API Security testing - Starter kit

API (Application Programming Interface) security testing is an essential part of ensuring the protection of sensitive data and systems. Here are some steps to help you get started with security testing for APIs.

• Understand the API: Before you begin testing, it is important to have a good understanding of the API and how it works. This includes the types of requests and responses, the endpoints, and the parameters that are used.
• Identify the security requirements: Identify the security requirements for the API, including any regulatory compliance that must be met. This will help you focus your testing efforts on the areas that are most important.
• Test for common vulnerabilities: Common vulnerabilities such as SQL injection, cross-site scripting (XSS), and cross-site request forgery (CSRF) should be tested for. There are various tools available to help with this, such as Burp Suite, OWASP ZAP, and Nessus.
• Test for authentication and authorization: Ensure that the API has proper authentication and authorization controls in place. Test for weak or easily guessable credentials, and verify that the API is properly enforcing access controls.
• Test for data validation: Ensure that the API is properly validating input to prevent injection attacks and other malicious input. Use tools like FuzzAPI and Postman to test for this.
• Test for sensitive data exposure: Sensitive data such as credit card numbers and social security numbers should be properly encrypted and not exposed through the API. Test for this by using tools such as OWASP Sensitive Data Discovery.
• Test for performance and scalability: Ensure that the API can handle high traffic and scale as needed. Test for this by using tools such as Apache JMeter and Gatling.
• Keep testing: Security testing should be an ongoing process, as new vulnerabilities and threats are constantly emerging. Keep testing the API to ensure that it remains secure.

Security testing for APIs is an essential part of ensuring the protection of sensitive data and systems. By understanding the API, identifying the security requirements, testing for common vulnerabilities, and testing for authentication and authorization, data validation, sensitive data exposure, performance and scalability, and keeping testing. You will be able to ensure that the API is secure and able to protect sensitive data and systems.

Some sample examples of API security test cases that can be used to test the security of an API are:

1. Authentication test: Verify that the API requires proper authentication and that it is properly enforcing access controls. This can include testing for weak or easily guessable credentials, and attempting to access the API without proper authentication.
2. Authorization test: Verify that the API is properly enforcing access controls, and that a user can only access the resources they are authorized to access. This can include attempting to access resources that a user is not authorized to access, and testing for privilege escalation vulnerabilities.
3. Input validation test: Verify that the API is properly validating input to prevent injection attacks and other malicious input. This can include testing for SQL injection, cross-site scripting (XSS), and cross-site request forgery (CSRF) vulnerabilities.
4. Encryption test: Verify that sensitive data such as credit card numbers and social security numbers is properly encrypted and not exposed through the API. This can include testing for weak encryption algorithms and attempting to intercept sensitive data in transit.
5. Performance and scalability test: Verify that the API can handle high traffic and scale as needed. This can include testing for bottlenecks and resource limitations, and attempting to overload the API with a large number of requests.
6. Security misconfigurations: Verify that the API is properly configured and that there are no misconfigurations that could lead to vulnerabilities. This can include testing for default or easily guessable credentials on the API, servers or databases it communicates with, testing for open ports, and finding misconfigurations of access controls.
7. Data leakage: Verify that data is not being leaked through the API. This can include testing for data leakage through error messages, and testing for data leakage through the API's logs.
8. Vulnerability scanning: Use automated tools to scan the API for known vulnerabilities. This can include using tools such as Burp Suite, OWASP ZAP, and Nessus.

These test cases are just a sample of what can be done for API security testing. Depending on the specific requirements and the complexity of the API, there can be more test cases to be added. Additionally, testing should be an ongoing process, as new vulnerabilities and threats are constantly emerging.

A common security bug that can be found in an API is an SQL injection vulnerability. An SQL injection vulnerability occurs when an attacker is able to insert malicious SQL code into an API endpoint that is not properly sanitized. This can allow the attacker to access or modify sensitive data in the backend database.

For example, consider a simple API endpoint that allows a user to search for a specific product by ID. The endpoint takes the product ID as a parameter and returns information about the product from a database. The API code might look something like this:

GET /api/products/{id}

SELECT * FROM products WHERE id = {id}        

However, if the API is not properly sanitizing the input, an attacker could insert malicious SQL code into the id parameter. For example, an attacker could insert the following code into the id parameter:

1 OR 1=1        

The resulting SQL query would be:

SELECT * FROM products WHERE id = 1 OR 1=1        

This query would return all the rows of the table, potentially exposing sensitive data to the attacker.

To fix this, use parameterized queries or prepared statements to ensure that input is properly sanitized before being included in the query. This would prevent the attacker from injecting malicious SQL code into the query, and would ensure that only the intended data is returned.

