三井住友銀行Data breach / unauthorized access incident
- Occurred on
- October 28, 2026
- Announced on
- November 5, 2026
- Severity
- CLimited data such as email addresses and identifiers.
- Scale
- 227,216 records
- Main impact
- Due to unauthorized access to a subcontractor, 227,216 email addresses of recipients of emails the bank sent between July 1 and October 31 were leaked externally. It is stated that financial information such as account numbers, PINs, and internet banking IDs or passwords are not included.
- Information involved
- Email address
- Cause / key point
- A vulnerability in アララ社's web server and issues in the system environment were exploited, and data was exfiltrated through unauthorized access to the company's service.About Exploitation of vulnerabilities
- Industry
- Finance & insurance
- Last updated
- November 6, 2026
Where to go for this information
The steps themselves are on the protection guide. These links match the kinds of data in this incident, plus support contacts.
Ask AI about this incident
Opens an AI chat with this page's URL already in the prompt. Treat the answer as a starting point — always verify with the official sources listed above.
Is this incident worth paying attention to?
Written & reviewed
Reviewed byYutaro SasaoFounder & CEO, MediaLeap Inc.
CEO of MediaLeap Inc. Working on both sides of web advertising and web media since 2013; founded the company in May 2025.
Review scope: cross-checking against primary sources (official and government announcements), verifying claims stay within the facts, and checking source attribution。Last reviewed:
Written by:Leak Watch editorial team (AI-assisted drafts verified against sources by the editorial team) · Reviewer profile · Request a correction
Related incidents
Browse the database →Incidents sharing the same company, service, attack method or industry (grouped automatically from the disclosures).
Same attack method
- Bユミルリンク（メール配信システムCuenote FC・Cuenote BASE）2026.10.19 announced・Affected 51,628,280 records
- SSHelpfeel（Gyazo）2026.09.16 announced・Affected 23,620,000 records
- SSEストアー(ショップサーブ)2026.10.16 announced・Affected 23,356,000 people
- SSアソビュー2026.11.03 announced・Affected 15,821,184 records
- Cビックカメラ、コジマ、ソフマップ2023.11.02 announced・Affected 14,900,000 records
- SSSKDDI(ISP事業者向けメール基盤)2026.06.23 announced・Affected 12,231,954 people
Same industry
- SSMBCコンシューマーファイナンス2026.11.05 announced・Affected 320,118 people
- Sアフラック生命保険2026.06.30 announced・Affected 4,400,000 people
- SCSアカウンティング株式会社2026.05.15 announced・Affected Unknown
- Sマネーフォワード（GitHub）2026.05.01 announced・Affected 370 records
- A楽天証券2026.10.31 announced・Affected 362 records
- Aライフカード2026.10.28 announced・Affected 339,610 records
Attack method classification: Exploitation of vulnerabilities(Breaking in through holes in software and devices)
Read the Exploitation of vulnerabilities guide and national trends →