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mitsui-fudosan-directory-2026 · Disclosed 2026-09-01

三井不動産: unauthorized access and impact

Business-system credentials were abused; acquisition is under investigation. Maximum potential scope is 19,000 employee and 36,000 external-contact records; these are not confirmed theft counts.

Credentials

Outcome: Confirmed breach

Entry path and evidence

  • Reported fact

    Business-system credentials were abused; acquisition is under investigation.

    [s1]pp.1-2 §§1-3
  • Reported fact

    Maximum potential scope is 19,000 employee and 36,000 external-contact records; these are not confirmed theft counts.

    [s1]pp.1-2 §§1-3

Timeline

  1. Disclosure date established by the reviewed notice. [s1]

Reported response

  • Reported fact

    Credentials were revoked and monitoring and investigation strengthened.

    [s1]pp.1-2 §§1-3

Evidence relevant to prevention

Operational controls to inspect

Inspect the disclosed configuration, authorization or operational issue. Verify applicability and retain evidence of behavior after remediation.

Editorial assessment; not a determination of liability. [s1]

Unknowns and AI involvement

AI involvementUnknown

The reviewed disclosures do not establish attacker use of AI.

The credential-theft route and MFA state are undisclosed. The shopping-membership notice concerns a separate incident.

Sources

  1. [s1] 三井不動産 · Primary source

    三井不動産：事故に関する公表資料 ↗

    Reviewed 2026-10-09