What is a signaling system 7 (SS7) attack on phone numbers?

[suhashini25]

Can you explain what an SS7 attack is and how it exploits the signaling system to target phone numbers?
What are the common types of SS7 vulnerabilities and attacks on mobile networks?
How do SS7 attacks compromise phone number security?
What are the risks and consequences of an SS7 attack on an individual's phone number?
SS7 attack on phone numbers
SS7 vulnerabilities explained
Mobile network signaling attacks
Phone number security breaches via SS7
SS7 network exploitation
SIM swapping and SS7
Call interception SS7
SMS interception SS7
Location tracking SS7
A Signaling System No. 7 (SS7) attack on phone numbers exploits vulnerabilities in the SS7 protocol, which is the foundational signaling backbone for global telecommunication networks (both landline and mobile, including 2G, 3G, and even some aspects of 4G and 5G operations). Developed decades ago, SS7 was designed with an inherent assumption of trust among interconnected network operators, lacking modern security features like robust authentication and encryption for its signaling messages. This fundamental design flaw makes it susceptible to various malicious exploits once an attacker gains access to the SS7 network.

Here's how SS7 attacks compromise phone number security:

Exploiting Trust and Access:

"Walled Garden" Assumption: SS7 operates on the principle british student data that all entities connected to it (i.e., mobile network operators) are legitimate and trusted. There's minimal validation of message origin or content.
Gaining Access: An attacker doesn't necessarily need to hack a specific mobile operator directly. They can gain access to the SS7 network through various means, such as by purchasing access from a less scrupulous telecom provider (sometimes through legitimate-looking companies that then resell access to bad actors), by hacking a telecom operator's equipment, or even via compromised IoT devices on a network. Once inside, the attacker can send signaling messages that appear legitimate to the network.
Common SS7 Attack Vectors and Their Impact on Phone Numbers:

Location Tracking: Attackers can send specific SS7 queries (like AnyTimeInterrogation or SendRoutingInfoForSM) to a subscriber's Home Location Register (HLR) or Visitor Location Register (VLR). These queries, normally used for call routing or lawful interception, can reveal the real-time location of a mobile device by pinpointing the cell tower it's connected to. The individual whose phone number is being tracked remains completely unaware.

Call and SMS Interception:

SMS Redirection (The Most Common): Attackers can manipulate SS7 messages (e.g., UpdateLocation messages) to trick the network into believing the victim's phone is roaming in a location controlled by the attacker. Consequently, all incoming SMS messages, including crucial One-Time Passwords (OTPs) for two-factor authentication (2FA), bank alerts, and social media verification codes, are redirected to the attacker's device instead of the legitimate user's phone number.
Call Redirection/Eavesdropping: Similarly, an attacker can reroute incoming or outgoing calls through a server they control, enabling them to listen in on conversations. This is often achieved by sending false routing information to the HLR.
Bypassing Two-Factor Authentication (2FA):

This is one of the most critical threats. Many online services rely on SMS-based 2FA as a security layer. By intercepting SMS messages through an SS7 attack, attackers can gain access to banking apps, email accounts, social media profiles, and cryptocurrency wallets, leading to significant financial loss and identity theft.
Denial of Service (DoS):

Attackers can send malicious SS7 messages (e.g., repeated UpdateLocation requests) to overwhelm a subscriber's profile in the HLR or de-register their phone from the network. This can prevent the victim from making or receiving calls and SMS messages, effectively isolating them from communication.
SIM Swapping Facilitation: While SIM swapping often involves social engineering a mobile carrier, SS7 vulnerabilities can sometimes be used to obtain the necessary subscriber information or manipulate network data to facilitate the swap.

Consequences for Individuals:

Financial Fraud: Direct theft from bank accounts, credit card misuse, and cryptocurrency theft.
Identity Theft: Accessing personal accounts and data to impersonate the victim.
Privacy Violation: Eavesdropping on private conversations, reading personal messages, and constant location tracking.
Harassment: Using intercepted information for targeted harassment.
Challenges and Mitigation:

The inherent design of SS7 makes it difficult to secure without fundamental global changes. Many older telecom infrastructures are still reliant on SS7.
Mobile operators are increasingly deploying SS7 firewalls and actively monitoring signaling traffic to detect and filter suspicious messages. However, the sophistication of attacks is also evolving.
For end-users, relying solely on SMS for 2FA is risky. Stronger authentication methods like authenticator apps (e.g., Google Authenticator, Authy) or hardware security keys are recommended as alternatives.
In essence, an SS7 attack leverages the underlying trust model of the global cellular network to compromise the security and privacy of phone numbers, turning them into a conduit for sophisticated cyberattacks.