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VoIP security best practices for businesses
Voice-over-IP (VoIP) phone systems route calls over the internet, which exposes them to security risks that traditional landlines never faced.
These risks need to be managed across four areas: identities (who can access the system), platforms (cloud services and integrations), endpoints (devices and apps), and networks (firewalls and encryption).
This guide covers the key risks, how businesses secure VoIP in practice, and what to do if something goes wrong.
Contents
- What is VoIP security?
- VoIP security risks, threats and vulnerabilities
- Best practices for VoIP security
- Business VoIP security FAQs
What is VoIP security?
VoIP security is the set of controls and policies designed to protect an organisation’s internet-based phone system from threats such as unauthorised access, fraud, service disruption, and call interception.
It covers four core areas:
- User identities and access: Ensuring only authorised users, devices, and systems can reach the phone system, preventing account takeover and toll fraud.
- Platforms and integrations: Securing the cloud services, PBX software, and third-party tools connected to the phone system through configuration hardening and access controls.
- Network infrastructure: Securing the flow of voice data using firewalls, session border controllers (SBCs), and traffic filtering to block attacks like DDoS or unauthorised traffic injection.
- Endpoints and devices: Protecting IP phones, softphones, and mobile apps through secure configuration, patching, and device-level controls.
VoIP security responsibilities are split between the provider and the organisation. The provider secures the underlying infrastructure while the organisation handles configuration and identity management.
Why VoIP has a broader attack surface than traditional landlines
Business VoIP phone systems have a broader attack surface than traditional landlines because they rely on internet-facing technologies rather than closed, circuit-switched networks.
This brings lower costs and greater flexibility, but also introduces more access points, dependencies, and ways for attackers to interact with the system:
- Exposure to IP networks: Traditional landlines operate on dedicated, carrier-controlled infrastructure with no direct internet access, keeping them largely isolated from external threats. VoIP systems are reachable over IP networks, which significantly increases their exposure.
- Identity-based access: Landline based business phone lines are tied to a physical line and location, so access is inherently limited to the device itself. VoIP systems rely on usernames, passwords, and credentials, which opens the door to identity threats.
- Distributed environments: VoIP spans cloud platforms, PBXs, apps, APIs, and user devices across multiple locations, increasing the number of components and configurations to secure compared to fixed-line telephony.
- Discoverable services: VoIP protocols such as SIP can be scanned and probed when exposed, increasing the risk of unauthorised access if not properly locked down.
- Converged networks: VoIP shares infrastructure with broader IT systems, including data networks, cloud services, and remote access tools. A vulnerability in one area can spill over into voice services, while landlines sit on entirely separate networks.
- AI-driven threats: VoIP systems face modern attack techniques such as AI-powered Vishing, voice spoofing, and automated SIP scanning, none of which apply to traditional landlines.
VoIP security risks, threats and vulnerabilities
VoIP security risk arises when a threat successfully exploits a vulnerability, resulting in measurable business impact.
For example, a toll fraud attack (threat) may exploit weak credentials and a lack of call monitoring (vulnerabilities), resulting in £10,000 in unauthorised call charges (impact). The risk is the likelihood and potential severity of that scenario occurring.
VoIP security risks
The main end-state risks to VoIP systems are:
- Financial loss: Fraudulent call charges, employees tricked into making payments to attackers, or fines due to regulatory breaches such as GDPR.
- Loss of service. System downtime that prevents organisations from making or receiving calls, leading to lost sales and reduced productivity.
- Lateral compromise. Attackers use VoIP as a stepping stone into connected systems such as CRMs, project platforms, or cloud storage.
Other risks, such as data compromise or loss of data integrity, ultimately lead to one of the end-state risks above.
VoIP security threats and vulnerabilities
For VoIP security risks to materialise, attackers must successfully exploit specific weaknesses in systems, identities, and network configurations.
The following are the most common threat patterns, along with the conditions that enable them to succeed.
- Vishing: Attackers impersonate trusted entities using spoofed caller IDs and AI-generated voices, often delivered at scale via SPIT (Spam over Internet Telephony). This succeeds where employees lack cybersecurity awareness training, caller identity is not verified, and inbound call filtering or anti-spam controls are not configured.
- VoIP fraud and account takeover: Unauthorised access to VoIP accounts enables toll fraud and persistent billing abuse, including high volumes of calls to premium-rate or international numbers. This succeeds where SIP endpoints are exposed, authentication is weak, and providers do not enforce call spend limits, anomaly detection, or real-time fraud alerting.
- Credential brute-forcing: Automated login attempts target VoIP admin panels, call recording platforms, and connected integrations to gain unauthorised access. This succeeds where weak or reused passwords are allowed, and MFA is not enforced.
