KDDI Email System Breach Exposes 14.2 Million Credentials Across Six Japanese ISPs

Key points

• Email system breach due to third-party software vulnerability
• Up to 14.22 million email addresses and passwords potentially exposed
• Affects KDDI and five other Japanese ISPs (STNet, JCOM, Chubu Telecommunications, Nifty, Biglobe, KDDI Web Communications)

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.

Affected organization

Kddi

Sector: Information

Likely country: Location not provided

Estimated

Threat source

Hacking activity

Watch internet-facing systems, credential abuse and exploit activity.

• Source type: outside the affected organization

Business impact

Potential data exposure

Impact area: Confidentiality

Likely asset: User or customer data

Trend context

72 signals with similar action pattern

• 31 signals in the same sector
• 93 signals with the same likely impact area
• 1 signal linked to this organization/domain

Mentioned entities

KddiData DisclosureMillion Credentials Across Six JapaneseISPs JapaneseKDDIEmailAffects KDDI andJapanese ISPsSTNetJCOM

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 Data Breach Impacts up to 14.2 Million Email Accounts at Six ISPs - Security Affairshttps://securityaffairs.com/174175/data-breach/kddi-data-breach.htmlPublic source from securityaffairs.com.
• 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 Data Breach Impacts up to 14.2 Million Email Accounts at Six ISPs - Security Affairshttps://securityaffairs.co/wordpress/160275/data-breach/kddi-data-breach.htmlPublic source from securityaffairs.co.
• 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.

Jcom·Jun 28, 2026

Same sectorSame action patternSame impact area

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.

Ctc·Jun 28, 2026

Same sectorSame action patternSame impact area

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.

Polymarket·Jun 28, 2026

Same sectorSame action patternSame impact area

Polymarket Suffers $3 Million Crypto Drain via Third-Party Vendor Compromise

Prediction market platform Polymarket disclosed a breach where hackers compromised a third-party vendor. The attackers injected malicious code into the Polymarket website for some users, leading to the draining of approximately $3 million in pUSD (USDC-backed) from at least 11 user wallets. The stolen funds were subsequently swapped and moved to Ethereum. Polymarket has contained the incident, committed to full refunds for affected users, and is in the process of notifying victims. This incident highlights supply-chain vulnerabilities in web frontends and crypto platforms.

Biglobe·Jun 28, 2026

Same sectorSame action patternSame impact area

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.

Kddi Web·Jun 28, 2026

Same sectorSame action patternSame impact area

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.

Stnet·Jun 28, 2026

Same sectorSame action patternSame impact area

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.