Can Security Testing be Trusted to TDD?

Imagine the situation: you are developing a web application for processing payments. Your team has decided to use TDD to create clean, efficient code. After launching the application, you receive reports of suspicious transactions. You discover a vulnerable area through which attackers could gain unauthorized access to sensitive information.

With tests written within TDD, you quickly identify the location of the vulnerability and create a fix. But an important question arises: can TDD security testing be trusted entirely?

Let's find out!

1. How to implement Test Driven Development?

Incorporating security testing into the Test-Driven Development (TDD) process requires a careful and thoughtful approach. Below are the main steps that will tell you how to do this.

1. Determine your security requirements

The first step should be to determine the security requirements for your application. This should include an understanding of potential threats, attack vectors and necessary protective measures.

2. Develop test cases for security

Once the security requirements are defined, you must develop test cases that effectively test those requirements. This may include testing for vulnerabilities such as SQL injections, cross-site scripting (XSS), and other types of attacks.

test('SQL Injection protection', () => {

??const userInput = "'; DROP TABLE users; --";

??expect(() => {

????db.query(`SELECT * FROM users WHERE id = '${userInput}'`);

??}).not.toThrow();

});

In this example, we verify that our database query function handles SQL injection attempts correctly and does not throw an exception.

3. Write code that passes security tests

Now that you have your security tests, the next step is to write code that passes those tests. This may require the use of various security strategies such as input sanitization, use of parameterized queries, etc.

function queryDatabase(query, params) {

??// Using parameterized query to prevent SQL injection

??return db.query(query, params);

}

4. Carry out the refactoring process

After you've written code that passes security tests, you should refactor it to improve the code's readability and maintainability. At this point, it is important to ensure that the refactoring process does not affect the security measures implemented in the previous step.

Applying TDD to security testing can provide many benefits, including greater confidence in the security of your code and the ability to quickly discover and fix vulnerabilities. However, it is worth noting that TDD cannot replace all types of security testing. For example, many types of security threats, such as distributed denial of service (DDoS) or Man-in-the-Middle attacks, are difficult to model using a TDD approach. Therefore, TDD should only be one part of your security testing strategy.

2. Best practices for combining TDD and security testing

Using best practices and the right tools is essential to successfully combining Test-Driven Development (TDD) and security testing. Let's look at this in more detail.

1. Test development based on security requirements

Your security tests should focus on testing the specific security requirements of your application. For example, if you know that your application is susceptible to SQL injection, you should write tests that specifically check for this type of threat.

test('SQL Injection protection', () => {

??const userInput = "'; DROP TABLE users; --";

??const query = SELECT * FROM users WHERE id = '${userInput}';

??expect(() => db.query(query)).not.toThrow();

});

In this example, the test verifies that the application resists SQL injection and does not cause an error during the query.

2. Using automated security testing tools

Tools like OWASP ZAP (Zed Attack Proxy) или Burp Suite, can be very useful for automating parts of the security testing process. These tools can automatically scan your application for common vulnerabilities such as XSS or CSRF attacks.

Example with OWASP ZAP:

#run ZAP using CLI

zap.sh -quickurl https://your-web-app.com

Here we use ZAP to automatically scan our web application for common vulnerabilities.

3. Regular update and review of security tests

As your application evolves and security requirements change, it is important to periodically review and update your security tests. This can help detect new threats and ensure that your application continues to meet all security requirements.

4. Apply security by default principles to your code

When writing code that must pass security tests, you should adhere to the principles of "security by default." This means that you should design your application in such a way that the system settings are secure by default.

For example, when using Express.js you can use middleware like helmet, to set various HTTP headers that will help protect your application.

var express = require('express');

var helmet = require('helmet');

var app = express();

app.use(helmet()); // use helmet middleware for security

5. Training and safety awareness

Ensuring ongoing training and security awareness among your development team is critical. Resources such as OWASP Cheat Sheets, can be very useful in educating developers about general security principles and threats.

Together with these strategies, applying TDD to security testing can significantly improve the security posture of your application, allowing you to discover and fix vulnerabilities faster.

