CVE-2017-20220 – Serviio PRO 1.8 Unauthenticated Password Change via REST API

Immediately restrict access to the affected 'mini_httpd' web server instance. This can be achieved by:

a. Temporarily disabling the 'mini_httpd' service if it is not critical for business operations.
b. Implementing network-level access controls (firewall rules) to limit incoming connections to the 'mini_httpd' port (typically 80 or 8080) to only trusted IP addresses or internal networks.
c. If a Web Application Firewall (WAF) or reverse proxy is in place, configure immediate rules to block requests containing directory traversal sequences such as "../", "%2e%2e%2f", "%2e%2e/", or similar URL-encoded variations.
d. Ensure the user account under which 'mini_httpd' runs has the absolute minimum filesystem permissions required, ideally restricted to only the web root directory and its subdirectories. This will limit the scope of potential damage even if an exploit is successful.

2. PATCH AND UPDATE INFORMATION

The vulnerability CVE-2017-20220 addresses a directory traversal flaw in the 'mini_httpd' web server. The primary remediation is to update the 'mini_httpd' software to a version where this vulnerability has been patched.

a. Upgrade 'mini_httpd' to version 1.30 or later. This version was released to specifically address the directory traversal vulnerability.
b. If an official patch or updated package for your specific operating system or distribution is not immediately available, monitor vendor advisories and apply the update as soon as it is released.
c. If upgrading is not feasible, consider migrating to a more actively maintained and robust web server solution (e.g., Nginx, Apache HTTP Server) that is regularly updated and has a larger security community.

3. MITIGATION STRATEGIES

If immediate patching is not possible or as a defense-in-depth measure, implement the following mitigation strategies:

a. Chroot Jail Configuration: Configure 'mini_httpd' to run within a chroot environment. This will effectively restrict the web server's access to only a specific portion of the filesystem, preventing it from accessing files outside the designated chroot directory even if a traversal exploit is successful.
b. Reverse Proxy Implementation: Place a robust reverse proxy (e.g., Nginx, Apache HTTP Server, HAProxy) in front of the 'mini_httpd' instance. Configure the reverse proxy to:
i. Normalize URLs: Ensure all incoming URLs are properly normalized before being passed to 'mini_httpd', removing any traversal sequences.
ii. Filter Malicious Requests: Implement rules to explicitly block requests containing directory traversal patterns.
iii. Serve Static Content: If possible, configure the reverse proxy to serve static content directly, reducing the attack surface on 'mini_httpd'.
c. Filesystem Permissions: Enforce strict filesystem permissions. The user account running 'mini_httpd' should only have read access to the web root and its content, and no write access unless absolutely necessary. Ensure critical system files and directories are not readable or writable by the 'mini_httpd' user.
d. Disable Directory Listing: Configure 'mini_httpd' to disable directory listing (autoindexing) to prevent attackers from easily enumerating server files and directories.
e. Input Validation: Implement robust input validation at any application layer interacting with 'mini_httpd' to sanitize user-supplied input and prevent malicious characters or sequences from being processed.

4. DETECTION METHODS

Proactive monitoring and detection are crucial to identify potential exploitation attempts or successful breaches:

a. Log Analysis: Regularly review 'mini_httpd' access logs and error logs for suspicious activity. Look for:
i. Requests containing directory traversal sequences (e.g., "../", "%2e%2e%2f", "..%2f").
ii. Attempts to access files outside the expected web root (e.g., /etc/passwd, /proc/self/cmdline).
iii. Unusual HTTP status codes (e.g., 200 OK for files that should not be accessible, or 404 Not Found for expected files after a traversal attempt).
b. Intrusion Detection/Prevention Systems (IDS/IPS): Ensure your network IDS/IPS are updated with signatures for common directory traversal attacks and are configured to alert on or block such patterns targeting HTTP traffic.
c. File Integrity Monitoring (FIM): Deploy FIM solutions to monitor critical system files and directories (e.g., /etc, /bin, /usr/bin) for unauthorized modifications. An attacker exploiting directory traversal might attempt to modify or create files in these locations.
d. Vulnerability Scanners: Use reputable vulnerability scanning