Senior Security Engineer Interview Questions and Answers

# Example: Secure API design
from functools import wraps
from flask import request, abort
import jwt

def require_auth(f):
    @wraps(f)
    def decorated(*args, **kwargs):
        token = request.headers.get('Authorization')
        if not token:
            abort(401)
        
        try:
            payload = jwt.decode(token, SECRET_KEY, algorithms=['HS256'])
            # Rate limiting
            if check_rate_limit(payload['user_id']):
                abort(429)
            # Authorization
            if not has_permission(payload['user_id'], request.path):
                abort(403)
        except jwt.InvalidTokenError:
            abort(401)
        
        return f(*args, **kwargs)
    return decorated

@app.route('/api/sensitive-data')
@require_auth
def get_sensitive_data():
    # Audit logging
    log_access(request.user_id, 'sensitive-data', 'read')
    return jsonify(data)

# CSPM automation example
import boto3
from datetime import datetime

class AWSSecurityPosture:
    def __init__(self):
        self.ec2 = boto3.client('ec2')
        self.s3 = boto3.client('s3')
        self.iam = boto3.client('iam')
        self.findings = []
    
    def check_s3_encryption(self):
        """Check S3 bucket encryption"""
        buckets = self.s3.list_buckets()['Buckets']
        
        for bucket in buckets:
            bucket_name = bucket['Name']
            try:
                encryption = self.s3.get_bucket_encryption(
                    Bucket=bucket_name
                )
            except:
                self.findings.append({
                    'severity': 'high',
                    'resource': bucket_name,
                    'issue': 'S3 bucket not encrypted',
                    'remediation': 'Enable default encryption'
                })
    
    def check_security_groups(self):
        """Check for overly permissive security groups"""
        sgs = self.ec2.describe_security_groups()['SecurityGroups']
        
        for sg in sgs:
            for rule in sg.get('IpPermissions', []):
                for ip_range in rule.get('IpRanges', []):
                    if ip_range.get('CidrIp') == '0.0.0.0/0':
                        self.findings.append({
                            'severity': 'critical',
                            'resource': sg['GroupId'],
                            'issue': f"Security group allows 0.0.0.0/0 on port {rule.get('FromPort')}",
                            'remediation': 'Restrict source IP ranges'
                        })
    
    def check_iam_policies(self):
        """Check for overly permissive IAM policies"""
        users = self.iam.list_users()['Users']
        
        for user in users:
            policies = self.iam.list_attached_user_policies(
                UserName=user['UserName']
            )['AttachedPolicies']
            
            for policy in policies:
                if policy['PolicyName'] == 'AdministratorAccess':
                    self.findings.append({
                        'severity': 'high',
                        'resource': user['UserName'],
                        'issue': 'User has AdministratorAccess',
                        'remediation': 'Apply least privilege principle'
                    })
    
    def generate_report(self):
        self.check_s3_encryption()
        self.check_security_groups()
        self.check_iam_policies()
        
        return {
            'timestamp': datetime.now().isoformat(),
            'total_findings': len(self.findings),
            'critical': len([f for f in self.findings if f['severity'] == 'critical']),
            'high': len([f for f in self.findings if f['severity'] == 'high']),
            'findings': self.findings
        }

# Pod security context and namespace enforcement
apiVersion: v1
kind: Namespace
metadata:
  name: production
  labels:
    pod-security.kubernetes.io/enforce: restricted
    pod-security.kubernetes.io/audit: restricted
    pod-security.kubernetes.io/warn: restricted
---
apiVersion: v1
kind: Pod
metadata:
  name: api
  namespace: production
spec:
  securityContext:
    runAsNonRoot: true
    seccompProfile:
      type: RuntimeDefault
  containers:
    - name: api
      image: example/api:latest
      securityContext:
        allowPrivilegeEscalation: false
        readOnlyRootFilesystem: true
        capabilities:
          drop: ["ALL"]

