HLR (Home Location Register)

The Home Location Register is the master subscriber database in 2G and 3G mobile networks, storing IMSI, MSISDN, service profile, authentication keys, and the current visited network of every subscriber. The MSC, VLR, SMSC, and other network elements query the HLR over MAP/SS7 to authenticate users, route calls and SMS, and apply service permissions. Because compromise of the HLR exposes every subscriber's identity, location, and authentication material, it is one of the most security-sensitive systems in a mobile operator and a primary target for both insider abuse and SS7 attacks.

Categories: Core NetworkSignalingRoaming and Interconnect

HLR 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 HLR in the wider telecom-security picture, review GMLC, STP, HSS, GGSN, MAP and MAP Security.

Related terms

Equipment

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

Articles in the P1 mobile network security guide

Related topic hubs

  • SMS Firewall SMS spam, phishing, A2P bypass and MAP-layer SMS filtering.
  • Signaling Firewall Unified SS7/Diameter/GTP/SMS signaling firewall framework.
  • SS7 Security SS7/MAP/CAP/SCCP attacks and defenses across 2G/3G interconnect.
  • SS7 Firewall GSMA FS.11 category 1/2/3 SS7 message screening at the STP edge.

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.