Denny's Legacy App Migration Authentication Forged, Potentially Exposing Customer Data

According to Security NEXT, Denny's Japan discovered on October 30, 2026 that application-related systems had been breached by a third party, potentially exposing personal data of legacy app customers ^[1]. During the system process for migrating from the legacy app to the new version, a third party improperly generated authentication credentials to access certain accounts, potentially exposing email addresses, dates of birth, gender, prefecture of residence, and membership codes ^[1]. The investigation found that system processes for retrieving personal data had been executed, though logs could not distinguish between legitimate customers and third-party actors ^[1].

Industries mainly affected: Hospitality & food service

The investigation found that system processes for retrieving personal data had been executed, though logs could not distinguish between legitimate customers and third-party actors ^[1]