KDDI Corporation Data Breach Exposes 14.2 Million Email Logins Across Six Japanese ISPs
Japanese telecommunications operator KDDI Corporation discovered unauthorized access to its email system on June 17, 2026, which is also used by five other internet service providers. The breach, caused by a vulnerability in third-party software, may have exposed up to 14.2 million email addresses and passwords of current and former customers.
Signal context
First seen: Jun 17, 2026
Last updated: Jun 29, 2026
Status: Public signal
Key points
- Discovery date: June 17, 2026.
- Affected entities: KDDI Corporation, STNet, Inc., JCOM Co., Ltd., Chubu Telecommunications C., Inc., NIFTY Corporation, BIGLOBE Inc., KDDI Web Communications.
- Data exposed: Up to 14.2 million email addresses and passwords.
Signal analysis
BetaThis 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.
Sector: Information
Likely country: Location not provided
Watch internet-facing systems, credential abuse and exploit activity.
- Source type: outside the affected organization
Impact area: Confidentiality
Likely asset: User or customer data
- 27 signals in the same sector
- 90 signals with the same likely impact area
- 1 signal linked to this organization/domain
External sources
Data breach exposes up to 14.2 million email logins at six ISPs - Bleeping Computerhttps://www.bleepingcomputer.com/news/security/data-breach-exposes-up-to-142-million-email-logins-at-six-isps/Public source from bleepingcomputer.com.
KDDI Data Breach Impacts up to 14.2 Million Email Accounts at Six ISPs - Security Affairshttps://securityaffairs.com/194387/data-breach/kddi-data-breach-impacts-up-to-14-2-million-email-accounts-at-six-isps.htmlPublic source from securityaffairs.com.
KDDI Data Breach Impacts up to 14.2 Million Email Accounts at Six ISPs - Security Affairshttps://securityaffairs.co/wordpress/160628/data-breach/kddi-data-breach.htmlPublic source from securityaffairs.co.
KDDI Email System Breach Exposes Up to 14.2 Million Credentials Across Six Japanese ISPs - Rescanahttps://www.rescana.com/post/kddi-email-system-breach-exposes-up-to-14-2-million-credentials-across-six-japanese-ispsPublic source from rescana.com.
KDDI Breach Affects Six Japanese ISPs, Exposes 14.2 Email Credentialshttps://www.infosecurity-magazine.com/news/kddi-breach-japanese-telcos/Public source from infosecurity-magazine.com.
14 M. Sets of Email Info Possibly Leaked in Cyberattack on KDDI | Nippon.comhttps://www.nippon.com/en/news/yjj2026062301023/Public source from nippon.com.
Breach at Japan telecom company may expose up to 14 mln email addresses, passwordshttps://english.news.cn/20260623/92a381492f464ece9e9e605f9be1a5a1/c.htmlPublic source from english.news.cn.
Related signals
Grouped by why the signal is relevant.
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KDDI Web Communications Customer Data Affected by KDDI Email System Breach
KDDI Web Communications, a subsidiary of KDDI, was impacted by the data breach in KDDI Corporation's email system, disclosed on June 28, 2026. The incident, caused by a third-party software vulnerability, led to the potential exposure of up to 14.2 million email addresses and passwords belonging to customers across six Japanese ISPs, including KDDI Web Communications.
Chubu Telecommunications C., Inc. Affected by KDDI Corporation Data Breach
Chubu Telecommunications C., 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. Chubu Telecommunications 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.
JCOM Co., Ltd. Affected by KDDI Corporation Data Breach
JCOM Co., Ltd., 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. JCOM customers' email addresses and passwords may have been compromised.
STNet, Inc. Affected by KDDI Corporation Data Breach
STNet, 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. STNet customers' email addresses and passwords may have been compromised.