HSS (Home Subscriber Server)

The Home Subscriber Server is the 4G and 5G evolution of the HLR, used by the MME (4G), AMF and AUSF (5G), and IMS networks to authenticate subscribers and supply policy and service profiles. It stores IMSI/SUPI, long-term Ki/K keys, EPS and 5G subscription data, and integrates with Diameter on the S6a, Cx, and Sh interfaces. The HSS holds the cryptographic root of trust for AKA, so its hardening, strict access controls, separation from interconnect, and Diameter firewalling, is critical to overall network security.

Categories: Core NetworkSignalingRoaming and Interconnect

HSS in context

The mobile core is where subscriber sessions, mobility and policy live. In 4G it is the EPC (MME, HSS, S/PGW); in 5G it is the Service-Based Architecture with AMF, SMF, UPF, AUSF, UDM and the NRF. Core exposure is the difference between a single-subscriber leak and a fleet-wide breach.

Signaling protocols carry the control-plane instructions that set up calls, register subscribers, hand over sessions and route SMS. SS7, Diameter, GTP-C and SIP are the four dominant families, and interconnect exposure of any of them is treated by GSMA FS.11 / FS.19 / FS.20 as a top-tier telecom risk.

To place HSS in the wider telecom-security picture, review HLR, SGSN, FS.07, Pentest, Red Team Exercise and I-CSCF.

Related terms

Equipment

Subscriber registers (HLR, HSS, UDM, UDR, AuC, ARPF)

Articles in the P1 mobile network security guide

Related topic hubs

  • Diameter Security 4G/LTE Diameter threats across IPX/roaming and DEA defenses.
  • 5G Security 5G SBA, SEPP, SUCI, 5G-AKA, N32 and service-based interface security.
  • Diameter Firewall GSMA FS.19 screening at the Diameter Edge Agent on S6a/S9/S13.
  • Signaling Firewall Unified SS7/Diameter/GTP/SMS signaling firewall framework.

More from the TelcoSec Glossary

Browse the full TelcoSec Glossary, the Ultimate Guide to Mobile Network Security, or the P1 Arsenal of telecom-security tools.