KDDI Corporation Data Breach Exposes up to 14.2 Million Email Accounts
Japanese telecommunications operator KDDI Corporation disclosed a data breach where threat actors gained access to one of its email systems, which is also used by five other internet service providers in the country.
Key points
- Threat actors gained unauthorized access to KDDI's email system.
- Intrusion discovered on June 17, 2026.
- Vulnerability in third-party software was exploited.
Connected intelligence
Signal brief
Follow the organization, likely method and potential impact to explore connected Shadow Tier intelligence.
Organization
- Published
- Jun 17, 2026
- Updated
- Jun 30, 2026
- Confidence
- Medium
- Evidence
- 10 sources
Structured assessment
Signal analysis
This analysis groups the signal by industry, likely incident action and impacted security area. It helps compare this signal with other published signals without treating the labels as final determinations.
Threat source
Watch internet-facing systems, credential abuse and exploit activity.
Business impact
- Impact area
- Confidentiality
- Likely asset
- User or customer data
Mentioned entities
Quick context
Questions about this signal
What happened in this signal?
Japanese telecommunications operator KDDI Corporation disclosed a data breach where threat actors gained access to one of its email systems, which is also used by five other internet service providers in the country. The company discovered the intrusion on June 17, 2026, and immediately blocked the attackers. The breach was caused by exploiting a vulnerability in unnamed third-party software used in the email system. Up to 14.2 million email addresses and passwords, including those of current and former customers, may have been exposed.
When was this signal reported?
Shadow Tier lists Jun 17, 2026 as the signal date.
Which organization is connected to this signal?
Kddi is the organization connected to this public signal.
Explore KddiRelated signals
Compare shared topics, actors and incident patterns before opening the full signal.
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South Korean Diplomatic Academy Suffers Significant Data Leak Affecting 10,000 Diplomats
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CTIVD: AIVD en MIVD verwerken persoonsgegevens in bulkdata onrechtmatig
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Related context
NIFTY Corporation Affected by KDDI Corporation Data Breach
NIFTY Corporation, a Japanese internet service provider, was impacted by a data breach originating from an email system provided by KDDI Corporation. Threat actors gained unauthorized access to this shared system by exploiting a vulnerability in third-party software. This led to the potential exposure of up to 14.2 million email addresses and passwords across all affected ISPs. NIFTY Corporation customers' email addresses and passwords may have been compromised.
BIGLOBE Inc. Affected by KDDI Corporation Data Breach
BIGLOBE Inc., a Japanese internet service provider, was impacted by a data breach originating from an email system provided by KDDI Corporation. Threat actors gained unauthorized access to this shared system by exploiting a vulnerability in third-party software. This led to the potential exposure of up to 14.2 million email addresses and passwords across all affected ISPs. BIGLOBE Inc. customers' email addresses and passwords may have been compromised.