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exploiting-excessive-data-exposure-in-api

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Tests APIs for excessive data exposure (OWASP API3:2023) by intercepting raw API responses and comparing them against what the UI actually renders, looking for leaked PII, internal identifiers, debug data, or business-sensitive fields the frontend filters but the API still transmits. Use when auditing REST or mobile-app APIs for over-fetching, response filtering bypass, or unintended data leakage in endpoint responses.

skills/exploiting-excessive-data-exposure-in-api/SKILL.md

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# Exploiting Excessive Data Exposure in API

## When to Use

- Testing APIs where the frontend displays a subset of data but the API response includes additional fields
- Assessing mobile application APIs where responses are designed for multiple client types and may contain excess data
- Identifying PII leakage in API responses that include email addresses, phone numbers, SSNs, or payment data not shown in the UI
- Testing GraphQL APIs where clients can request arbitrary fields including sensitive attributes
- Evaluating APIs after microservice refactoring where internal service-to-service data leaks into public endpoints

**Do not use** without written authorization. Data exposure testing involves capturing and analyzing potentially sensitive personal data.

## Prerequisites

- Written authorization specifying target API endpoints and scope
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