Telecommunication networks are complex ecosystems, with multiple layers coordinating to deliver connectivity, messaging, and voice services. Among these networks, the SS7 Server protocol plays a vital role in how global operators interact behind the scenes, providing seamless handoffs and roaming for countless subscribers. However, certain vulnerabilities in SS7 infrastructure can be exploited to impersonate users, in ways that echo the results of a SIM swap attack.
Understanding how someone might leverage SS7 signaling to mimic a subscriber identity—much like a classic SIM swap—can reveal potential risks for mobile users. Let’s look deeper into how this is possible, and the wider implications of SS7’s longstanding protocols.
What is SS7 and Why Is It Critical?
SS7, or Signaling System No. 7, connects carriers and networks all over the world, enabling vital services like SMS delivery, call setup, and number portability. When a user sends a text or receives a call, SS7 handles the data exchange in the background. Its development began in the 1970s, and through various updates, it remains the industry standard for switching and routing communications.
Despite the protocol’s significance, its age and global reach have made it a unique target for exploitation. Many SS7 features were designed during a time when trust and closed networks were the norm. As telecommunications became more accessible and interlinked, some aspects of SS7’s trusted architecture left the door open for manipulation.
How Impersonation Works: The SS7 Server and SIM Swap Parallels
At the core of impersonation via SS7 lies a process resembling a SIM swap. In a standard SIM swap fraud, an attacker tricks a mobile provider into issuing a new SIM card for the victim’s number, gaining access to calls, messages, and two-factor authentication codes. With SS7, however, no physical SIM card needs to change hands.
An attacker, using specialized access to an SS7 Server, can send messages to the mobile operator’s network, asking it to reroute the victim’s calls and messages to a device under their control. This can be done from anywhere in the world if the attacker can access SS7 signaling channels, bypassing physical security precautions around SIM cards.
This rerouting works by altering the Home Location Register (HLR) records within a mobile network. The HLR is like an address book that keeps track of subscriber identities and their current network attachments. If a rogue system instructs the network to update its HLR with a different location or routing address, the network will start delivering calls and texts to the attacker instead of the legitimate subscriber.
Implications of Subscriber Impersonation via SS7
The consequences of SS7-based impersonation can be significant for individuals and organizations. Attackers can intercept SMS-based one-time passwords, hijack two-factor authentication processes, and eavesdrop on calls and messages without physically possessing a victim’s device or SIM card. This opens the possibility for a wide array of attacks—ranging from bank account takeovers to extracting sensitive personal information.
Businesses relying on SMS or voice verification may find their security undermined if attackers exploit these weaknesses. Furthermore, nation-states and cybercriminal groups have targeted SS7 vulnerabilities to conduct surveillance or industrial espionage. As more critical operations depend on mobile infrastructure, the incentives for exploiting such network-level flaws only increase.
However, this doesn’t mean the telecommunications industry remains idle. Many operators have begun reinforcing network boundaries with security firewalls, monitoring tools, and anomaly detection systems designed to block unauthorized SS7 signaling. At the same time, experts recommend shifting away from SMS as the primary channel for delivering security codes and verifications, adopting app-based authenticators or biometrics where possible.
Preventing and Detecting SS7 Exploits
Securing against SS7 risks requires a combination of technical improvements and elevated awareness. Mobile operators play the principal role, enforcing strict controls over SS7 access and segmenting trusted partners from potentially hostile networks.
Users are encouraged to be vigilant about notifications of SIM changes or unexpected text messages, as these can indicate tampering, whether through social engineering or network manipulation. Adopting multi-channel authentication where possible, and storing sensitive communications in encrypted channels, further reduces exposure to these threats.
Telecommunications providers are also increasingly collaborating with industry groups and standards bodies to patch legacy vulnerabilities. Firewall solutions, blocking suspicious routing requests and rate-limiting sensitive commands within SS7, provide significant barriers to unauthorized activity. As auditing and reporting mechanisms improve, operators are more likely to spot suspicious rerouting attempts before they impact customers.
Conclusion
Impersonating a subscriber by manipulating SS7 protocols represents a modern variant of the SIM swap technique, but one that operates entirely at the network signaling layer. By rerouting traffic through unauthorized channels, attackers can gain sweeping access without ever obtaining physical hardware from the victim.
The challenge for the industry is to adapt trusted and aging infrastructure to today’s dynamic threat landscape. Continued investment in network monitoring, updated signaling security, and alternative authentication strategies can reduce the risk and keep communication services reliable for everyone.