Voice over LTE (VoLTE) marks a significant advancement in telecommunications, enabling voice calls to be transmitted as data packets over LTE networks. Based on Voice over IP (VoIP) technology, VoLTE utilizes the IP Multimedia Subsystem (IMS) for voice traffic, seamlessly integrating voice services with high-speed data capabilities. Initially, mobile operators prioritized improving LTE’s data services, relying on Circuit Switched FallBack (CSFB) to handle voice calls on 2G and 3G networks. However, as 2G and 3G networks are phased out to accommodate 4G and 5G, VoLTE has become the default technology for voice communication, bringing new operational and security challenges.
The rapid deployment of VoLTE, driven by the need to replace legacy networks, has led to security oversights. With over 250 VoLTE networks in operation and many more in development, operators have rushed to implement the technology without fully addressing its vulnerabilities. As VoLTE services grow, particularly in roaming scenarios, networks once considered secure are now exposed to global threats. Accessible management interfaces and open services on VoLTE networks may become prime targets for cyberattacks, underscoring the need for stronger security measures. Despite GSMA’s guidelines, such as GSMA FS.22 (VoLTE Security Analysis and Recommendations) and FS.38 (SIP Network Security), VoLTE remains vulnerable to various threats in its open, all-IP architecture and roaming setups.
As a telecom cybersecurity-focused company, SecurityGen conducts over 100 assessments annually, alongside continuous research, to identify and understand emerging threats and vulnerabilities in telecom networks. Through our extensive VoLTE security assessments and research, we have uncovered management interfaces and unnecessary services that are often accessible to ordinary VoLTE network subscribers. Below are the findings from our detailed research into VoLTE vulnerabilities.
Security Oversights and Their Consequences
The delayed and sometimes hurried implementation of VoLTE has resulted in several critical security oversights. One of the most significant issues is the lack of comprehensive security measures within VoLTE networks, particularly in the IMS core, which serves as the backbone of VoLTE. These shortcomings can expose telecom operators and their subscribers to a range of vulnerabilities.
VoLTE Subscriber Attack Vectors
One of the most alarming vulnerabilities in VoLTE networks is the potential for unauthorized access to the IMS infrastructure. By simply configuring a device to use the IMS Access Point Name (APN) instead of the default internet APN, a malicious actor can gain access to the IMS core. This access opens the door to a variety of attacks, including IP address scanning and service exploitation.
For instance, using tools like Nmap, attackers can scan the IMS subnet for accessible nodes. In many cases, they may find open ports, such as SSH or web management interfaces, that can be exploited to gain control over critical network elements. Even if a full takeover isn’t achieved, attackers can launch Distributed Denial of Service (DDoS) attacks on vulnerable nodes, potentially disrupting network operations.
Moreover, the lack of proper network segmentation in some VoLTE implementations allows for direct IP communication between devices. This flaw can be exploited to set up unauthorized services, such as free internet access for other devices on the same subnet, or to launch targeted attacks against specific subscribers. The risk is further compounded by the fact that many networks do not encrypt signalling and user traffic, leaving sensitive information vulnerable to interception.
SIP Protocol Vulnerabilities in VoLTE
The Session Initiation Protocol (SIP), which is fundamental to VoLTE, has its own set of security challenges. Improper configuration of SIP security controls can lead to information disclosure and other vulnerabilities.
One common issue is the disclosure of internal network identifiers and subscriber information within SIP messages. For example, messages sent to subscribers often contain details such as International Mobile Equipment Identity (IMEI), phone model, and location. Attackers can exploit this information to launch targeted attacks or to gather intelligence for future exploits.
Additionally, the implementation of anonymous calling features in many networks is flawed. While these features are designed to protect the caller’s identity, some networks inadvertently include the caller’s identifier in the SIP messages, allowing attackers to de-anonymize the call. This oversight undermines the privacy protections that these features are supposed to provide.
Furthermore, the lack of protection against SIP flooding attacks in many IMS environments is a significant concern. Without proper rate limiting and other countermeasures, attackers can overwhelm IMS core nodes with SIP requests, causing service disruptions. These attacks can target specific subscribers, rendering them unable to receive calls, or they can be used to launch broader DDoS attacks on the network.
The Path Forward: Strengthening VoLTE Security
To ensure the security of VoLTE networks amidst these security concerns, mobile network operators (MNOs) must implement a series of proactive measures.
Conduct Security Audits:
The first step is to conduct a thorough security audit of VoLTE and VoWiFi connections to the IMS (IP Multimedia Subsystem), identifying potential vulnerabilities and evaluating the overall protection level of the network. This proactive measure allows operators to discover and address hidden vulnerabilities with the necessary protection measures. Moreover, the audit results serve as a foundation for planning more robust, forward-looking security solutions.
Deploy Security Controls:
Implement Access Session Border Controllers (A-SBCs) fronted by IP firewalls to block malicious traffic. This setup, combined with cross-protocol monitoring of SIP, SS7, Diameter, and HTTP/2, enhances security by providing real-time visibility, rapid threat detection, and mitigation.
Ensure Proper Network Segmentation:
Prevent direct connections between subscriber devices and the IMS, minimizing the risk of unauthorized access or attacks.
Activate Existing Features:
Even without dedicated A-SBCs, many security gaps can be addressed by reconfiguring SIP proxies, firewalls, and anti-fraud systems to utilize features already present in deployed hardware. Thus, operators must adopt a proactive approach by implementing robust encryption, secure network architecture, and continuous monitoring to defend against emerging VoLTE threats. The transition to 5G presents a unique opportunity to resolve legacy security issues, ensuring a resilient foundation for the future of telecommunications.
By adhering to GSMA guidelines and embedding regular security audits, encryption, and continuous monitoring into their operations, operators can build a strong, sustainable defense for VoLTE roaming. A security-first approach is essential to achieve a seamless and secure VoLTE rollout.
About SecurityGen
Founded in 2022, SecurityGen is a global company focused on telecom security. We deliver a solid security foundation to drive secure telecom digital transformations and ensure safe and robust network operations. Our extensive product and service portfolio provides complete protection against existing and advanced telecom security threats. www.secgen.com
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