3. TDD and Security Testing: Dispelling the Myths

When it comes to combining TDD and security testing, there are some misconceptions that can affect the perception and adoption of this approach. Let's dispel some of these myths.

Myth 1: TDD is not suitable for security testing

This approach may arise because TDD is traditionally used to ensure code quality rather than security. However, TDD can be a tool for any type of testing, including security. After all, the basis of TDD is writing tests before the code itself, and these tests can be built around any requirements, including security requirements.

Myth 2: TDD is too expensive for security testing

TDD can take some time in the initial stages of development because it requires writing tests before implementing features. However, this investment of time can pay off in the long run because it helps identify and fix security vulnerabilities earlier in development, when bug fixes are typically cheaper.

Myth 3: TDD provides complete security

Although TDD can help detect and resolve security vulnerabilities, it should be remembered that it cannot provide 100% security. Security is a process, and it requires the use of various techniques and tools, including, but not limited to, manual testing, penetration testing, and security audits.

Myth 4: TDD is too complex to be used in security testing

Although TDD may seem difficult for beginners, with practice it becomes part of the natural development process. In addition, many tools and libraries make writing tests easier and more convenient. For example, frameworks such as Jest for JavaScript provide a simple and intuitive API for writing tests.

Although TDD takes time and effort to implement correctly, it can be a valuable tool in your security testing arsenal. With a proper understanding of its strengths and weaknesses, you can use TDD to create more secure applications.

4. Case study: TDD and security testing in an Express.js application

Imagine you are developing a Node.js based web application using Express.js. Your application includes user registration functionality, and you need to ensure that this functionality is secure and not susceptible to vulnerabilities such as SQL injection. Your development approach is based on TDD principles.

Step 1: Determine Security Requirements

The first step is to determine the security requirements for the logging function. You need to ensure that user input is processed securely and does not allow SQL injection.

Step 2: Develop Security Tests

You then develop security tests that test these features. For our purposes, you can use the Jest testing library.

const request = require('supertest');

const app = require('../app');

test('User registration should be safe from SQL Injection', async () => {

????const userInput = "'; DROP TABLE users; --";

????const response = await request(app)

????????.post('/users/register')

????????.send({ username: userInput, password: 'password' });

????

????expect(response.status).toBe(400);

});

In this test, we use supertest to send a user registration request with a dangerous string that can cause SQL injection. We then verify that our application returns a response status of 400 (Bad Request), indicating that it is handling this situation correctly.

Step 3: Write code that passes security tests

Now that you have a security test, your job will be to write code that passes that test. In our case, we will use a parameterized SQL query to avoid SQL injection vulnerability.

app.post('/users/register', (req, res) => {

??const { username, password } = req.body;

??const query = 'INSERT INTO users (username, password) VALUES (?, ?)';

??db.query(query, [username, password], (err) => {

????if (err) {

??????res.status(400).send('Bad Request');

????} else {

??????res.status(200).send('User registered successfully');

????}

??});

});

Step 4: Refactor and repeat tests

After writing code that passes security tests, refactoring should be done to improve the structure and readability of the code. After refactoring, it is important to re-run the tests to ensure that the changes do not affect the security of the application.

This case study demonstrates how security testing can be implemented into the TDD process. Although this is a simplified example, it shows that TDD can be a powerful tool for improving the security of your application.

Conclusion

Is TDD enough to ensure application security? No. But this does not mean that TDD has no value in a security context.

TDD keeps code clean and prevents common vulnerabilities. Tests written within TDD are useful for quickly identifying and fixing vulnerabilities, as proven in our technical case study.

However, TDD is not a panacea and cannot replace all types of security testing. Many more complex threats and vulnerabilities, such as man-in-the-middle attacks and DDoS attacks, require deeper investigation.

To effectively use TDD in a security context, developers must be well aware of possible security threats and how those threats can be modeled within TDD. Tools and resources such as OWASP ZAP and OWASP Cheat Sheets can be useful in this context.

TDD has its place in the security testing toolkit, but it should not be used as the only approach to securing an application. Only a comprehensive strategy that includes various security testing methods can adequately protect your application from a variety of threats.