Authentication testing for an API involves verifying that the API requires proper authentication and that it is properly enforcing access controls. Here is an example of an authentication test for an API:

1. Test for missing or weak authentication: Attempt to access the API without providing any authentication credentials or providing easily guessable credentials such as "admin:password" or "test:test". If the API allows access without proper authentication or with weak credentials, it is considered a failure.
2. Test for broken authentication and session management: Attempt to access the API using stolen or guessing session tokens, cookies, or API keys. If the API allows access with stolen or guessed credentials, it is considered a failure.
3. Test for authentication bypass: Attempt to access the API by bypassing the authentication mechanism. This could include attempting to access the API using a different endpoint or by manipulating the authentication parameters. If the API allows access by bypassing the authentication mechanism, it is considered a failure.
4. Test for weak password policy: Attempt to set weak passwords for the API and check if the API accepts them. If the API accepts weak passwords, it is considered a failure.
5. Test for Multi-factor authentication: Attempt to access the API by providing only one factor of authentication, and check if the API allows access. Multi-factor authentication is considered to be an additional layer of security, so if the API allows access with only one factor of authentication, it is considered a failure.
6. Test for session timeout: Attempt to access the API with an expired session token, and check if the API allows access. If the API allows access with an expired session token, it is considered a failure.

Authorization testing for an API involves verifying that the API is properly enforcing access controls, and that a user can only access the resources they are authorized to access. Here is an example of an authorization test for an API:

1. Test for missing or broken access controls: Attempt to access resources that a user is not authorized to access. This can include attempting to access sensitive data, modifying or deleting data, or performing administrative tasks. If the API allows access to unauthorized resources, it is considered a failure.
2. Test for privilege escalation: Attempt to elevate a user's privileges by exploiting vulnerabilities in the access controls. This can include attempting to bypass authentication or access controls, or attempting to impersonate other users. If the API allows privilege escalation, it is considered a failure.
3. Test for weak or easily guessable resource IDs: Attempt to access resources by guessing or using easily guessable resource IDs, such as sequential or incremental numbers. If the API allows access to resources using easily guessable IDs, it is considered a failure.
4. Test for insecure direct object references: Attempt to access resources by manipulating the resource ID in the request. If the API allows access to resources by manipulating the resource ID, it is considered a failure.
5. Test for least privilege: Attempt to access resources that a user does not need to access to perform their job. This can include attempting to access sensitive data, modifying or deleting data, or performing administrative tasks. If the API allows access to unnecessary resources, it is considered a failure.
6. Test for role-based access controls: Attempt to access resources that a user is not authorized to access based on their role. This can include attempting to access sensitive data, modifying or deleting data, or performing administrative tasks. If the API allows access to resources based on a user's role, it is considered a failure.

Input validation testing for an API involves verifying that the API is properly validating input to prevent injection attacks and other malicious input. Here is an example of an input validation test for an API:

1. Test for SQL injection: Attempt to insert malicious SQL code into input parameters, such as by adding a single quote (') to a text field. If the API does not properly sanitize the input and allows the SQL code to be executed, it is considered a failure.
2. Test for Cross-site scripting (XSS): Attempt to insert malicious JavaScript code into input parameters, such as by adding <script> tags to a text field. If the API does not properly sanitize the input and allows the JavaScript code to be executed, it is considered a failure.
3. Test for Cross-site request forgery (CSRF): Attempt to perform actions on the API using a forged request, such as by tricking a user into clicking a link or submitting a form. If the API does not properly validate the origin of the request and allows the forged request to be executed, it is considered a failure.
4. Test for Command injection: Attempt to insert malicious commands into input parameters, such as by adding shell commands or scripts to a text field. If the API does not properly sanitize the input and allows the command to be executed, it is considered a failure.
5. Test for File inclusion: Attempt to access restricted files by manipulating input parameters, such as by adding file paths to a text field. If the API does not properly validate the input and allows access to restricted files, it is considered a failure.
6. Test for Buffer overflow: Attempt to cause buffer overflow by sending oversized inputs to the API. If the API does not properly validate the input and allows buffer overflow, it is considered a failure.
7. Test for Regex injection: Attempt to insert malicious Regular Expressions into input parameters, such as by adding a Regex that can cause a Denial of Service(DoS) attack. If the API does not properly sanitize the input and allows the Regular Expression to be executed, it is considered a failure.

