SIP Hardening: Secure Your VoIP Calls Against Attacks and Leaks

When you use SIP hardening, the process of securing Session Initiation Protocol (SIP) communications against unauthorized access, eavesdropping, and toll fraud. It's not optional if you're running a business phone system—attackers are already scanning for weak SIP endpoints. Without it, your VoIP system can be hijacked to make thousands of dollars in fake international calls, your calls can be recorded, or your entire phone network can be taken offline by a simple brute-force attack.

SIP hardening isn’t just about adding a password. It’s a layered approach that includes configuring your SIP firewall, a specialized network filter that blocks malicious SIP traffic while allowing legitimate calls, encrypting signaling with SIP over TLS, a protocol that encrypts call setup data to prevent interception, and limiting which IP addresses can reach your PBX. You also need to disable unused features like anonymous SIP calls, change default ports, and enforce strong authentication. Many businesses think their cloud provider handles this for them—but most only secure the cloud side, leaving your local endpoints exposed.

Real-world attacks aren’t theoretical. In 2024, a small law firm lost $18,000 in two days because their SIP trunk had no rate limiting and no firewall. Another company had their auto-attendant hijacked to play ransomware messages to incoming callers. These aren’t rare events. They happen because SIP hardening is often treated like an afterthought. The posts below show you exactly how to fix that—whether you’re using FreePBX, a hosted VoIP service, or a custom Asterisk setup. You’ll find step-by-step guides on configuring SIP trunks securely, detecting brute-force attempts, setting up SRTP encryption without killing call quality, and using tools that actually work in 2025. No fluff. No theory. Just what you need to stop hackers before they call your number.