CVE-2017-20220

Executive Summary

CVE-2017-20220 is a critical vulnerability in Serviio PRO version 1.8, a media server software. The flaw resides in the Configuration REST API, which lacks proper access control, allowing unauthenticated attackers to modify the mediabrowser login password. This can lead to full compromise of the media server, enabling unauthorized access to media files and potential lateral movement within the network. The vulnerability has a CVSS score of 7.5 (High) and is publicly known, though no official patch has been released. The EPSS score is 0.0%, indicating low exploitation likelihood in the wild, but the risk remains significant for exposed instances.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a standalone software product (Serviio PRO) and does not involve a package manager supply chain.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• Base Score: 7.5 (High)
• Attack Vector: Network (AV:N) – Exploitable remotely.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – Impact confined to the vulnerable component.
• Confidentiality Impact: High (C:H) – Full access to media files and configuration.
• Integrity Impact: High (I:H) – Ability to modify credentials and settings.
• Availability Impact: High (A:H) – Potential denial of service via credential lockout.

Threat Level: High. The vulnerability allows unauthenticated remote attackers to change the mediabrowser password, effectively granting full control over the media server. This can lead to data theft, unauthorized access, and further network compromise.

Deep Dive & Mechanics

The vulnerability exists in the Configuration REST API of Serviio PRO 1.8. The API endpoints responsible for managing user credentials (specifically the mediabrowser login password) do not enforce authentication or authorization checks. An attacker can send specially crafted HTTP requests to these endpoints to modify the password without providing any valid credentials.

Root Cause: The REST API lacks proper access control mechanisms (CWE-306: Missing Authentication for Critical Function). The server does not verify the identity of the requester before allowing changes to sensitive configuration parameters.

Attack Vector: The attacker sends a POST or PUT request to the vulnerable API endpoint (e.g., /rest/configuration/mediabrowser/password) with a new password value. The server processes the request and updates the password, granting the attacker access to the mediabrowser interface.

Impact: Once the password is changed, the attacker can log in to the mediabrowser with the new credentials, gaining access to all media files and potentially other administrative functions. This can lead to data exfiltration, unauthorized streaming, and further exploitation of the network.

Vulnerable vs. Patched Code

Since no official patch is available, the vulnerable code is the entire Serviio PRO 1.8 REST API implementation. The following is a conceptual representation of the vulnerable endpoint:

Vulnerable Code (Conceptual):

# Vulnerable endpoint - no authentication check
@app.route('/rest/configuration/mediabrowser/password', methods=['POST'])
def change_password():
    new_password = request.json.get('password')
    # Directly update password without authentication
    update_mediabrowser_password(new_password)
    return "Password changed", 200

Patched Code (Conceptual):

# Patched endpoint - requires authentication
@app.route('/rest/configuration/mediabrowser/password', methods=['POST'])
@require_auth  # Authentication decorator
def change_password():
    new_password = request.json.get('password')
    # Only update if authenticated
    update_mediabrowser_password(new_password)
    return "Password changed", 200

The patch would involve adding authentication checks (e.g., session tokens, API keys, or basic auth) to all sensitive REST API endpoints.

Exploitation & Lab Setup

Red Team

Exploitation Steps:

1. Identify a Serviio PRO 1.8 instance exposed on the network (e.g., via Shodan or port scanning).
2. Send a POST request to the vulnerable endpoint with a new password:

   curl -X POST http://target:port/rest/configuration/mediabrowser/password \
     -H "Content-Type: application/json" \
     -d '{"password": "newpassword123"}'
   

3. Verify the password change by logging into the mediabrowser interface with the new credentials.
4. Access media files and explore further exploitation opportunities.

Lab Setup:

• Install Serviio PRO 1.8 on a virtual machine (e.g., Ubuntu 16.04).
• Ensure the REST API is accessible over the network.
• Use a separate attacker machine (e.g., Kali Linux) to send the exploit request.

Blue Team

Detection and Response:

• Monitor for unusual POST requests to /rest/configuration/mediabrowser/password without prior authentication.
• Implement network segmentation to isolate Serviio PRO instances from untrusted networks.
• Use a Web Application Firewall (WAF) to block requests to sensitive API endpoints from unauthenticated sources.
• Regularly review logs for unauthorized configuration changes.

Indicators of Compromise (IOCs)

• Network IOCs:
  • POST requests to /rest/configuration/mediabrowser/password from unknown IPs.
  • Unusual login attempts to the mediabrowser interface with new credentials.
• File IOCs:
  • Changes to Serviio configuration files (e.g., serviio.conf) indicating password modification.
• Behavioral IOCs:
  • Unauthorized access to media files or streaming activity from unknown users.

Detection Engineering

YARA Rule

rule CVE_2017_20220_Serviio_Exploit {
    meta:
        description = "Detects exploit attempts for CVE-2017-20220 in network traffic"
        author = "Valters IT"
        date = "2025-04-10"
    strings:
        $s1 = "/rest/configuration/mediabrowser/password" ascii wide nocase
        $s2 = "password" ascii wide nocase
    condition:
        $s1 and $s2
}

Sigma Rule

title: CVE-2017-20220 - Serviio PRO Unauthenticated Password Change
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects POST requests to the Serviio REST API password change endpoint without authentication
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/rest/configuration/mediabrowser/password'
    condition: selection
falsepositives:
    - Legitimate administrative actions (if authentication is implemented)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2017-20220 - Serviio PRO Unauthenticated Password Change"; flow:to_server; content:"POST"; http_method; content:"/rest/configuration/mediabrowser/password"; http_uri; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable Remote Access: If remote access to the Serviio REST API is not required, disable it or restrict access to trusted IPs only.
2. Network Segmentation: Place Serviio PRO instances in a segmented network with strict firewall rules.
3. Manual Authentication: If possible, implement a reverse proxy (e.g., Nginx) with basic authentication in front of the REST API.

Long-Term Fix:

• Upgrade: Check for any updated versions of Serviio PRO that may have addressed this issue. If no patch exists, consider migrating to an alternative media server solution.
• Vendor Contact: Reach out to Serviio support to request a security patch.

Workaround:

• Use a Web Application Firewall (WAF) to block requests to the vulnerable endpoint from untrusted sources.
• Monitor logs for unauthorized access attempts.

Valters IT
Securing Digital Frontiers