EFF to FCC: SS7 is Vulnerable, and Telecoms Must Acknowledge That

It’s unlikely you’ve heard of Signaling System 7 (SS7), but every phone network in the world is connected to it, and if you have ever roamed networks internationally or sent an SMS message overseas you have used it. SS7 is a set of telecommunication protocols that cellular network operators use to exchange information and route phone calls, text messages, and other communications between each other on 2G and 3G networks (4G and 5G networks instead use the Diameter signaling system). When a person travels outside their home network's coverage area (roaming), and uses their phone on a 2G or 3G network, SS7 plays a crucial role in registering the phone to the network and routing their communications to the right destination. On May 28, 2024, EFF submitted comments to the Federal Communications Commision demanding investigation of SS7 and Diameter security and transparency into how the telecoms handle the security of these networks.

What Is SS7, and Why Does It Matter?

When you roam onto different 2G or 3G networks, or send an SMS message internationally the SS7 system works behind the scenes to seamlessly route your calls and SMS messages. SS7 identifies the country code, locates the specific cell tower that your phone is using, and facilitates the connection. This intricate process involves multiple networks and enables you to communicate across borders, making international roaming and text messages possible. But even if you don’t roam internationally, send SMS messages, or use legacy 2G/3G networks, you may still be vulnerable to SS7 attacks because most telecommunications providers are still connected to it to support international roaming, even if they have turned off their own 2G and 3G networks. SS7 was not built with any security protocols, such as authentication or encryption, and has been exploited by governments, cyber mercenaries, and criminals to intercept and read SMS messages. As a result, many network operators have placed firewalls in order to protect users. However, there are no mandates or security requirements placed on the operators, so there is no mechanism to ensure that the public is safe.

Many companies treat your ownership of your phone number as a primary security authentication mechanism, or secondary through SMS two-factor authentication. An attacker could use SS7 attacks to intercept text messages and then gain access to your bank account, medical records, and other important accounts. Nefarious actors can also use SS7 attacks to track a target’s precise location anywhere in the world. 

These vulnerabilities make SS7 a public safety issue. EFF strongly believes that it is in the best interest of the public for telecommunications companies to secure their SS7 networks and publicly audit them, while also moving to more secure technologies as soon as possible.

Why SS7 Isn’t Secure

SS7 was standardized in the late 1970s and early 1980s, at a time when communication relied primarily on landline phones. During that era, the telecommunications industry was predominantly controlled by corporate monopolies. Because the large telecoms all trusted each other there was no incentive to focus on the security of the network. SS7 was developed when modern encryption and authentication methods were not in widespread use. 

In the 1990s and 2000s new protocols were introduced by the European Telecommunication Standards Institute (ETSI) and the telecom standards bodies to support mobile phones with services they need, such as roaming, SMS, and data. However, security was still not a concern at the time. As a result, SS7 presents significant cybersecurity vulnerabilities that demand our attention. 

SS7 can be accessed through telecommunications companies and roaming hubs. To access SS7, companies (or nefarious actors) must have a “Global Title,” which is a phone number that uniquely identifies a piece of equipment on the SS7 network. Each phone company that runs its own network has multiple global titles. Some telecommunications companies lease their global titles, which is how malicious actors gain access to the SS7 network. 

Concerns about potential SS7 exploits are primarily discussed within the mobile security industry and are not given much attention in broader discussions about communication security. Currently, there is no way for end users to detect SS7 exploitation. The best way to safeguard against SS7 exploitation is for telecoms to u