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API ​

Theory ​

The API pentesting methodology begins with reconnaissance, where information is gathered about the API, including its endpoints, parameters, and authentication methods. Next, testers assess authentication and authorization to ensure proper access control and attempt to bypass them. Input validation is then tested by sending crafted payloads to identify vulnerabilities like injection attacks. Business logic testing follows, ensuring the API handles data and functions correctly without unintended consequences. Rate limiting and denial-of-service (DoS) protections are evaluated to prevent excessive requests. Finally, a detailed report is created, documenting findings, vulnerabilities, and recommendations for remediation.

Practice ​

API types ​

  • SOAP/XML Web Services : SOAP (Simple Object Access Protocol) is an XML-based protocol for exchanging structured information in the implementation of web services.
  • REST APIs (JSON) : The specificity of a REST API lies in its statelessness, use of standard HTTP methods (GET, POST, PUT, DELETE), and resource-based structure with responses typically formatted in JSON or XML.
  • GraphQL : A query language for APIs offering a complete and understandable description of the data in your API.

Endpoints discovering ​

Discover API endpoint with fuzzing.

FFUF A fast web fuzzer written in Go.

bash
ffuf -w /path/to/wordlist -u https://target/FUZZ

Wordlist for discover API endpoints

chrislockard/api_wordlist

yassineaboukir/List of API endpoints & objects

HTTP method ​

Identify HTTP Method used on the endpoints

HTTPMethods this can be useful to look for HTTP verb tampering vulnerabilities and dangerous HTTP methods.

bash
httpmethods -u http://www.example.com/

Parameter tampering ​

Experiment with adding or replacing parameters in requests to access unauthorized data or functionalities.

Example:

https://target.com/api/users/1 --> 401
https://target.com/api?users=1 --> 200
https://target.com/api/users?1 --> 200

Version testing ​

Older API versions might be more susceptible to attacks. Always check for and test against multiple API versions.

Example:

https://target.com/api/v2/users/1 --> 401
https://target.com/api/v1/users/1 --> 200

Resources ​

hacktricks

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