden" name="action" value="style_manager_save">
    <input type="hidden" name="settings[malicious_css]" value="body { background: red; }">
    <input type="submit" value="Click me">
</form>
<script>document.forms[0].submit();</script>
</body>
</html>

Blue Team (Defense & Detection)

Detection:

• Monitor for unexpected POST requests to admin-post.php or admin-ajax.php with action=style_manager_* parameters.
• Look for referrer headers that do not match the site's own domain.
• Use Web Application Firewall (WAF) rules to block requests missing a valid nonce.

Prevention:

• Ensure the plugin is updated to a patched version (once available).
• Implement CSRF tokens manually if the plugin is not updated.
• Use the SameSite cookie attribute (Lax or Strict) to mitigate CSRF.

Indicators of Compromise (IOCs)

• Network:
  • POST requests to /wp-admin/admin-post.php with action=style_manager_* parameters.
  • Referrer header pointing to an external domain.
• Host:
  • Unexpected changes in the wp_options table under style_manager_settings.
  • Modified CSS/JS files in the uploads directory.
• Logs:
  • WordPress debug log entries showing nonce failures (if patched).
  • Apache/Nginx access logs with unusual POST requests to admin endpoints.

Detection Engineering

YARA Rule

rule CVE_2025_39425_CSRF_StyleManager {
    meta:
        description = "Detects CSRF exploitation attempts against Style Manager plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-39425"
    strings:
        $action = "style_manager_save" nocase
        $admin_post = "admin-post.php" nocase
        $settings = "settings[" nocase
    condition:
        all of them
}

Sigma Rule

title: CVE-2025-39425 CSRF Exploitation Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects CSRF attacks against Style Manager plugin
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        c-uri|contains: '/wp-admin/admin-post.php'
        cs-uri-query|contains: 'action=style_manager_save'
    condition: selection
falsepositives:
    - Legitimate admin actions
level: medium

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-39425 CSRF Exploitation Attempt";
    flow:to_server,established;
    http.method; content:"POST";
    http.uri; content:"/wp-admin/admin-post.php";
    http.client_body; content:"action=style_manager_save";
    classtype:attempted-admin;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin if not critical for operations.
2. Implement a Web Application Firewall (WAF) rule to block requests to admin-post.php with action=style_manager_* parameters from external referrers.
3. Educate administrators about phishing attacks and the importance of verifying URLs before clicking.

Long-Term Fix:

• Apply a patch from the vendor (Pixelgrade) once released.
• If no patch is forthcoming, consider replacing the plugin with an alternative that supports CSRF protection.
• For developers: Add nonce verification to all admin actions using wp_nonce_field() and check_admin_referer().

Valters IT
Securing Digital Frontiers