Web Security Interview Questions and Answers

1. What is Cross-Site Scripting (XSS)?

   • Answer: Cross-Site Scripting (XSS) is a type of security vulnerability that allows an attacker to inject malicious scripts into otherwise benign and trusted websites. These scripts can then be executed in the victim's browser, potentially stealing cookies, session tokens, or other sensitive information. There are three main types: Reflected XSS, Stored XSS, and DOM-Based XSS. Prevention involves input sanitization, output encoding, and using a Content Security Policy (CSP).

2. What is SQL Injection?

   • Answer: SQL Injection is a code injection technique that exploits vulnerabilities in database interactions. Attackers inject malicious SQL code into input fields, manipulating database queries to retrieve sensitive data, modify or delete data, or even execute arbitrary commands on the database server. Prevention strategies include parameterized queries (prepared statements), input validation, and using an ORM (Object-Relational Mapper).

3. Explain the concept of Cross-Site Request Forgery (CSRF).

   • Answer: Cross-Site Request Forgery (CSRF) is an attack that tricks a user into performing an unwanted action on a web application in which they're currently authenticated. It leverages the user's existing session to make unauthorized requests. For example, an attacker might create a link that submits a form on the victim's banking website, transferring funds without their knowledge. Prevention involves using anti-CSRF tokens, verifying HTTP Referer headers (though unreliable), and employing double-submit cookies.

4. What is a Denial of Service (DoS) attack?

   • Answer: A Denial of Service (DoS) attack aims to make a machine or network resource unavailable to its intended users. This is achieved by overwhelming the target with a flood of traffic or requests, rendering it unresponsive. Distributed Denial of Service (DDoS) attacks involve multiple compromised systems (bots) attacking a single target.

5. What are HTTP headers and how are they relevant to security?

   • Answer: HTTP headers are key-value pairs that accompany HTTP requests and responses. They provide metadata about the request or response, such as the content type, caching directives, and authentication information. From a security perspective, headers like `X-Frame-Options` (to prevent clickjacking), `Content-Security-Policy` (CSP), `Strict-Transport-Security` (HSTS), and `X-XSS-Protection` play crucial roles in mitigating various web vulnerabilities.

6. What is session hijacking?

   • Answer: Session hijacking is a type of attack where an attacker steals a user's active session ID to gain unauthorized access to the user's account and data. This can be done through various methods, including exploiting XSS vulnerabilities, sniffing network traffic, or exploiting weak session management practices.

7. Explain the importance of input validation.

   • Answer: Input validation is crucial for preventing various web vulnerabilities, including SQL injection, XSS, and command injection. By rigorously validating and sanitizing all user inputs before using them in database queries or displaying them on a webpage, developers significantly reduce the risk of attacks.

8. What is a Man-in-the-Middle (MITM) attack?

   • Answer: A Man-in-the-Middle (MITM) attack occurs when an attacker secretly relays and possibly alters the communication between two parties who believe they are directly communicating with each other. This can be used to intercept sensitive information, such as passwords or credit card details.

9. What is the purpose of a Content Security Policy (CSP)?

   • Answer: A Content Security Policy (CSP) is a security mechanism that allows web developers to control the resources the browser is allowed to load for a given page. It helps mitigate XSS attacks by specifying allowed sources for scripts, stylesheets, images, and other resources. This reduces the risk of attackers injecting malicious content.

10. What is HTTPS and why is it important for security?

    • Answer: HTTPS (Hypertext Transfer Protocol Secure) is an extension of HTTP that uses TLS/SSL to encrypt communication between a web browser and a server. This encryption protects sensitive data, such as passwords and credit card information, from being intercepted by eavesdroppers. It also verifies the server's identity through SSL certificates, preventing man-in-the-middle attacks.

11. What is a zero-day exploit?

    • Answer: A zero-day exploit is an attack that takes advantage of a previously unknown vulnerability in software. Because the vulnerability is unknown, there is no patch available, making it particularly dangerous.

12. Explain the concept of authentication and authorization.

    • Answer: Authentication is the process of verifying the identity of a user or system. Authorization is the process of determining what a user or system is allowed to access after authentication. They are distinct but related security concepts. Authentication confirms "who" you are, while authorization determines "what" you can do.

13. What are some common web application firewalls (WAFs)?

    • Answer: Some popular WAFs include AWS WAF, Cloudflare WAF, Akamai Kona Site Defender, and Imperva Incapsula. They filter malicious traffic and protect web applications from various attacks.

14. How does OAuth 2.0 work?

    • Answer: OAuth 2.0 is an authorization framework that allows third-party applications to access resources on a user's behalf without sharing their credentials. It works by using access tokens and refresh tokens to grant temporary access to specific resources, improving security compared to directly sharing passwords.

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