API Pentesting


Public and private endpoints

Create a list with the public and private endpoints to know which information should be confidential and try to access it in "unathorized" ways.


Search for API patterns inside the api and try to use it to discover more. If you find /api/albums/<album_id>/photos/<photo_id> you could try also things like /api/posts/<post_id>/comment/. Use some fuzzer to discover this new endpoints.

Add parameters

Something like the following example might get you access to another user’s photo album: /api/MyPictureList → /api/MyPictureList?user_id=<other_user_id>

Replace parameters

You can try to fuzz parameters or use parameters you have seen in a different endpoints to try to access other information

For example, if you see something like: /api/albums?album_id=<album id>

You could replace the album_id parameter with something completely different and potentially get other data: /api/albums?account_id=<account id>

Parameter pollution

/api/account?id=<your account id> → /api/account?id=<your account id>&id=<admin's account id>

Wildcard parameter

Try to use the following symbols as wildcards: *, %, _, .

  • /api/users/*

  • /api/users/%

  • /api/users/_

  • /api/users/.

HTTP requet method change

You can try to use the HTTP methods: GET, POST, PUT, DELETE, PATCH, INVENTED to try check if the web server gives you unexpected information with them.

Request content-type

Try to play between the following content-types (bodifying acordinly the request body) to make the web server behave unexpectedly:

  • x-www-form-urlencoded --> user=test

  • application/xml --> <user>test</user>

  • application/json --> {"user": "test"}

Parameters types

If JSON data is working try so send unexpected data types like:

  • {"username": "John"}

  • {"username": true}

  • {"username": null}

  • {"username": 1}

  • {"username": [true]}

  • {"username": ["John", true]}

  • {"username": {"$neq": "lalala"}}

  • any other combination you may imagine

If you can send XML data, check for XXE injections.

If you send regular POST data, try to send arrays and dictionaries:

  • username[]=John

  • username[$neq]=lalala

Play with routes

/files/..%2f..%2f + victim ID + %2f + victim filename

Check possible versions

Old versions may be still be in use and be more vulenrable than latest endpoints

  • /api/v1/login

  • /api/v2/login

  • /api/CharityEventFeb2020/user/pp/<ID>

  • /api/CharityEventFeb2021/user/pp/<ID>

Owasp API Security Top 10

Read this document to learn how to search and exploit Owasp Top 10 API vulnerabilities:

API Security Checklist

List of possible API endpoints

Tools Imperva's customizable API attack tool takes an API specification as an input, generates and runs attacks that are based on it as an output. Another tool for api testing