Encryption testing for an API involves verifying that sensitive data such as credit card numbers and social security numbers is properly encrypted and not exposed through the API. Here is an example of an encryption test for an API:

1. Test for weak encryption algorithms: Attempt to access the sensitive data by using weak encryption algorithms. For example, attempting to decrypt data that is encrypted using the outdated Data Encryption Standard (DES) algorithm.
2. Test for encryption in transit: Attempt to intercept sensitive data in transit by intercepting the API's network traffic. For example, by using tools such as Wireshark and Burp Suite to capture the network traffic and analyze it for sensitive data.
3. Test for encryption at rest: Attempt to access sensitive data that is stored on the server by attempting to access the server's file system or database. For example, by attempting to access the data through SQL injection or by guessing or stealing the server's credentials.
4. Test for key management: Attempt to access sensitive data by attempting to gain access to the encryption keys. For example, by attempting to guess or steal the encryption keys, or attempting to access the keys through a vulnerability in the key management system.
5. Test for data leakage: Attempt to access sensitive data by attempting to access the API's logs, error messages, and other output. For example, by attempting to access sensitive data through the API's error messages or by attempting to access sensitive data that is stored in the API's logs.
6. Test for forward secrecy: Attempt to access sensitive data by attempting to decrypt previously captured traffic by guessing or stealing encryption keys.
7. Test for Perfect Forward Secrecy: Attempt to access sensitive data by attempting to decrypt previously captured traffic by guessing or stealing encryption keys.
8. Test for certificate validation: Attempt to access sensitive data by attempting to use invalid or self-signed certificates, or by attempting to intercept the communication with a man-in-the-middle attack.

An example of an encryption bug in an API:

An API for a banking application that allows users to access their account information and make transactions. The API encrypts sensitive data, such as account numbers and passwords, using the Advanced Encryption Standard (AES) algorithm with a fixed key. A vulnerability in the API's encryption implementation is discovered that allows an attacker to determine the encryption key used by the API. This can be done by analyzing the API's network traffic or by exploiting a vulnerability in the encryption algorithm.

Once the encryption key is determined, an attacker can easily decrypt the sensitive data and access sensitive information such as account numbers and passwords.

To prevent this, use a unique key for each user, and store the key in a secure location such as a Hardware Security Module (HSM), and use a key rotation mechanism that changes the key frequently. Additionally, using a more secure encryption algorithm such as Galois/Counter Mode (GCM) instead of AES in ECB mode would have avoided this vulnerability.

Example of a bug found in a real-world API: "Heartbleed" vulnerability in the OpenSSL library: This vulnerability affected many websites and services that used OpenSSL to encrypt sensitive data such as passwords and credit card numbers.

The vulnerability was caused by a flaw in the OpenSSL's implementation of the Heartbeat extension, which allows a client to send a "ping" message to the server to keep the connection alive. The vulnerability allowed an attacker to send a maliciously crafted Heartbeat request that caused the server to return a large amount of memory, potentially including sensitive information such as private encryption keys.

Data leakage is a bug that occurs when sensitive data is inadvertently exposed through an API. Here is an example of a data leakage bug in an API:

1. A sample API for a medical records system that allows doctors and nurses to access patient information. The API is designed to encrypt sensitive data such as patient names, addresses, and medical history.
2. A vulnerability is discovered that allows an attacker to access sensitive data by manipulating the API's parameters. For example, by modifying the API's URL to access patient records, an attacker could potentially access sensitive data such as medical history, medications, and personal information.
3. An attacker could also potentially access sensitive data by exploiting a vulnerability in the API's error handling. For example, if the API returns detailed error messages when it encounters an error, an attacker could potentially use that information to access sensitive data.
4. An example of a fix would be to prevent sensitive data from being included in error messages, or to limit the amount of data that is returned in error messages. Additionally, implementing proper input validation, security controls and logging mechanisms can also help to mitigate data leakage vulnerabilities.

Conclusion: Software security testing is becoming more and more important as cyber attacks and data breaches become more frequent and sophisticated.

One trend in software security testing is the increased use of automation and machine learning techniques to improve the efficiency and effectiveness of testing. This includes techniques such as fuzz testing, which automatically generates large numbers of inputs to test for vulnerabilities, and dynamic application security testing (DAST), which automatically scans web applications for vulnerabilities.

Another trend is the shift towards DevSecOps, which is the integration of security testing into the software development process. This allows security testing to be done early and often, reducing the risk of vulnerabilities being discovered later in the development process.

Additionally, with the increasing number of companies moving to the cloud and utilizing cloud services, cloud security testing has become a critical aspect of software security testing. It is important to ensure that the cloud infrastructure and services are configured securely and that data is protected while in transit and at rest.

Overall, software security testing is a rapidly evolving field, and it's important for testers to stay up-to-date with the latest developments and best practices to ensure their software and systems are secure. Ensuring secure APIs is one of the best and easiest ways to prevent damages and avoid financial losses for companies.