API Security 101 for Developers: How to Easily Secure Your APIs

Debra Hopper
March 29, 2023
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Application Programming Interfaces (APIs) are a fundamental component of modern software development. APIs allow developers to integrate different software systems, making it easier than ever to create complex applications and services. However, as with any software component, APIs are also prone to security vulnerabilities that can be exploited by attackers. 

API security is an ongoing process that demands continual attention and effort from everyone on the development team. However, with the right knowledge and tools, developers can design, build, and test secure APIs without adding to their workload.

In the following sections, we will discuss: 

  1. API Basics
  2. Common API Security Vulnerabilities
  3. Best Practices for API Security
  4. How to do API Security Automatically

By the end of this blog post, you will have a good understanding of API security and the steps you can take to easily secure your APIs.

API Basics: What Is an API and How Do APIs Work?

As a developer, you've likely encountered APIs in your work, and may even use them regularly in your projects. But for those new to the world of APIs, lets cover the basics:

What is an API?

An Application Programming Interface (API) is a set of protocols, routines, and tools used by developers to build software applications. APIs offer a standard method for software components to communicate with one another. This makes it possible for developers to connect different software systems without having to understand the details of each system.

How do APIs work?

In simpler terms, APIs allow developers to access data or functionality from one application or service and use it in another application or service. For example, a developer building a mobile app that displays weather information might use an API provided by a weather service to retrieve the current weather conditions and display them in the app.

APIs can be divided into two broad categories: internal and external. Internal APIs are used within an organization to share data and functionality between different software systems. External APIs are accessible to users outside of an organization. They allow third-party developers to access an organization's software data or functions.

Examples of Popular APIs

Some popular examples of external APIs include the Twitter API, the Google Maps API, and the Facebook API. These APIs allow developers to access data and functionality provided by these services and integrate them into their own applications or services. 

For example, the Google Maps API allows developers to integrate Google Maps into their own applications or websites. This gives them an easy way to build custom maps and add location-based features to their applications or websites. For example, a real estate website could use the Google Maps API to display the location of each property on a map. Or, a delivery app could use the API to calculate the best route between two locations.

In the next section, we will discuss common API security vulnerabilities that developers need to be aware of.


Common API Security Vulnerabilities

While APIs are useful for integrating software systems, they can also introduce security vulnerabilities that can be exploited by attackers. The most common API security vulnerabilities that developers need to be aware of are:

Injection Attacks

Injection attacks occur when an attacker sends malicious data to an API endpoint that can be interpreted as code by the server. This can allow the attacker to execute commands on the server, access sensitive data, or even take control of the server.

For example, an SQL injection is a type of injection attack that occurs when an attacker sends malicious SQL statements to an API endpoint that interacts with a database. If the API does not properly validate and sanitize user input, the attacker can execute arbitrary SQL statements on the database.

Broken Authentication and Session Management 

Authentication is the process of verifying the identity of a user or system. Session management is the process of managing user sessions once they are authenticated. Broken authentication and session management vulnerabilities can allow attackers to impersonate legitimate users and access sensitive data or functionality.

For example, weak or predictable passwords make your APIs vulnerable. An attacker can use brute force attacks to guess the password and gain access to the system. Similarly, APIs need to use strong session identifiers and properly expire user sessions. If this is not done, an attacker can hijack a legitimate user's session and gain access to the system.

Cross-Site Scripting (XSS) 

Cross-Site Scripting (XSS) attacks occur when an attacker injects malicious code into a web page that is viewed by other users. This code is typically in the form of JavaScript that executes in the user's browser and can be used to steal sensitive information or perform other malicious activities.

API-based XSS attacks involve exploiting vulnerabilities in the APIs used by web applications to fetch and display data. An attacker can craft a malicious query that includes a script tag with JavaScript code that steals the user's session token, allowing the attacker to impersonate the user and perform actions on their behalf.

To prevent XSS attacks, web developers must sanitize user input and validate it on the server side. Additionally, they should use content security policies (CSPs) to limit the sources of scripts and other resources that can be loaded by the browser.

Cross-Site Request Forgery (CSRF) 

Cross-site request forgery (CSRF) occurs when an attacker tricks a victim into performing an action on an API endpoint without their knowledge or consent. This can allow the attacker to perform actions on the victim's behalf, such as making unauthorized purchases or changing the victim's account settings.

For example, if an API does not use CSRF tokens to validate requests, an attacker can create a malicious web page that sends unauthorized requests to the API endpoint when a victim visits the page.

