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of 28What is input validation and why is it crucial for application security?
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Input validation is the process of verifying that user-supplied data meets expected criteria before processing it. It's crucial because unvalidated input is the root cause of many security vulnerabilities including injection attacks, buffer overflows, and data corruption.
Key principles:
- Whitelist validation: Define what is acceptable rather than what isn't
- Server-side validation: Never rely solely on client-side validation
- Sanitization: Clean or encode input when validation isn't sufficient
- Length limits: Prevent buffer overflows and DoS attacks
Example of proper validation:
import re
def validate_email(email):
pattern = r'^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$'
if re.match(pattern, email) and len(email) <= 254:
return True
return False
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What's the difference between authentication and authorization?
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Authentication verifies "who you are" - confirming the identity of a user or system.
- Examples: Username/password, biometrics, certificates
Authorization determines "what you can do" - granting or denying access to resources based on identity.
- Examples: Role-based access control (RBAC), permissions, ACLs
Example flow:
- User provides credentials (authentication)
- System verifies credentials
- System checks user's permissions for requested resource (authorization)
- Grant or deny access based on permissions
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What is SQL injection and how can it be prevented?
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SQL injection occurs when user input is directly concatenated into SQL queries, allowing attackers to manipulate the database.
Example of vulnerable code:
# VULNERABLE
query = f"SELECT * FROM users WHERE username = '{username}'"
Attack example: username = "admin'; DROP TABLE users; --"
Prevention methods:
- Parameterized queries/Prepared statements (most effective)
- Stored procedures (when properly implemented)
- Input validation (whitelist approach)
- Least privilege principle for database accounts
- Web Application Firewalls (additional layer)
Secure example:
# SECURE - Using parameterized query
cursor.execute("SELECT * FROM users WHERE username = %s", (username,))
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What is XSS and what are the three main types?
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Cross-Site Scripting (XSS) allows attackers to inject malicious scripts into web pages viewed by other users.
Three main types:
Stored XSS (Persistent): Malicious script stored on server
- Example: Comment section storing
<script>alert('XSS')</script>
- Example: Comment section storing
Reflected XSS (Non-persistent): Script reflected from request
- Example: Search parameter displayed without encoding
DOM-based XSS: Vulnerability in client-side JavaScript
- Example:
document.write(location.hash.substring(1))
- Example:
Impact: Session hijacking, credential theft, defacement, malware distribution
Prevention: Input validation, output encoding, Content Security Policy (CSP), sanitization
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What is CSRF and how can it be prevented?
What's the difference between hashing, encryption, and encoding?
What is the OWASP Top 10 and how does it guide secure development?
Explain the difference between input validation, sanitization, and encoding.
What are the security considerations when implementing password-based authentication?
Explain JWT (JSON Web Tokens) and their security implications.
What are the different types of SQL injection attacks?
How do you prevent XSS attacks in web applications?
Explain the different CSRF token implementation patterns.
What are the security best practices for session management?
What are the key principles of secure cryptographic implementation?
How should applications handle errors securely?
What are the key security considerations for REST API design?
What are the security risks associated with file uploads and how do you mitigate them?
Explain the principle of least privilege and how to implement it.
What are some common input validation bypass techniques that attackers use?
How do prepared statements prevent SQL injection, and what are their limitations?
What is Content Security Policy (CSP) and how does it help prevent XSS?
What is session fixation and how do you prevent it?
Explain the security considerations when implementing HTTPS/TLS.
What are the security considerations for application logging?
How do you implement secure API rate limiting?
What are the security implications of poor memory management in applications?
What is defense in depth and how do you implement it in web applications?
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