- Insider threats: Employees or contractors misuse VoIP systems due to excessive or outdated access to admin panels, recordings, or billing functions. This succeeds where Joiner-Mover-Leaver processes and conditional access policies are weak, access is not regularly reviewed, and permissions are not tightly controlled.
- DDoS and SIP flooding: Attackers overwhelm VoIP infrastructure with traffic or malformed SIP requests, causing service disruption and outages. This succeeds where systems are publicly exposed and lack protective controls such as firewalls, network load balancers, or session border controllers, particularly in self-hosted deployments.
- VoIP integrations and platform pivoting: Attackers use compromised VoIP accounts or platforms as a foothold to access connected business systems such as CRMs, collaboration tools, UCaaS, or cloud storage. This succeeds where VoIP platforms are tightly integrated with other services, permissions are overly broad, and access between systems is not properly segmented or secured.
Best practices for VoIP security
VoIP security is a shared responsibility between the provider and the organisation. Best practices cover both procuring the right service and ensuring the organisation fulfils its own security obligations.
Best practices for procuring a secure VoIP provider
Encryption, patching, and fraud prevention typically sit with the VoIP provider, making the selection process critical:
- Built-in security features: Ensure the provider supports basic functionality such as end-to-end encryption, fraud detection and automatic patching as standard
- Clear responsibility boundaries: Establish upfront who handles firmware updates, monitoring and incident response
- Compliance certifications: Check for industry-relevant accreditations, such as ISO 27001 and SOC 2.
See our guide to the best business VoIP providers for your consideration.
General best practices for all VoIP systems
Regardless of how the system is deployed, these security practices reduce the most common attack surfaces:
- Strong, unique passwords: Enforce strong credentials on all softphones, web portals and admin dashboards, replacing any defaults.
- Multi-factor authentication: Enable on admin accounts and user logins wherever supported.
- Call monitoring and alerts: Set up automated alerts for suspicious traffic patterns or anomalies, such as unusual international calls or spikes in after-hours activity.
- Disable unused features: Remove IVR, call forwarding rules, international dialling or protocols not actively needed.
- Staff training: Ensure teams can spot social engineering, particularly vishing (voice phishing) attempts targeting phone-based workflows
- Regular security reviews: Revisit settings after adding new users, handsets or locations
Best practices for on-premise VoIP systems
Businesses managing physical hardware or hosting infrastructure on-site take on additional network-level security responsibilities:
- Network segmentation: Run voice traffic on a dedicated VLAN, separate from general data.
- Firewall and ACL restrictions: Open only the ports and IP address ranges required by the provider.
- Firmware updates: Keep handsets, routers, and session border controllers patched and up to date.
Business VoIP security FAQs
Our business VoIP experts answer commonly asked questions about VoIP security:
What cybersecurity regulations do VoIP phone systems need to comply with?
In the UK, businesses using VoIP must comply with the UK GDPR, which governs how personal data captured during calls is stored and processed, including customer login data and call recordings.
If card payments are handled over the phone, PCI DSS compliance is essential to protect cardholder data.
Ofcom also sets standards around call recording, number porting, and network security for telecom providers.
Depending on the sector, additional rules may apply. FCA guidelines cover financial services, while the NHS DSPT applies in healthcare.
What should I do if my VoIP system is hacked?
Act quickly. Disconnect any compromised devices or accounts from the network to limit further damage, and change all passwords and access credentials immediately, including admin logins and user PINs.
Contact the VoIP provider to report the breach. They can help lock down the account and investigate the source. Check call logs for signs of unauthorised usage.
If personal data has been compromised, the business may be legally required to report the breach to the ICO within 72 hours under UK GDPR.
Once the immediate threat is contained, carry out a full security review to close the vulnerability that was exploited.
Is VoIP more secure than traditional phones?
It depends on how it’s set up. Traditional landlines are harder to intercept remotely, but they lack the advanced security features modern VoIP platforms offer, such as end-to-end encryption, multi-factor authentication and real-time threat monitoring.
A properly configured VoIP system with a reputable provider is at least as secure as a landline, and often more so. The risk comes from poor configuration, weak passwords or unpatched software, not from the technology itself.
Is VoIP secure over public Wi-Fi?
Yes, when it’s set up properly. Most modern business VoIP services encrypt calls by default, so they remain secure when intercepted or eavesdropped on, even on public or guest WiFi.
Risk mainly comes from older or misconfigured setups where encryption isn’t enforced.
A VPN adds an extra layer of protection for remote staff, while business SD-WAN solutions secure traffic once users are connected to the company network.
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