International Mobile Station Equipment Identities

In Release 15, the specifications introduced clarifications and corrections to the 5GS mobile identity IE, including resolving editor's notes on its maximum length and completing its definition in messages. The release also included a correction on the 5GS mobile identity IE name itself. Furthermore, it addressed the threat of terminal identity manipulation by acknowledging scenarios where users may modify a terminal's IMEI to gain unauthorized access to services.

• Storing of MPS indicator in non-volatile memory of mobile TS 24.501CR0123
• Clarification on UE identities used for registration TS 24.501CR0452
• Resolution of editor's note on maximum length of the 5GS mobile identity IE TS 24.501CR0503
• Completion of mobile identity IE definition in messages TS 24.501CR0574
• UAC - providing access identities for barring checks of AS triggered access attempts TS 24.501CR0577
• Correction on 5GS mobile identity IE name TS 24.501CR0766

In Release 16, a key update for the IMEI function was that it was explicitly defined as not required for User Equipment (UEs) that access the 5G system via non-3GPP access only. Furthermore, the release formally clarified support for both IMEI and IMEISV identity formats within the system specifications.

• Update of validity conditions for access identities 1 and 2 TS 24.501CR0851
• Clarifications on the validity of access identities TS 24.501CR0949
• IMEI not required for non-3GPP only UEs TS 24.501CR1348
• Re-ordering of text on the applicability of access identities TS 24.501CR1353
• Octet alignment for 5G-GUTI in 5GS mobile identity IE TS 24.501CR1583
• IMEI and IMEISV formats support TS 24.501CR1732

+ 2 more changes

In Release 17, specific enhancements were made to the IMEI function to address the threat of terminal identity manipulation, as identified in the security analysis. The release introduced clarifications for the use of UE identities within procedures like the Remote UE report, ensuring robust handling against masquerading attacks. Furthermore, it resolved encoding errors in identity information elements to improve the integrity of terminal identity data across the system.

• Fix of encoding errors in 5GS mobile identity IE TS 24.501CR2597
• Missing pending NSSAI and rejected NSSAI(s) for the failed or revoked NSSAA for no duplicated PLMN identities or SNPN identities TS 24.501CR3013
• Access identities when UE accesses SNPN using PLMN subscription TS 24.501CR4138
• Resolving the ENs related to the UE Identities used in the Remote UE report procedure TS 24.501CR4614

In Release 18, the IMEI function was enhanced to address security threats related to terminal identity manipulation, as identified in the threat analysis. The updates specifically account for the threat where users may modify the IMEI of a terminal to use it with a valid USIM for unauthorized service access. Furthermore, the release introduced considerations for equivalent Standalone Non-Public Network (SNPN) usage in the context of mobile identity selection and access identities.

• Equivalent SNPN usage for mobile identity selection TS 24.501CR4840
• The equivalent SNPNs usage for access identities TS 24.501CR5084

In Release 19, the IMEI function was updated to address the specific threat of terminal identity manipulation, where users may modify the IMEI of a terminal to use it with a valid USIM for unauthorized service access. This builds upon the foundational security principles by explicitly countering active attacks that involve tampering with terminal equipment identities. The release also included general corrections to mobile identity handling within the 5GS architecture.

• Clarification of the mobile reachable tmer to avoid an expired timer in the unavailability period TS 24.501CR6542
• Corrections to the 5GS mobile identity TS 24.501CR7042