# nimoca-2026 — nimoca: unauthorized access to the public usage-history service

Incident | Catalog: 0.8.0 | Record SHA-256: b2b77459abf6e36d515a3dc3b8bb0969b2c8545b71a1dfad88bff40632789bf1

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nimoca reported leakage of 521 records through unauthorized service access. Unexpected emails were generated automatically by the service.

Organization: ニモカ | Outcome: confirmed-breach

Occurred: 2026-10-04 | Disclosed: 2026-10-06 | Reviewed: 2026-10-10

Categories: unknown | CVEs: unspecified

## Sourced claims

- [confirmed / Reported fact] Unauthorized public-service access was confirmed. The service, not the attacker, sent the emails. (s1; p.1 §2)
- [confirmed / Reported fact] Affected data comprises 521 records with card numbers, birth dates, and email addresses; name and usage-history leakage is unconfirmed. (s1; p.1 §3 / p.2 §4)

## Reported actions

- [confirmed / Reported fact] The usage-history service was stopped; cause and scope remain under investigation. (s1; p.1 冒頭 / p.2 §6)

## Cause and mitigation hypotheses

These are editorial hypotheses. Assumptions and observations are unverified, not established incident causes, reported responses, or inspection passes.

### legitimate-function-abuse — Cause hypothesis

[hypothesis / editorial-analysis] Abuse of the legitimate input and notification function is a candidate mechanism.

**Primary-source starting point:** The service sent unexpected emails to registered recipients in response to defined input. (s1; p.1 §2 概要)

#### Required assumptions

- The attacker reached the normal flow and it accepted input associated with another user.

#### Observations that would support the hypothesis

- Preserved web and application logs link unauthorized activity to normal endpoints and insufficient ownership checks.

#### Observations that would challenge the hypothesis

- Investigation establishes database access through another path, with email as separate subsequent activity.

#### Limitations

- Email proves the function ran, not an authorization flaw; other paths such as SQL injection remain possible.

Rules: SEC-009, SEC-014

### lookup-ownership-controls — Mitigation hypothesis

[hypothesis / editorial-analysis] Checking ownership before lookup and notification, plus retrieval limits, could curb legitimate-function abuse.

**Primary-source starting point:** The disclosure describes unauthorized public-service access and automated emails containing registration data. (s1; p.1 §2 / p.2 §4)

#### Required assumptions

- Server-side ownership checks are available on lookup and notification paths.

#### Observations that would support the hypothesis

- Two synthetic users in an isolated environment cannot trigger each other’s lookup or notification; retrieval limits work.

#### Observations that would challenge the hypothesis

- Unauthenticated or cross-user input returns data, or bulk lookups and notifications remain unrestricted.

#### Limitations

- Server compromise and other paths remain possible despite these controls; the incident’s specific defect is undisclosed.

Rules: SEC-014

## Timeline

- 2026-10-04: Access occurred around midnight–17:40. A customer report around 09:00 prompted investigation; the service stopped at 17:40. (s1)
- 2026-10-06: Impact and response disclosed. (s1)

## Editorial inspection guidance

unknown: Inspect lookup authorization, input-driven recipients, retrieval limits, and logs. (s1)

## AI attribution

[unknown / Unknown] The reviewed disclosures do not establish attacker use of AI.

## Unknowns

- The specific mechanism is undisclosed; SQL injection and authorization defects are unestablished.

Rules: SEC-009, SEC-014

## Sources

- s1: [nimoca利用履歴照会サービスへの不正アクセスによる情報漏えい](https://www.nimoca.jp/storage/files/information/107/20261006.pdf) — ニモカ; organization; published: 2026-10-06; reviewed: 2026-10-10