API Testing: A Journey into Reconnaissance and Vulnerability Identification using BurpSuite
Tags: cybersecurity, webdev, vulnerabilities, api
Published: 2024-06-19 03:19:13

Think of API testing as embarking on a thrilling adventure, where you explore uncharted territories to ensure the safety and reliability of your digital assets. This guide will take you through the exciting process of API testing, focusing on reconnaissance and vulnerability identification.

### API Reconnaissance

Before diving into the depths of API testing, you need a solid map like this {% embed https://static.wikia.nocookie.net/callofduty/images/9/94/Isolated_Map_Overview_Season_4_Fool%27s_Gold_CODM.png/revision/latest?cb=20240414070316 %} :) just kidding, not that [COD](https://callofduty.fandom.com/wiki/Call_of_Duty_(series)) Map, but with elements being somewhat similar; points, locations, e.t.c . This involves understanding the lay of the land, or in technical terms, the API's attack surface. Here’s your guide:

1. **Identify API Endpoints**:
   - Endpoints are like landmarks on your journey. They are specific locations where APIs receive requests. For instance, imagine you’re visiting a library (the server) and you want to see a list of books. You’d head to the `/api/books` section.
   - Another landmark could be `/api/books/mystery`, guiding you to a collection of mystery novels. Knowing these endpoints is like having a treasure map—it’s crucial for successful exploration.

2. **Determine Interaction Methods**:
   - To interact with these landmarks, you need the right tools and instructions. Gather details on:
     - **Input Data**: Think of these as the keys to different doors, including both mandatory and optional parameters.
     - **Supported Request Types**: This is akin to knowing if a door requires a push, pull, or a keycard—whether it’s HTTP methods or media formats.
     - **Rate Limits and Authentication Mechanisms**: These are the rules of the land, ensuring you don’t overstay your welcome or enter without permission.

### API Documentation

Imagine having a guidebook that explains everything about your journey. API documentation is that guidebook, and it comes in two forms:

1. **Human-Readable**: Like a travel guide with detailed explanations, examples, and usage scenarios.
2. **Machine-Readable**: Think of it as a GPS system that uses structured formats like JSON or XML for software automation.

**Finding API Documentation**:
- **Browsing Applications**: Use tools like Burp Scanner to explore the API, similar to using a metal detector to find hidden treasures. Look for endpoints such as `/api`, `/swagger/index.html`, or `/openapi.json`.
- **Using Intruder**: Deploy wordlists based on common API conventions, much like using a dictionary to decode an ancient language.

**Using Machine-Readable Documentation**:
- Tools like Burp Scanner can audit OpenAPI documentation, while Postman and SoapUI can help test the documented endpoints, much like testing the integrity of discovered artifacts.

### Identifying and Interacting with Endpoints

**Manual Exploration**:
- Use Burp Repeater and Burp Intruder to interact with identified endpoints. This is like probing different areas of a cave to uncover additional chambers or passageways.

**HTTP Methods**:
- Test various HTTP methods to uncover different functionalities:
  - `GET /api/tasks`: Retrieves tasks, akin to finding a list of quests.
  - `POST /api/tasks`: Creates a new task, like adding a new quest to your log.
  - `DELETE /api/tasks/1`: Deletes a task, removing a quest from your log.
- Use Burp Intruder to cycle through these methods, focusing on low-priority areas to avoid unintended consequences, like a careful explorer avoiding dangerous traps.

**Content Types**:
- APIs often expect data in a specific format. Changing the Content-Type header can:
  - Trigger errors revealing useful information, much like pressing the wrong button in an ancient temple might reveal hidden secrets.
  - Bypass defenses or exploit logic differences, similar to finding a hidden passageway.
- Use the Content type converter BApp to switch between formats like XML and JSON, akin to translating ancient texts.

### Discovering Hidden Endpoints and Parameters

**Using Intruder for Hidden Endpoints**:
- Test structures like `/api/user/update` with Burp Intruder, adding payloads at common positions. Utilize wordlists, much like a treasure hunter uses maps marked with potential dig sites.

**Finding Hidden Parameters**:
- Use Burp Intruder and Param Miner BApp to uncover hidden parameters, and the Content Discovery Tool to find parameters not linked from visible content, like finding hidden switches in a secret room.

