VoIP Security: Preventing Toll Fraud and SIP Attacks

VoIP systems are frequent targets for toll fraud — attackers gain access to your SIP trunk and make thousands of dollars of international calls billed to your account. This can result in bills of tens of thousands of dollars in a single weekend. Prevention is critical. Security measures: use strong, unique passwords for all extensions and SIP trunk credentials (never use default passwords). Disable international calling for all extensions that don't need it. Set per-extension call spending limits and daily call count limits. Block calling to high-fraud destinations (premium rate numbers, specific country codes) in the outbound dial plan. On the network level: restrict SIP registration to known IP ranges where possible. Use TLS (port 5061) for SIP signaling instead of unencrypted UDP (5060). Enable SRTP for encrypted audio. Configure fail2ban or similar intrusion detection on the PBX to block IPs with repeated failed registration attempts. Review outbound call logs weekly for unusual patterns. Many providers offer real-time fraud alerts — enable these.