# Network Policy for pod isolation
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: deny-all-ingress
  namespace: production
spec:
  podSelector: {}
  policyTypes:
  - Ingress
  - Egress
  ingress: []
  egress:
  - to:
    - namespaceSelector:
        matchLabels:
          name: kube-system
    ports:
    - protocol: UDP
      port: 53

# Secure Lambda function example
import json
import boto3
import os
from aws_xray_sdk.core import xray_recorder
from aws_lambda_powertools import Logger, Tracer

logger = Logger()
tracer = Tracer()

@tracer.capture_lambda_handler
@logger.inject_lambda_context
def lambda_handler(event, context):
    # Input validation
    if 'user_id' not in event:
        return {
            'statusCode': 400,
            'body': json.dumps({'error': 'Missing user_id'})
        }
    
    # Use IAM roles, not hardcoded credentials
    dynamodb = boto3.resource('dynamodb')
    table = dynamodb.Table(os.environ['TABLE_NAME'])
    
    # Least privilege - only access what's needed
    try:
        response = table.get_item(
            Key={'user_id': event['user_id']}
        )
        
        # Don't expose internal errors
        return {
            'statusCode': 200,
            'body': json.dumps(response.get('Item', {}))
        }
    except Exception as e:
        logger.error(f"Error: {str(e)}")
        return {
            'statusCode': 500,
            'body': json.dumps({'error': 'Internal server error'})
        }

# GitLab CI/CD security pipeline
stages:
  - build
  - test
  - security
  - deploy

# SAST scanning
sast:
  stage: security
  script:
    - sonar-scanner \
        -Dsonar.projectKey=myapp \
        -Dsonar.sources=. \
        -Dsonar.host.url=$SONAR_URL
  allow_failure: false

# Dependency scanning
dependency_scan:
  stage: security
  script:
    - npm audit --audit-level=high
    - snyk test --severity-threshold=high
  allow_failure: false

# Container scanning
container_scan:
  stage: security
  script:
    - trivy image --severity HIGH,CRITICAL myapp:latest
  allow_failure: false

# DAST scanning
dast:
  stage: security
  script:
    - zap-baseline.py -t https://staging.example.com
  allow_failure: true

# Automated security checks
class SecurityCodeReview:
    def __init__(self, code_diff):
        self.code_diff = code_diff
        self.issues = []
    
    def check_hardcoded_secrets(self):
        """Detect hardcoded credentials"""
        patterns = [
            r'password\s*=\s*["\'].*["\']',
            r'api_key\s*=\s*["\'].*["\']',
            r'secret\s*=\s*["\'].*["\']',
            r'token\s*=\s*["\'].*["\']'
        ]
        
        for pattern in patterns:
            if re.search(pattern, self.code_diff, re.IGNORECASE):
                self.issues.append({
                    'type': 'hardcoded_secret',
                    'severity': 'critical',
                    'message': 'Potential hardcoded credential detected'
                })
    
    def check_sql_injection(self):
        """Detect potential SQL injection"""
        if re.search(r'execute\([^?].*\+.*\)', self.code_diff):
            self.issues.append({
                'type': 'sql_injection',
                'severity': 'high',
                'message': 'Potential SQL injection - use parameterized queries'
            })
    
    def check_xss(self):
        """Detect potential XSS"""
        if 'innerHTML' in self.code_diff or 'dangerouslySetInnerHTML' in self.code_diff:
            self.issues.append({
                'type': 'xss',
                'severity': 'high',
                'message': 'Potential XSS - sanitize user input'
            })

# STRIDE threat model
threat_model = {
    'application': 'Payment API',
    'threats': [
        {
            'category': 'Spoofing',
            'threat': 'Attacker impersonates legitimate user',
            'mitigation': 'Implement OAuth 2.0 + JWT',
            'status': 'implemented'
        },
        {
            'category': 'Tampering',
            'threat': 'Transaction amount modified in transit',
            'mitigation': 'Use HTTPS + request signing',
            'status': 'implemented'
        },
        {
            'category': 'Repudiation',
            'threat': 'User denies making transaction',
            'mitigation': 'Comprehensive audit logging',
            'status': 'planned'
        },
        {
            'category': 'Information Disclosure',
            'threat': 'Sensitive data exposed in logs',
            'mitigation': 'Sanitize logs, encrypt PII',
            'status': 'in_progress'
        },
        {
            'category': 'Denial of Service',
            'threat': 'API overwhelmed with requests',
            'mitigation': 'Rate limiting + WAF',
            'status': 'implemented'
        },
        {
            'category': 'Elevation of Privilege',
            'threat': 'User accesses admin functions',
            'mitigation': 'RBAC + authorization checks',
            'status': 'implemented'
        }
    ]
}

