Learning from South Korean Telco Breaches

2025 was a bad year for South Korean mobile network operators. All three operators (SK Telecom, KT, LG U+) were affected by breach in some part of their respective network: HSS of SK Telecom, femtocells of KT. Meanwhile, handling of the breach by each operators and post-mortem analysis of each breaches have stark differences. The technical details and implemented mitigations are often buried under the vague terms, and occasionally got lost in translation to English. In this talk, I will cover the technical aspects of SK Telecom and KT's breach, and how the operators are coping to the breach and what kind of measurements have been performed to secure their network. This talk will cover the public information and experiments related to the South Korean telco breaches in 2025. This talk will cover SK Telecom's HSS breach (final results announced), KT's femtocell breach (investigation ongoing) and related operator billing fraud, and revisit Phrack report on KT and LG U+ breach. We also gi