How to Find API Bugs and Earn Big with Bug Bounties upto $20,000

An API bug is a flaw or vulnerability within an API that can potentially be exploited by attackers. Common API vulnerabilities include:

Authentication flaws (e.g., bypassing login)Authorization issues (e.g., accessing data without permission)Data leaks (e.g., sensitive information exposure)Rate limiting bypass (e.g., sending too many requests without restriction)Broken object-level authorization (BOLA)

These vulnerabilities can lead to unauthorized access to systems, data breaches, or denial-of-service (DoS) attacks.

API bugs are considered one of the most lucrative bugs in the bug bounty ecosystem. The rewards depend on the severity and impact of the bug. Here’s an estimated range of bounty payouts for API bugs:

Low-severity bugs (e.g., small data exposure, minor DoS) typically earn $100 to $1,000.Medium-severity bugs (e.g., bypassing authentication or authorization) can range from $1,000 to $5,000.High-severity bugs (e.g., full account takeover, major data leak) can pay $5,000 to $20,000 or more.Critical-severity bugs (e.g., complete system compromise) can yield $20,000 to $100,000 or even higher on some platforms.

Major bug bounty platforms like HackerOne and Bugcrowd regularly report significant payouts for API bugs. For instance, HackerOne has documented critical API bugs that have earned hackers over $50,000 each.

To maximize your chances of finding API bugs quickly, you’ll need a combination of manual testing and automation tools. Here are some essential tools for API bug hunting:

Burp Suite is a powerful tool for testing web applications and APIs. You can use it to intercept API requests and responses, modify them, and look for potential vulnerabilities like injection flaws, broken authentication, and access control issues.Postman is one of the most popular tools for interacting with APIs. You can use it to send requests, analyze responses, and check if the API is handling requests securely. It’s also helpful for testing edge cases and sending malformed data.OWASP ZAP is an open-source web application security scanner. It can be used to automate security tests, find common vulnerabilities in APIs, and intercept API traffic to look for issues like data leakage and improper access controls.Fiddler is a web debugging proxy that allows you to inspect and modify API requests. It’s useful for analyzing API traffic, looking for flaws in encryption, and testing for vulnerabilities in web and mobile apps.Swagger UI is helpful when reviewing API documentation. API documentation often contains hidden bugs, such as unintended endpoints or incorrect implementation, which can lead to security issues. Cross-checking Swagger documentation against actual API behavior is a smart strategy.For APIs vulnerable to SQL injection, SQLMap is a handy tool. It automates the detection and exploitation of SQL injection flaws, allowing you to test databases behind APIs.If the API uses JSON Web Tokens (JWTs) for authentication or authorization, JWT.io is a useful tool for analyzing and manipulating tokens to check for weaknesses like improper token validation or exposure of sensitive information.

Start by reading the API’s documentation thoroughly to understand its endpoints, authentication mechanisms, and rate limits. API documentation often provides hints or details that help you form an attack plan.Focus on the most common API bugs:Broken authentication: Check if you can bypass authentication using weak tokens, missing headers, or improper token validation.Authorization flaws: Test for broken object-level authorization (BOLA) by accessing data or functions that should be restricted to other users.Rate limiting: Attempt to bypass rate-limiting mechanisms by changing the request source or using different user agents.Input validation: Send malformed requests to see if the API validates input properly.Look for any data leaks, such as sensitive information being included in error messages, response headers, or non-secure endpoints. Always test APIs using both authenticated and unauthenticated access to identify weaknesses.Try to manipulate the intended functionality of the API. For example, can you perform actions not intended for your user role? Does changing a single parameter let you execute admin-level functions?Use Burp Suite, OWASP ZAP, or manual fuzzing to discover hidden or undocumented endpoints. These may not be secured as well as public endpoints.Often, business logic flaws are hidden deep within the API. These include bypassing certain security checks or taking advantage of unanticipated workflows.

Start with common API weaknesses: Authentication and authorization flaws are the most prevalent in API vulnerabilities.Focus on poorly documented APIs: APIs with incomplete or confusing documentation often have hidden vulnerabilities.Automate repetitive tasks: Use tools like Burp Suite’s Intruder feature to automate tasks like fuzzing or sending repeated requests.Test APIs on mobile apps: Many APIs are designed for mobile applications, and flaws often exist in mobile-to-API communication.