# Automated incident response script
import subprocess
import datetime

def isolate_host(ip_address):
    """Isolate compromised host"""
    # Block at firewall
    subprocess.run([
        'iptables', '-A', 'INPUT', '-s', ip_address, '-j', 'DROP'
    ])
    
    # Disable network interface on host
    subprocess.run([
        'ssh', f'admin@{ip_address}',
        'sudo', 'ifconfig', 'eth0', 'down'
    ])
    
    # Log action
    log_incident_action(
        action='host_isolation',
        target=ip_address,
        timestamp=datetime.datetime.now()
    )

def collect_forensics(ip_address):
    """Collect forensic data"""
    commands = [
        'netstat -an',  # Network connections
        'ps aux',       # Running processes
        'last -a',      # Login history
        'find / -mtime -1',  # Recently modified files
    ]
    
    for cmd in commands:
        output = subprocess.run(
            ['ssh', f'admin@{ip_address}', cmd],
            capture_output=True
        )
        save_evidence(cmd, output.stdout)

# Continuous authentication
def verify_access(user, resource, context):
    # Multi-factor authentication
    if not verify_mfa(user):
        return False
    
    # Device posture check
    if not is_device_compliant(context['device_id']):
        return False
    
    # Location verification
    if context['ip'] not in ALLOWED_LOCATIONS:
        return False
    
    # Risk score
    risk_score = calculate_risk(user, context)
    if risk_score > THRESHOLD:
        require_step_up_auth()
    
    # Just-in-time access
    grant_temporary_access(user, resource, duration='1h')
    
    return True

# Network policy (Kubernetes)
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: api-policy
spec:
  podSelector:
    matchLabels:
      app: api
  policyTypes:
  - Ingress
  - Egress
  ingress:
  - from:
    - podSelector:
        matchLabels:
          app: frontend
    ports:
    - protocol: TCP
      port: 8080
  egress:
  - to:
    - podSelector:
        matchLabels:
          app: database
    ports:
    - protocol: TCP
      port: 5432

# Compliance assessment tool
def assess_compliance(framework='NIST'):
    controls = load_framework_controls(framework)
    results = []
    
    for control in controls:
        status = check_control_implementation(control)
        results.append({
            'control_id': control.id,
            'description': control.description,
            'status': status,  # Implemented, Partial, Not Implemented
            'evidence': collect_evidence(control),
            'remediation': get_remediation_plan(control) if status != 'Implemented' else None
        })
    
    return generate_compliance_report(results)

# Threat intelligence automation
import requests

def check_ioc(indicator, ioc_type='ip'):
    """Check Indicator of Compromise"""
    # Query threat intelligence platform
    response = requests.get(
        f'https://api.threatintel.com/v1/indicators/{ioc_type}/{indicator}',
        headers={'Authorization': f'Bearer {API_KEY}'}
    )
    
    if response.json()['malicious']:
        # Block at firewall
        block_indicator(indicator, ioc_type)
        
        # Alert SOC
        create_alert(
            severity='high',
            title=f'Malicious {ioc_type} detected',
            description=f'{indicator} identified as malicious',
            ioc=indicator,
            threat_actor=response.json()['threat_actor']
        )
        
        # Hunt for related activity
        hunt_for_ioc(indicator)

def enrich_alert(alert):
    """Enrich security alert with threat intelligence"""
    context = {
        'ip_reputation': get_ip_reputation(alert.source_ip),
        'domain_age': get_domain_age(alert.domain),
        'ssl_cert': analyze_ssl_cert(alert.domain),
        'similar_incidents': find_similar_incidents(alert)
    }
    
    alert.context = context
    alert.risk_score = calculate_risk_score(context)
    return alert

