HTTPS & VPN Sniffing: UTM Device Risks

TL;DR

Yes, HTTPS and VPN connections can be partially sniffed through a UTM device if it’s not configured correctly. While the content is encrypted, metadata (like websites visited, IP addresses, timestamps) can still be seen. Proper configuration – including SSL inspection/decryption and careful logging policies – is crucial to protect your privacy.

Understanding the Risks

A UTM (Unified Threat Management) device acts as a gateway between your network and the internet. It inspects traffic for security threats, but also has visibility into all data passing through it. Here’s what can be seen:

• Without SSL Inspection: The UTM sees the destination domain name (e.g., www.example.com), source and destination IP addresses, port numbers, and timestamps. It doesn’t see the actual content of your HTTPS session.
• With SSL Inspection: The UTM decrypts the HTTPS traffic, allowing it to inspect the content. This means it can see everything – including usernames, passwords, and sensitive data. However, this also introduces security risks (see section on ‘SSL Inspection Concerns’).
• VPN Connections: If the VPN connection terminates at the UTM device, all traffic is visible to the UTM. Even if the VPN uses strong encryption, the UTM sees who’s connecting to the VPN and when.

Steps to Mitigate Sniffing Risks

1. Enable SSL Inspection (with Caution):
   • SSL inspection decrypts HTTPS traffic for threat analysis.
   • Configure it carefully! Only inspect trusted websites and avoid inspecting sensitive sites like banking or healthcare portals unless absolutely necessary.
   • Ensure the UTM has a valid certificate to prevent man-in-the-middle warnings in browsers.
2. Review Logging Policies:
   • Limit what data your UTM logs. Avoid logging full URLs or sensitive content if possible.
   • Focus on logging metadata like IP addresses, timestamps, and domain names (without the specific path).
   • Regularly review log retention policies to minimize the amount of stored data.
3. VPN Configuration:
   • If using a VPN, ensure it terminates outside your UTM device whenever possible. This means traffic is encrypted before reaching the UTM.
   • Consider split tunneling to route only specific traffic through the VPN.
4. DNS Security:
   • Use a secure DNS provider (e.g., Cloudflare, Google Public DNS) that supports encryption (DNS over HTTPS or DNS over TLS). This prevents your UTM from easily seeing the websites you visit through DNS requests.
5. Regularly Update Firmware:
   • Keep your UTM device’s firmware updated to patch security vulnerabilities that could be exploited for sniffing or data breaches.
6. Monitor Traffic Patterns:
   • Use the UTM’s monitoring tools to identify unusual traffic patterns that might indicate a compromised connection or unauthorized access.

SSL Inspection Concerns

While SSL inspection improves security, it introduces risks:

• Privacy: The UTM can see all your decrypted traffic.
• Security: If the UTM is compromised, attackers could intercept your sensitive data.
• Performance: Decrypting and re-encrypting traffic adds overhead, potentially slowing down network performance.

Checking SSL Inspection Status (Example – Fortigate)

The method varies depending on your UTM vendor. Here’s an example for a Fortigate firewall:

config vpn ssl settings

edit 1

set status enable

end

This shows if SSL inspection is enabled. Consult your UTM’s documentation for specific instructions.