Critical Vulnerability in VoWiFi Implementations Exposes Millions to Eavesdropping and Fraud
A team of security researchers has discovered critical vulnerabilities in the Voice over Wi-Fi (VoWiFi) implementations of major smartphone manufacturers and mobile network operators (MNOs). This study has highlighted significant security issues in weaknesses in the Diffie-Hellman (DH) key exchange and IPsec tunnels. These vulnerabilities could potentially allow attackers to eavesdrop on private calls, intercept SMS messages, and even impersonate users to commit fraud.
VoWiFi, a technology that allows users to make voice calls over Wi-Fi networks, has become increasingly popular in recent years. However, the research reveals that the implementation of this technology has been riddled with security flaws, leaving users exposed to a range of threats.
One of the key findings of the research is the widespread use of outdated and weak encryption algorithms in VoWiFi implementations. This makes it easier for attackers to intercept and decrypt VoWiFi traffic, potentially gaining access to sensitive information.
A security weakness in the Evolved Packet Data Gateway (ePDG), a crucial network component for LTE and 5G, compromised the communication security of roughly 140 million customers across 13 mobile network providers, including those in Austria, Slovakia, Brazil, and Russia.
The vulnerability stemmed from the improper implementation of IPsec tunnels, a type of VPN used to secure WLAN calls. Instead of using unique, random cryptographic keys, the affected providers relied on a shared set of ten static keys, making it easy for anyone with access to these keys to intercept communications.
“These are ancient methods in themselves and are usually secure. Unless you do something wrong with the keys,” explained Dabrowski, a researcher involved in the discovery. The networks of Chinese provider ZTE were among those affected.
In addition to the ePDG vulnerability, researchers uncovered a further weakness in new MediaTek chips found in several Android smartphone manufacturers like Xiaomi, Oppo, Realme, and Vivo. This vulnerability could potentially allow attackers to compromise user security by weakening the encryption used during VoWiFi registration.
Furthermore, an in-depth analysis of configurations across multiple manufacturers revealed a systemic issue with mobile security. Researchers found outdated cryptographic methods being employed in up to 80% of simulated connections, underscoring the need for industry-wide adoption of enhanced security practices.
The research identified critical vulnerabilities in the initial phase of the key exchange process. Here are the main findings:
- Fallback to Weak Cryptographic Modes: Certain 5G baseband chipsets in some phones allow fallback to weaker, unannounced DH groups. This fallback mechanism was verified experimentally, revealing susceptibility to man-in-the-middle (MitM) attacks.
- Reused Private Keys: Thirteen operators across three continents were found to be using the same globally static set of ten private keys. This reuse compromises the security of the IPsec tunnels, allowing the decryption of any VoWiFi user’s traffic under these operators.
- Deprecated DH Groups: The study discovered that many operators still support deprecated DH groups, which are known to be weak. For example, DH groups with 768-bit and 1024-bit keys are considered insecure by current standards.
- Downgrade Attacks: The research simulated downgrade attacks by intercepting and rewriting VoWiFi traffic. These attacks force the use of weaker DH groups, making the key exchange process more vulnerable to cracking.
The implications of these vulnerabilities are far-reaching. Here are some potential risks:
- Eavesdropping: Attackers could intercept and decrypt VoWiFi calls, gaining access to sensitive conversations and data.
- Impersonation: By injecting maliciously formed SIP messages, attackers could impersonate users or spoof SMS messages.
- Service Disruption: Exploiting these vulnerabilities could lead to service disruptions, affecting the reliability and availability of VoWiFi services.
The researchers have responsibly disclosed these vulnerabilities to the affected manufacturers and MNOs. Patches and updates are being rolled out to address the issues, but users are urged to update their devices and be vigilant about the security of their VoWiFi connections.
