The Hidden Risks of SMS: SS7 Vulnerabilities and Roaming Attacks

SMS has been the backbone of mobile communication for decades, but its underlying infrastructure harbors serious security vulnerabilities that most developers and businesses aren't aware of. In this deep dive, we'll explore the technical details of these vulnerabilities and why modern applications need better alternatives.

The SS7 Protocol: A Legacy Security Nightmare

Signaling System 7 (SS7) is the protocol suite that enables SMS, voice calls, and other telecommunications services. Developed in the 1970s, it was designed for a closed network of trusted telecom operators—not the interconnected, threat-rich environment we have today.

How SS7 Attacks Work

SS7 attacks exploit the trust model built into the telecommunications infrastructure:

1. **Network Access**: Attackers gain access to SS7 networks through:

- Compromised telecom operators

- Rogue SS7 gateways

- Purchased access from underground markets

2. **Location Tracking**: Using the `Send Routing Info` command:

```

MAP_SEND_ROUTING_INFO

IMSI: 310150123456789

MSISDN: +15551234567

```

3. **SMS Interception**: Redirecting messages through:

```

MAP_UPDATE_LOCATION

New MSC: attacker_controlled_msc

Target IMSI: 310150123456789

```

Real-World SS7 Attacks

Several high-profile attacks have demonstrated these vulnerabilities:

SIM Swapping: The Social Engineering Vector

SIM swapping attacks bypass technical security by exploiting human vulnerabilities:

The Attack Process

1. **Information Gathering**: Attackers collect personal information through:

- Social media reconnaissance

- Data breaches

- Phishing campaigns

2. **Social Engineering**: Calling the victim's mobile carrier:

```

Attacker: "Hi, I lost my phone and need to transfer my number

to a new SIM card. My name is [victim's name]..."

```

3. **Account Takeover**: Once the number is transferred:

- SMS-based 2FA is compromised

- Password reset codes are intercepted

- Financial accounts are accessed

SIM Swapping Statistics

SMS Roaming Vulnerabilities

International roaming introduces additional attack vectors:

Roaming Attack Scenarios

1. **IMSI Catchers**: Fake cell towers that:

- Intercept SMS messages

- Perform man-in-the-middle attacks

- Downgrade encryption

2. **Malicious Roaming Partners**: Compromised operators can:

- Access subscriber data

- Intercept communications

- Perform location tracking

Technical Details

When roaming, SMS messages traverse multiple networks:

User Device → Visited Network → Home Network → Destination
     ↑              ↑              ↑           ↑
  Vulnerable    Vulnerable    Vulnerable   Vulnerable

Each hop introduces potential interception points.

The Business Impact

Financial Losses

SMS vulnerabilities lead to significant business costs:

Direct fraud: $10.5 billion lost to SMS-based fraud in 2021
Regulatory fines: GDPR fines up to 4% of annual revenue
Reputation damage: Average 7.5% stock price drop after security breaches

Compliance Risks

Regulations increasingly require secure communication:

PCI DSS: Requires secure transmission of cardholder data
HIPAA: Mandates protection of health information
SOX: Requires secure financial communications

Case Study: Banking SMS Vulnerabilities

The Attack

In 2020, a major European bank experienced a sophisticated attack:

1. **Reconnaissance**: Attackers identified high-value targets
2. **SS7 Exploitation**: Used SS7 access to intercept SMS codes
3. **Account Takeover**: Gained access to 847 customer accounts
4. **Financial Theft**: Transferred €2.3 million before detection

The Response

The bank's response included:
Immediate SMS 2FA suspension
Migration to app-based authentication
Customer notification and compensation
Regulatory reporting and fines

Technical Mitigations

Network-Level Protections

Telecom operators can implement:

SS7 Firewall Rules
BLOCK MAP_SEND_ROUTING_INFO FROM untrusted_networks
BLOCK MAP_UPDATE_LOCATION FROM foreign_operators
RATE_LIMIT SMS_DELIVERY_REPORT_REQUEST

Application-Level Solutions

Developers should implement:

1. **Multi-Factor Authentication**:
   ```javascript
   // Don't rely solely on SMS
   const authMethods = [
     'sms_otp',      // Fallback only
     'app_push',     // Primary
     'hardware_key', // Enterprise
     'biometric'     // Mobile
   ];
   ```

2. **Risk-Based Authentication**:
   ```javascript
   function assessRisk(user, context) {
     const riskFactors = {
       newDevice: context.deviceFingerprint.isNew,
       unusualLocation: context.geoLocation.isUnusual,
       roamingNetwork: context.network.isRoaming,
       vpnUsage: context.network.isVPN
     };

     return calculateRiskScore(riskFactors);
   }
   ```

The Inbox Solution

Inbox addresses SMS vulnerabilities through:

End-to-End Encryption

All messages are encrypted using Signal Protocol:

// Message encryption flow
const message = {
  to: '+15551234567',
  type: 'otp',
  body: { code: '123456' }
};

const encryptedMessage = await signalProtocol.encrypt(
  message,
  recipientPublicKey
);

Verified Senders

Only verified businesses can send messages:

1. **Domain Verification**: DNS TXT record validation
2. **Business Verification**: Legal entity confirmation
3. **Code Review**: Application security assessment

Network Isolation

Messages never traverse traditional SMS networks:

App → Inbox API → Encrypted Channel → Inbox App
 ↑                                        ↑
Secure                                 Secure

Migration Strategy

Phase 1: Assessment
Audit current SMS usage
Identify high-risk scenarios
Calculate potential impact

Phase 2: Pilot
Implement Inbox for OTP delivery
Monitor delivery rates and user experience
Gather security metrics

Phase 3: Full Migration
Replace all SMS-based 2FA
Implement rich message types
Decommission SMS infrastructure

Conclusion

SMS vulnerabilities are not theoretical—they're actively exploited by attackers worldwide. The combination of SS7 protocol weaknesses, SIM swapping attacks, and roaming vulnerabilities creates an unacceptable risk for modern applications.

Businesses that continue to rely on SMS for security-critical communications are:
Exposing customers to financial fraud
Violating regulatory requirements
Creating liability for security breaches

The solution is to migrate to modern, secure messaging platforms like Inbox that provide:
End-to-end encryption
Verified sender authentication
Network isolation from legacy vulnerabilities

Resources

[NIST Guidelines on SMS-based Authentication](https://pages.nist.gov/800-63-3/sp800-63b.html#sec5)
[SS7 Security Assessment Tools](https://github.com/P1sec/SigPloit)
[Inbox Security Whitepaper](/security-whitepaper.pdf)
[Migration Planning Template](/migration-template.pdf)