SoftBank Corporation, an investment holding company, faced a significant data breach affecting 137,156 mobile subscribers through compromised third-party infrastructure. The incident involved the unauthorized access to customer names, residential addresses, and phone numbers stored within the systems of UF Japan, an external service provider contracted for telecommunications support operations. The breach did not extend to more sensitive financial data elements, but it highlighted critical failures in vendor security management and persistent vulnerabilities in outsourced data processing operations. The incident exposed the complexity of managing security across multi-vendor environments and the challenges of detecting insider threats.
Source: https://cybersecuritynews.com/softbank-databreach/
TPRM report: https://scoringcyber.rankiteo.com/company/softbank-mobile
"id": "sof606061225",
"linkid": "softbank-mobile",
"type": "Breach",
"date": "6/2025",
"severity": "85",
"impact": "4",
"explanation": "Attack with significant impact with customers data leaks"{'affected_entities': [{'customers_affected': '137,156',
'industry': 'Telecommunications',
'location': 'Japan',
'name': 'SoftBank Corporation',
'type': 'Investment Holding Company'}],
'attack_vector': 'Physical access control vulnerabilities',
'data_breach': {'number_of_records_exposed': '137,156',
'personally_identifiable_information': True,
'type_of_data_compromised': ['Customer names',
'Residential addresses',
'Phone numbers']},
'date_detected': 'March 2025',
'description': 'SoftBank Corporation, an investment holding company, '
'disclosed a significant data breach affecting 137,156 mobile '
'subscribers through compromised third-party infrastructure.',
'impact': {'data_compromised': ['Customer names',
'Residential addresses',
'Phone numbers']},
'initial_access_broker': {'entry_point': 'Physical access control '
'vulnerabilities'},
'lessons_learned': 'Strengthened vendor management protocols, including '
'mandatory security certifications, regular vulnerability '
'assessments, and real-time monitoring integration to '
'prevent similar incidents across their outsourced '
'operations ecosystem.',
'post_incident_analysis': {'corrective_actions': ['Enhanced vendor security '
'assessments',
'Mandatory penetration '
'testing',
'Compliance auditing',
'Continuous security '
'monitoring requirements'],
'root_causes': ['Inadequate physical access '
'controls',
'Perimeter security measures',
'Overly permissive access rights']},
'references': [{'source': 'Japan’s Public Broadcaster, NHK'}],
'regulatory_compliance': {'regulations_violated': ['Japan’s Personal '
'Information Protection '
'Act (PIPA)']},
'response': {'law_enforcement_notified': True,
'remediation_measures': ['Terminating contractual relationship '
'with UF Japan',
'Enhanced vendor security assessments',
'Mandatory penetration testing',
'Compliance auditing',
'Continuous security monitoring '
'requirements']},
'threat_actor': 'Former employee of a partner company within the supply chain',
'title': 'SoftBank Data Breach',
'type': 'Data Breach',
'vulnerability_exploited': ['Inadequate physical access controls',
'Perimeter security measures']}