# API Fuzzing Bug Bounty

Should be used when the user asks to "test API security", "fuzz APIs", "find IDOR...

- Repository: https://github.com/zebbern/claude-code-guide (4691 stars)
- Category: Testing
- License: MIT
- Last updated: 2026-11-01
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add zebbern/claude-code-guide --skill api-fuzzing-bug-bounty -g -a claude-code -y`
Codex: `npx skills add zebbern/claude-code-guide --skill api-fuzzing-bug-bounty -g -a codex -y`
Cursor: `npx skills add zebbern/claude-code-guide --skill api-fuzzing-bug-bounty -g -a cursor -y`
Gemini CLI: `npx skills add zebbern/claude-code-guide --skill api-fuzzing-bug-bounty -g -a gemini-cli -y`

## Description

This skill should be used when the user asks to "test API security", "fuzz APIs", "find IDOR vulnerabilities", "test REST API", "test GraphQL", "API penetration testing", "bug bounty API testing", or needs guidance on API security assessment techniques.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# API Fuzzing for Bug Bounty

## Purpose

Provide comprehensive techniques for testing REST, SOAP, and GraphQL APIs during bug bounty hunting and penetration testing engagements. Covers vulnerability discovery, authentication bypass, IDOR exploitation, and API-specific attack vectors.

## Inputs/Prerequisites

- Burp Suite or similar proxy tool
- API wordlists (SecLists, api_wordlist)
- Understanding of REST/GraphQL/SOAP protocols
- Python for scripting
- Target API endpoints and documentation (if available)

## Outputs/Deliverables

- Identified API vulnerabilities
- IDOR exploitation proofs
- Authentication bypass techniques
- SQL injection points
- Unauthorized data access documentation

---

## API Types Overview

| Type | Protocol | Data Format | Structure |
|------|----------|-------------|-----------|
| SOAP | HTTP | XML | Header + Body |
| REST | HTTP | JSON/XML/URL | Defined endpoints |
| GraphQL | HTTP | Custom Query | Single endpoint |

---

## Core Workflow

### Step 1: API Reconnaissance

Identify API type and enumerate endpoints:

```bash
# Check for Swagger/OpenAPI documentation
/swagger.json
/openapi.json
/api-docs
/v1/api-docs
/swagger-ui.html

# Use Kiterunner for API discovery
kr scan https://target.com -w routes-large.kite

# Extract paths from Swagger
python3 json2paths.py swagger.json
```

### Step 2: Authentication Testing

```bash
# Test different login paths
/api/mobile/login
/api/v3/login
/api/magic_link
/api/admin/login

# Check rate limiting on auth endpoints
# If no rate limit → brute force possible

# Test mobile vs web API separately
# Don't assume same security controls
```

### Step 3: IDOR Testing

Insecure Direct Object Reference is the most common API vulnerability:

```bash
# Basic IDOR
GET /api/users/1234 → GET /api/users/1235

# Even if ID is email-based, try numeric
/?user_id=111 instead of /?user_id=user@mail.com

# Test /me/orders vs /user/654321/orders
```

**IDOR Bypass Techniques:**

The rest: https://github.com/zebbern/claude-code-guide/blob/HEAD/skills/api-fuzzing-bug-bounty/SKILL.md