Alphabiz - LG Uplus Faces Criticism Over Missed IMSI Security Flaw After 2023 Data Breach

Photo courtesy of Yonhap News

[Alpha Biz= Paul Lee] SEOUL, April 10, 2026 — LG Uplus is facing renewed criticism after announcing a large-scale SIM replacement using randomly generated IMSI numbers, with concerns that the underlying security flaw could have been identified earlier during its 2023 hacking incident.

At the time, personal data of around 300,000 subscribers — including names, phone numbers, and IMSI — was leaked. Critics argue that a detailed analysis of the leaked data could have exposed structural weaknesses in LG Uplus’ IMSI system, which partially incorporates phone numbers.

According to the office of lawmaker Kim Jang-gyeom, investigators focused mainly on breach routes and causes, overlooking potential vulnerabilities in the IMSI structure itself.

Unlike SK Telecom and KT Corporation, which adopted randomized IMSI systems aligned with global standards, LG Uplus retained a legacy structure stemming from earlier network architecture. Experts warn this could increase the risk of subscriber data interception.

The issue was reportedly recognized only in mid-2025, leading to the current SIM replacement plan. Lawmakers criticized both the company and regulators for missing the opportunity to address the problem earlier, calling for stronger oversight and a shift toward identifying structural risks in future cybersecurity investigations.

Alphabiz Reporter Paul Lee(hoondork1977@alphabiz.co.kr)