Insufficient Encryption and Transport Layer Protection

APIs that transmit sensitive data, such as user credentials or payment information, need to use encryption and transport layer protection to ensure that the data is not intercepted or modified by attackers.

For example, if an API does not use HTTPS to encrypt traffic or uses weak encryption algorithms, an attacker can intercept and modify API requests or responses.

Developer Best Practices for API Security: How to Prevent Common API Vulnerabilities

There are a number of steps developers can take to prevent the common API security vulnerabilities discussed in the previous section, including:

Follow the Principle of Least Privilege

Development teams should always follow the principle of least privilege. API access should be limited to only what is necessary for a given user or system. This means that users should only be able to access the data and functionality that they need to perform their tasks. 

For example, a user who only needs to view data should not have write access to the data. Limiting API access in this way reduces the risk of unauthorized access and data breaches.

Use Strong and Secure Authentication and Authorization Mechanisms

Authentication is the process of verifying the identity of a user or application attempting to access an API. Authorization is the process of determining whether a user or application has the necessary permissions to perform a specific action or access a specific resource. Authentication and authorization are critical to API security, as they ensure that only authorized users or applications can access sensitive data.

One common method of authentication and authorization is the use of OAuth 2.0. OAuth 2.0 is an open standard for authorization. It allows third-party applications to access a user's data without the user sharing their credentials. Instead, the user grants the application access to their data using an access token.

Implement Access Control Mechanisms

Access control is the process of determining who has access to a specific resource or API endpoint. Access control is important for API security, as it ensures that only authorized users or applications can access sensitive data.

One common method of access control is role-based access control (RBAC). RBAC is a method of access control that restricts access based on the roles of individual users within an organization. For example, a developer building an API for a financial institution might use RBAC to ensure that only authorized employees can access customer financial data.

Use Secure Passwords and Password Policies

Strong passwords and password policies are essential to prevent brute force attacks and other password-related vulnerabilities. Password policies should enforce password complexity, minimum password length, and password expiration. Developers should also consider implementing passwordless authentication methods such as biometric authentication to improve the security of their APIs.

Validate and Sanitize All User Input

Input validation ensures that data is in the correct format and meets specific criteria. Input sanitization removes any malicious content from user input. Using input validation and sanitization libraries and frameworks reduces the risk of security vulnerabilities such as SQL injection and cross-site scripting (XSS) attacks.

Use Encryption and Hashing

Encryption is the process of encoding data so that only authorized users can read it. Hashing is the process of transforming data into a fixed-length string of characters. Developers should use encryption to protect sensitive data such as passwords, credit card information, and personal information.

One common method of encryption is Transport Layer Security (TLS). TLS is a protocol that encrypts data as it is transmitted between a client and a server. For example, a developer building an API for an e-commerce site might use TLS to encrypt customer credit card information as it is transmitted between their browser and server.

Rate Limiting

Rate limiting is the process of limiting the number of requests that a user or application can make to an API within a specified time period. Rate limiting prevents denial-of-service (DoS) attacks and ensures that the API is available to all users.

For example, a developer building an API for a weather application might implement rate limiting to ensure that one user cannot make an excessive number of requests in a short period of time, which could cause the API to become unavailable for other users.

Implement Secure Session Management

Session management is essential to prevent session hijacking and other attacks. Secure session management mechanisms such as secure cookies, session timeouts, and re-authentication can help prevent attackers from hijacking user sessions.

Regularly Test for Security Vulnerabilities

It's important to test your API for vulnerabilities regularly, including before you ship code to production and throughout the development process. API security testing tools perform a variety of tests to identify security vulnerabilities. These tests include vulnerability scanning, SQL injection testing, cross-site scripting (XSS) testing, and broken authentication and session management testing. 

By using these tools, developers can identify and address security vulnerabilities before they can be exploited by attackers. This can help prevent data breaches, unauthorized access to sensitive data, and other security incidents. Additionally, using API security testing tools can help ensure compliance with security regulations and standards. 

Put Your API Security on Autopilot

As you can see, API security requires a lot of work and consideration from developers. And even when following best practices, it's impossible to prevent all vulnerabilities. That’s why APIs should be regularly tested for security vulnerabilities. The easiest way for developers to do this is to use an automated API testing tool that integrates directly into their existing development process. 

Mayhem is a security testing solution that we built specifically for developers. It runs continuously in the background and eliminates the need for manual test generation, putting your API security on autopilot. Try it free for 30 days.

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