CVE-2024-4019

Executive Summary

CVE-2024-4019 is a critical deserialization vulnerability in the Byzoro Smart S80 Management Platform (up to version 20240411). The flaw resides in the /importhtml.php file, where the sql parameter is unsafely deserialized, allowing remote attackers to execute arbitrary code or manipulate application logic. With a CVSS score of 6.3 (Medium), the vulnerability is remotely exploitable without authentication. Public exploit code has been released, increasing the risk of active exploitation. No patch is available as the vendor has not responded to disclosure attempts.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects a proprietary management platform.

CVSS Breakdown & Threat Level

• CVSS Score: 6.3 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: Low (C:L)
• Integrity Impact: Low (I:L)
• Availability Impact: Low (A:L)

Threat Level: High due to public exploit availability and lack of patch.

Deep Dive & Mechanics

The vulnerability is a classic insecure deserialization flaw in PHP. The /importhtml.php endpoint accepts a sql parameter that is passed to PHP's unserialize() function without proper sanitization. Attackers can craft a malicious serialized object that, when deserialized, triggers arbitrary code execution via PHP gadget chains (e.g., using built-in classes like __destruct or __wakeup magic methods).

Root Cause: The application does not validate or sanitize the sql parameter before deserialization. This allows an attacker to inject arbitrary PHP objects.

Attack Vector: Remote, unauthenticated HTTP POST request to /importhtml.php with a crafted sql parameter.

Impact: Full compromise of the application, including data theft, modification, or denial of service.

Vulnerable vs. Patched Code

Vulnerable Code (hypothetical):

<?php
// /importhtml.php
$sql = $_POST['sql'];
$data = unserialize($sql); // Insecure deserialization
// ... process $data
?>

Patched Code (recommended):

<?php
// /importhtml.php
$sql = $_POST['sql'];
// Use JSON instead of serialization
$data = json_decode($sql, true);
if (json_last_error() !== JSON_ERROR_NONE) {
    die('Invalid input');
}
// ... process $data
?>

Explanation: The patch replaces unserialize() with json_decode(), which does not allow object instantiation. Additionally, input validation should be implemented.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Python 3 with requests library
• Target running Byzoro Smart S80 Management Platform

Exploit Script:

import requests
import php_serialize  # pip install php-serialize

# Craft a malicious serialized object (example using PHPGGC)
# For demonstration, we use a simple gadget chain
payload = 'O:8:"stdClass":0:{}'  # Placeholder - use real gadget chain

url = "http://target/importhtml.php"
data = {"sql": payload}

response = requests.post(url, data=data)
print(response.text)

Usage:

1. Identify a PHP gadget chain for the target environment (e.g., using PHPGGC).
2. Replace payload with the generated serialized object.
3. Run the script to trigger deserialization.

Blue Team

Detection:

• Monitor for POST requests to /importhtml.php with unusual sql parameters.
• Look for serialized PHP objects in HTTP requests (e.g., O:, a:, s: patterns).
• Use WAF rules to block unserialize-like patterns.

Honeypot:

• Deploy a fake /importhtml.php endpoint that logs all requests and alerts on suspicious payloads.

Indicators of Compromise (IOCs)

• Network:
  • POST requests to /importhtml.php with sql parameter containing serialized PHP objects.
  • Unusual outbound connections from the server after exploitation.
• File System:
  • Unexpected files in web root (e.g., webshells).
  • Modified PHP files.
• Logs:
  • PHP error logs showing deserialization errors.
  • Web server logs with importhtml.php in the URI.

Detection Engineering

YARA Rule

rule CVE_2024_4019_Deserialization {
    meta:
        description = "Detects malicious serialized PHP objects targeting CVE-2024-4019"
        author = "Valters IT"
        date = "2024-04-12"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-4019"
    strings:
        $serialized = /O:\d+:"[^"]+":\d+:\{/
        $sql_param = "sql="
    condition:
        $serialized and $sql_param
}

Sigma Rule

title: CVE-2024-4019 Deserialization Attempt
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects attempts to exploit insecure deserialization in Byzoro Smart S80
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: '/importhtml.php'
        cs-uri-query|re: 'sql=O:\d+:'
    condition: selection
falsepositives:
    - Legitimate use of serialized data (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-4019 Deserialization Attempt"; flow:to_server; content:"POST"; http_method; content:"/importhtml.php"; http_uri; content:"sql="; http_client_body; pcre:"/O:\d+:\"[^\"]+\":\d+:\{/"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate affected systems from the internet.
2. Apply WAF rules to block serialized PHP objects in sql parameter.
3. Monitor logs for exploitation attempts.

Long-term Fix:

• Replace unserialize() with json_decode() in /importhtml.php.
• Implement input validation and sanitization.
• Contact vendor for official patch (if available).

Workaround:

• Disable the /importhtml.php endpoint if not needed.
• Use a reverse proxy to filter malicious requests.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert