What techniques are used to eliminate and prevent vulnerabilities in security systems?

The following techniques are used to eliminate and prevent vulnerabilities in security systems:

• Validation and sanitization of input data — prevents SQL injections, XSS, and other attacks.
• Use of secure libraries and frameworks — which already consider best security practices.
• Authentication and authorization — reliable access management, storing passwords with hashing (e.g., bcrypt).
• Data encryption — both at rest and in transit (TLS/SSL).
• Error handling and logging — without revealing sensitive information.
• Regular updates of dependencies and patches — to close known vulnerabilities.
• Use of static and dynamic code analysis — to identify potential issues.

Example of input validation in Python:

import re

def is_valid_username(username):
    # Allow only letters, digits, and underscores
    return re.match(r'^\w{3,20}$', username) is not None

user_input = "user_123"
if is_valid_username(user_input):
    print("Username is valid")
else:
    print("Invalid username")