Many system administrators who manage VoIP servers, like FreePBX, are advised to change the default SIP port 5060 to enhance security. The idea is straightforward: by moving away from the well-known port, you can hide your server from generic scans and automated attacks that constantly target port 5060. This approach seems logical, and in controlled test environments, it might even appear effective initially. You might set up a test server, change the port, and notice a significant drop in attack attempts on that specific service. You might even successfully connect your VoIP phones to this new port and register trunks with your provider, as described in the original scenario. Outgoing calls might function perfectly, reinforcing the perception of increased security.
However, the problems often begin when you try to receive incoming calls. Like the user in the original post discovered with Vitelity, many VoIP providers expect SIP traffic to arrive on port 5060. They might be configured to only send incoming calls to this standard port. When you inform them of your custom high port, you may encounter resistance or even outright rejection, with support teams indicating their systems are designed to work exclusively with port 5060 for SIP. This immediately raises a crucial question: if VoIP providers don’t fully support non-standard ports, is changing the default SIP port even a viable security strategy in a real-world VoIP environment?
Furthermore, even if you manage to get incoming calls working with a non-standard port through specific configurations or more flexible providers, it’s essential to understand the limitations of port changing as a sole security measure. While it might deter opportunistic scans and script kiddies, it offers minimal protection against determined attackers. Port scanning is a fundamental technique, and sophisticated attackers will quickly identify open ports on your server, regardless of whether they are default or custom. Security through obscurity is generally not considered a robust security practice.
So, what are the alternatives and best practices for securing your VoIP server if simply changing the port isn’t a complete solution? A more effective approach involves a layered security strategy:
-
Firewall and IP Whitelisting: Instead of relying on port obscurity, implement strict firewall rules. Configure your firewall to only allow SIP traffic from the IP addresses of your VoIP provider and your known office locations. This way, even if attackers find your open SIP port, they will be blocked at the firewall level if their IP is not whitelisted. You can restrict access to port 5060 (or your chosen port) to only these necessary IPs.
-
VPN for Remote Phones: For phones located in various offices, consider setting up a Virtual Private Network (VPN). Phones can connect to the VPN, and then all SIP traffic between the phones and the server is encrypted and secured within the VPN tunnel. This eliminates the need to expose your SIP port directly to the public internet for each phone. While the user in the original post wanted to avoid VPN configuration on each phone, it significantly enhances security for distributed phone systems.
-
SIP TLS and SRTP: Implement SIP TLS (Transport Layer Security) and SRTP (Secure Real-time Transport Protocol). TLS encrypts the SIP signaling, protecting registration credentials and call setup information. SRTP encrypts the voice media itself, securing the audio stream. These protocols provide robust encryption and authentication for your VoIP communications, regardless of the port used.
-
Intrusion Detection and Prevention Systems (IDPS): Deploy an IDPS to monitor network traffic for malicious activity. An IDPS can detect and potentially block sophisticated attacks, including SIP-specific attacks, regardless of the port they target.
In conclusion, while changing the default SIP port might offer a superficial sense of security and reduce some automated scans, it’s not a reliable primary security measure for VoIP servers. It often creates compatibility issues with VoIP providers and offers limited protection against determined threats. A comprehensive security strategy should prioritize firewall configurations, IP whitelisting, VPNs for remote access, and robust encryption protocols like SIP TLS and SRTP. Focusing on these methods will provide a much more secure VoIP environment than simply changing the port number, addressing the core issue of securing your server effectively, even if your VoIP provider requires using port 5060.