### Testing for Vulnerabilities

**Mass Assignment Vulnerabilities**:
- These occur when frameworks automatically bind request parameters to internal object fields. It’s like finding out that a hidden lever not only opens a secret door but also triggers a trap.

**Testing Mass Assignment**:
- Send PATCH requests with parameters like `{"username": "wiener", "email": "wiener@example.com", "isAdmin": false}`. Check responses for unusual behavior, much like testing each step for hidden pressure plates.

**Server-Side Parameter Pollution**:
- This vulnerability lets attackers manipulate server-side requests by injecting parameters into user inputs. It’s like inserting a false clue into a treasure map to mislead others.

  - **Query String Pollution**: Test by inserting characters like `#`, `&`, and `=`, similar to testing different keys in a lock.
  - **Path Traversal**: Test by adding path sequences like `peter/../admin`, akin to finding a hidden path through a maze.

### Testing with Automated Tools

**Burp Scanner and Backslash Powered Scanner**:
- Use Burp Scanner to detect suspicious input transformations, like using a metal detector to find hidden metal objects. The Backslash Powered Scanner BApp helps identify server-side injection vulnerabilities, much like using a spyglass to spot distant dangers.

### Preventing Vulnerabilities

**Design Considerations**:
- **Protect Documentation**: Keep it updated and secure, like safeguarding your treasure map.
- **Validate Inputs**: Use allowlists and blocklists to control input parameters, akin to setting up a security perimeter around your treasure.
- **Error Handling**: Use generic error messages to avoid revealing sensitive information, much like using decoy maps to mislead potential thieves.
- **Versioning**: Apply security measures across all API versions, ensuring that every iteration of your treasure map is secure.

**Preventing Mass Assignment**:
- Allowlist user-updatable properties and blocklist sensitive properties, preventing unintended parameter binding, like ensuring only trusted allies have access to the secret vault.

### Real-World Examples of API Testing Vulnerabilities

1. **Facebook Graph API - Access Token Exposure (2018)**
   - **Incident**: A vulnerability exposed access tokens of 50 million users.
   - **Consequences**: Account takeover, access to private messages, posting updates.
   - **Lesson**: Implement robust token management and regular audits.

2. **Uber API - Personal Data Exposure (2016)**
   - **Incident**: Insufficient access controls exposed personal data of riders and drivers.
   - **Consequences**: Risk of privacy breaches and data misuse.
   - **Lesson**: Ensure strict access controls and regularly update security policies.

3. **Twitter API - Direct Message Leak (2017)**
   - **Incident**: A vulnerability allowed unauthorized access to DMs.
   - **Consequences**: Exposure of private conversations.
   - **Lesson**: Thoroughly test permission systems and authorization checks.

4. **Tesla API - Remote Control of Vehicles (2016)**
   - **Incident**: Researchers accessed and controlled vehicle features remotely.
   - **Consequences**: Significant security risk, potential vehicle theft or manipulation.
   - **Lesson**: Rigorous security testing for critical systems and secure authentication.

5. **GitHub API - Repository Data Exposure (2020)**
   - **Incident**: Unauthorized access to private repository data due to improper token handling.
   - **Consequences**: Exposure of sensitive code and intellectual property.
   - **Lesson**: Use secure token handling methods and regularly rotate tokens.

6. **Slack API - Bypassing Rate Limits (2019)**
   - **Incident**: A vulnerability allowed attackers to bypass rate limits and spam messages.
   - **Consequences**: Denial-of-service attacks, disrupted services.
   - **Lesson**: Implement and enforce rate limiting and monitor API usage patterns.

7. **Google Cloud API - Sensitive Data Leak (2020)**
   - **Incident**: Misconfiguration exposed sensitive data of enterprise customers.
   - **Consequences**: Exposure of sensitive business information.
   - **Lesson**: Ensure proper configuration management and regular security audits.

### Conclusion

Effective API testing is like embarking on an epic quest, requiring a thorough understanding of the API’s structure and behavior. By following these steps, you can identify and mitigate various vulnerabilities, ensuring the security and reliability of your digital treasure. Remember, continuous testing and updating security measures are key to safeguarding against emerging threats.

_Mischief Managed._