CVE-2020-36882

Executive Summary

CVE-2020-36882 is a critical unauthenticated arbitrary file upload vulnerability in Flexsense DiskBoss version 7.7.14. The vulnerability resides in the /Command/Search Files/Directory field, allowing an attacker to upload arbitrary files without authentication. This leads to a denial of service (DoS) by crashing the application. The vulnerability has a CVSS score of 0.0 (likely a placeholder) but based on the vector, it is a high-severity issue with network-based exploitation, low complexity, and no privileges required. No public exploit code or Nuclei template is available, but the vulnerability is confirmed and unpatched.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a standalone application vulnerability in Flexsense DiskBoss.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
• Base Score: 7.5 (High)
• 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: None (C:N)
• Integrity Impact: None (I:N)
• Availability Impact: High (A:H)

The threat level is High due to the ease of exploitation and the potential for denial of service.

Deep Dive & Mechanics

The vulnerability is triggered via the /Command/Search Files/Directory endpoint. The application fails to validate or sanitize user-supplied input in the Directory field, allowing an attacker to upload arbitrary files. This can be exploited by sending a crafted HTTP POST request with a malicious file path or payload. The application then processes this input, leading to a crash due to improper handling of the uploaded file or resource exhaustion.

The root cause is a lack of input validation and authentication checks on the file upload functionality. The application does not verify the file type, size, or origin, and does not require authentication for this endpoint.

Vulnerable vs. Patched Code

Vulnerable Code (DiskBoss 7.7.14): The vulnerable endpoint likely processes the Directory parameter without sanitization. Example pseudo-code:

@app.route('/Command/Search Files/Directory', methods=['POST'])
def search_files():
    directory = request.form['Directory']
    # No validation or authentication
    files = os.listdir(directory)
    return jsonify(files)

Patched Code (Hypothetical): A patched version would include authentication checks and input validation:

@app.route('/Command/Search Files/Directory', methods=['POST'])
def search_files():
    if not authenticated(request):
        return "Unauthorized", 401
    directory = request.form['Directory']
    if not is_valid_path(directory):
        return "Invalid path", 400
    files = os.listdir(directory)
    return jsonify(files)

Exploitation & Lab Setup

Red Team

Exploitation Steps:

1. Identify a target running DiskBoss 7.7.14.
2. Send a crafted HTTP POST request to the /Command/Search Files/Directory endpoint with a malicious payload in the Directory field.
3. The payload can be a path to a large file or a specially crafted string that causes a crash.

Example Exploit (Python):

import requests

target = "http://target.com/Command/Search Files/Directory"
payload = {"Directory": "/dev/random"}  # Example payload to cause resource exhaustion
response = requests.post(target, data=payload)
print(response.status_code)

Blue Team

Detection and Response:

• Monitor for unusual HTTP POST requests to /Command/Search Files/Directory.
• Look for large payloads or unusual directory paths in the Directory field.
• Implement Web Application Firewall (WAF) rules to block requests to this endpoint without authentication.
• Use network monitoring to detect anomalous traffic patterns.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP POST requests to /Command/Search Files/Directory with unusual Directory values.
  • Repeated requests from the same IP address.
• File IOCs:
  • Unexpected files in the application directory.
  • Large temporary files created by the application.
• System IOCs:
  • Application crashes or high resource usage.
  • Error logs indicating file upload failures.

Detection Engineering

YARA Rule

rule CVE_2020_36882_DiskBoss_Upload {
    meta:
        description = "Detects attempts to exploit CVE-2020-36882 in DiskBoss"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2020-36882"
    strings:
        $s1 = "/Command/Search Files/Directory" nocase
        $s2 = "Directory=" nocase
    condition:
        all of them
}

Sigma Rule

title: CVE-2020-36882 DiskBoss Unauthenticated File Upload
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects HTTP POST requests to the vulnerable endpoint
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/Command/Search Files/Directory'
    condition: selection
falsepositives:
    - Legitimate administrative use (if any)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2020-36882 DiskBoss Unauthenticated File Upload"; flow:to_server; content:"POST"; http_method; content:"/Command/Search Files/Directory"; http_uri; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate Actions:
  • Restrict access to the /Command/Search Files/Directory endpoint using firewall rules or WAF.
  • Implement authentication for all file upload endpoints.
  • Monitor logs for exploitation attempts.
• Long-term Fix:
  • Apply patches from Flexsense if available.
  • Upgrade to a patched version of DiskBoss.
  • Conduct a security audit of the application.
• Workarounds:
  • Disable the vulnerable endpoint if not needed.
  • Use a reverse proxy to filter malicious requests.

Valters IT signature: This report is generated by Valters IT for educational and defensive purposes. Unauthorized use of this information for malicious activities is prohibited.