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A VoIP system connected to the internet is a target. Automated scanners probe SIP ports constantly, looking for weak credentials they can use to place expensive international calls or disrupt service. A short VoIP security checklist, applied consistently, stops most attacks before they succeed.
1. Change Default Credentials
Every default administrator, extension, and SIP password should be changed before the system goes live. Default credentials are the first thing attackers try, and they succeed often enough to remain worthwhile.
2. Enforce Strong SIP Passwords
Use long, random passwords for SIP accounts. Avoid predictable patterns and shared credentials. If the platform supports it, generate passwords automatically rather than letting users choose them.
3. Disable Unused Extensions and Features
Every active extension is an attack surface. Disable accounts for departed employees, unused feature codes, and test extensions. Remove dial-in access that is no longer needed.
4. Restrict Network Access
Management interfaces should never be exposed to the public internet. SIP registration ports should be reachable only from trusted networks, VPN endpoints, or approved carrier addresses. Firewall rules are the first line of defense.
5. Use Encrypted Transport
TLS encrypts SIP signaling so credentials and routing information cannot be intercepted. SRTP encrypts the actual voice media. Enable both wherever endpoints and carriers support them.
6. Set Call Limits
Configure per-extension and per-destination call limits. Block international or premium-rate destinations unless specifically required. Cap concurrent calls and set after-hours restrictions to limit the damage if an account is compromised.
7. Deploy an SBC at the Edge
A Session Border Controller sits between your PBX and the public network, hiding internal topology, filtering malformed traffic, and blocking signaling floods. For organizations with internet-exposed voice traffic, an SBC is standard architecture.
8. Monitor Call Detail Records
Review CDRs regularly for unusual patterns: calls to unexpected countries, high volumes at odd hours, or sudden spikes in call duration. Many toll fraud incidents are visible in call records before they become expensive.
9. Alert on Failed Registrations
A sudden increase in failed registration attempts often signals a brute-force attack. Set alerts so administrators can respond before credentials are guessed.
10. Patch and Update
Keep PBX firmware, gateway firmware, and endpoint software current. Security patches close vulnerabilities that attackers actively exploit. Automated update policies reduce the chance that a system falls behind.
| Layer | Control |
|---|---|
| Endpoints | Strong passwords, encryption, firmware updates |
| PBX | Access control, call limits, patching |
| Network | Firewall rules, VLANs, VPN for remote access |
| Edge | SBC with rate limiting and topology hiding |
| Operations | CDR review, alerting, incident response |
Redstone platforms include the configuration controls needed to implement this checklist, and Redstone SBC products provide hardened edge protection for internet-facing deployments.
Request a VoIP security reviewRedstone Systems, Inc. founded in Delaware, USA in December 2002, has been the ODM vendor for many well-known communications companies, serving the Southeast Asian market. In 2020, Redstone Systems will begin to return to the North America market with its self-developed brand.
Redstone has a complete product line of intelligent voice gateways, providing IP-PBXs, analog VoIP gateways (FXS/FXO), digital VoIP gateways (E1/T1), border appliances, and session boundary controllers (SBCs).
With advanced technology in digital signal processor (DSP), speech coding and speech processing, as well as efficient operational tools such as cloud remote management, auto provisioning, Redstone gateways are widely used in markets of enterprise communications, cloud communications, call centers, operators’ IMS/SIP trunks, bringing users friendly, efficient and reliable communication experience.
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