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A phone system connected to the internet is discovered by attackers within hours of going live. Automated scanners probe SIP ports around the clock, attempting extension registrations and international call routes they can resell. The financial damage from a successful breach — toll fraud alone costs organizations worldwide billions annually — far exceeds the effort required to prevent it. IP-PBX security hardening is not optional; it is part of the deployment.
Know the Threats
- Toll fraud — attackers register stolen or guessed extension credentials and route international calls through your trunks, often at night or on weekends
- SIP scanning and enumeration — bots probe standard ports to map extensions, versions, and weaknesses
- Credential brute force — weak or default passwords fall to automated attempts within minutes
- Eavesdropping — unencrypted call signaling and audio can be intercepted on the path between sites
- Denial of service — flooding attacks target the voice infrastructure to disrupt business operations
Hardening Practices That Stop Most Attacks
Authentication Discipline
Enforce strong, unique SIP passwords for every extension — auto-generated where possible — and change defaults on day one. Disable or restrict unused extensions and feature codes. Audit registration lists regularly: every unknown endpoint is a finding, not a curiosity.
Network Exposure Control
Restrict SIP and management interfaces to known sources through firewall rules. Remote users connect through VPN or controlled paths rather than exposing registration ports broadly. Management interfaces should never face the public internet.
Call Policy Guardrails
Configure per-extension and per-destination call restrictions: block international dialing where the business does not need it, cap after-hours call authority, and set concurrency limits so a compromised account cannot generate thousands of simultaneous calls. Redstone platforms provide these class-of-service controls at the extension and trunk level.
Encrypted Transport
Use TLS for SIP signaling and SRTP for media where endpoints support it, particularly for traffic crossing untrusted networks. Encryption removes the eavesdropping vector and complicates credential interception.
The Role of an SBC
A Session Border Controller sits between the internet and the PBX, absorbing and filtering the connection layer: hiding topology, rejecting malformed requests, enforcing registration rate limits, and providing topology hiding and DoS protection. For organizations with significant internet-exposed voice traffic, an SBC — combined with the platform hardening above — is the standard architecture. Redstone SBC solutions integrate with REX deployments to provide this boundary.
| Layer | Control | Stops |
|---|---|---|
| Edge | SBC / firewall rules | Scanning, DoS, topology discovery |
| Access | Strong SIP authentication | Registration theft, brute force |
| Policy | Call limits and restrictions | Toll fraud blast calls |
| Transport | TLS / SRTP | Eavesdropping, credential capture |
| Operations | Monitoring and audits | Early detection of anomalies |
Monitor, Audit, Repeat
Security is ongoing: review call detail records for unfamiliar destinations, alert on registration failures spikes, and re-audit configurations after staff changes. Redstone supports administrators with security configuration guidance and hardening checklists so deployments start protected — not after the first fraud incident, but before it.
Request a security hardening 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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