Security: Diameter - Interface Deep-Dive

🔗 Critical Signaling Interfaces

1. S6a / S6d (MME/SGSN ↔ HSS)

• Purpose: Authentication, mobility management, and subscriber profile download.
• Key Messages: ULR/ULA (Update Location), AIR/AIA (Authentication Information), IDR/IDA (Insert Subscriber Data).
• Security Objective: Prevent unauthorized profile modification and location tracking.
• Tactical Vulnerability: Location Spoofing. An attacker can send a ULR message from a fake MME to "claim" a subscriber, causing the HSS to update the location and potentially enabling call/SMS interception.

2. Gx (PCEF ↔ PCRF)

• Purpose: Policy control and charging rules.
• Key Messages: CCR/CCA (Credit Control), RAR/RAA (Re-Auth).
• Security Objective: Prevent policy manipulation and service theft.
• Tactical Vulnerability: Policy Hijacking. Unauthorized RAR messages can be used to terminate active sessions or downgrade subscriber QoS.

3. Gy (PCEF ↔ OCS)

• Purpose: Online charging and credit management.
• Key Messages: CCR/CCA (Credit Control - Event/Session/Multi-unit).
• Security Objective: Prevent billing fraud and credit exhaustion.
• Tactical Vulnerability: Credit Exhaustion. Continuous CCR messages with small units can tie up OCS resources or spoof credit usage.

4. S9 (V-PCRF ↔ H-PCRF)

• Purpose: Policy control in roaming scenarios.
• Security Objective: Secure inter-operator policy exchange.
• Tactical Vulnerability: Roaming Data Leakage. Exposure of subscriber policy profiles to visited networks without encryption.

5. Sbc (MME ↔ CBC)

• Purpose: Cell Broadcast Center interface for emergency alerts.
• Security Objective: Authenticate alert sources.
• Tactical Vulnerability: False Alarm Injection. Unauthorized broadcast messages causing public panic.

🧭 Strategic Mapping (itu-t)

!TIPDefensive Strategy: Implement Diameter Edge Agents (DEA) at the network perimeter to perform Topology Hiding and AVP Filtering (Attribute Value Pair) to prevent information leakage about the internal network structure.