# Hunt based on ATT&CK techniques
class ThreatHunt:
    def __init__(self, siem_client):
        self.siem = siem_client
        self.findings = []
    
    def hunt_t1003_credential_dumping(self):
        """Hunt for credential dumping (T1003)"""
        query = '''
        EventID:4688 AND 
        (ProcessName:*lsass.exe* OR 
         ProcessName:*procdump* OR 
         ProcessName:*mimikatz*)
        '''
        
        results = self.siem.search(query, timeframe='24h')
        
        for event in results:
            self.findings.append({
                'technique': 'T1003 - Credential Dumping',
                'host': event['hostname'],
                'process': event['process_name'],
                'user': event['username'],
                'timestamp': event['timestamp'],
                'severity': 'critical'
            })
    
    def hunt_t1078_valid_accounts(self):
        """Hunt for suspicious account usage (T1078)"""
        query = '''
        EventID:4624 AND 
        LogonType:3 AND
        SourceIP:* NOT (SourceIP:10.* OR SourceIP:192.168.*)
        '''
        
        # Look for unusual login patterns
        results = self.siem.search(query, timeframe='7d')
        
        # Detect anomalies
        user_logins = {}
        for event in results:
            user = event['username']
            if user not in user_logins:
                user_logins[user] = []
            user_logins[user].append(event)
        
        # Flag users with logins from multiple countries
        for user, logins in user_logins.items():
            countries = set([l['source_country'] for l in logins])
            if len(countries) > 2:
                self.findings.append({
                    'technique': 'T1078 - Valid Accounts',
                    'user': user,
                    'countries': list(countries),
                    'severity': 'high'
                })
    
    def hunt_t1059_command_execution(self):
        """Hunt for suspicious command execution (T1059)"""
        suspicious_commands = [
            'powershell -enc',
            'powershell -e ',
            'cmd /c echo',
            'wscript',
            'cscript'
        ]
        
        for cmd in suspicious_commands:
            query = f'EventID:4688 AND CommandLine:*{cmd}*'
            results = self.siem.search(query, timeframe='24h')
            
            for event in results:
                self.findings.append({
                    'technique': 'T1059 - Command Execution',
                    'host': event['hostname'],
                    'command': event['command_line'],
                    'user': event['username'],
                    'severity': 'high'
                })

-- Splunk query for lateral movement
index=windows EventCode=4624 LogonType=3
| stats dc(ComputerName) as unique_hosts by Account_Name
| where unique_hosts > 10
| sort - unique_hosts

-- Large outbound transfers
index=firewall action=allowed
| stats sum(bytes_out) as total_bytes by src_ip, dest_ip
| where total_bytes > 1000000000
| sort - total_bytes

-- Registry Run keys
index=windows EventCode=13 
TargetObject="*\\CurrentVersion\\Run*"
| table _time, ComputerName, User, TargetObject, Details

# Automated hunting schedule
import schedule
import time

def run_daily_hunts():
    hunter = ThreatHunt(siem_client)
    
    # Run all hunt queries
    hunter.hunt_t1003_credential_dumping()
    hunter.hunt_t1078_valid_accounts()
    hunter.hunt_t1059_command_execution()
    
    # Generate report
    if hunter.findings:
        report = generate_hunt_report(hunter.findings)
        send_to_slack(report)
        create_tickets(hunter.findings)

# Schedule daily at 2 AM
schedule.every().day.at("02:00").do(run_daily_hunts)

while True:
    schedule.run_pending()
    time.sleep(60)

# Threat Hunt Report

**Date:** 2024-01-15
**Hunter:** Security Team
**Hypothesis:** Credential dumping activity

## Findings
- 3 instances of LSASS memory access detected
- All from same compromised host: WS-1234
- User: contractor_account

## Actions Taken
1. Isolated affected host
2. Reset credentials for contractor_account
3. Collected forensic image
4. Created detection rule for future incidents

## Lessons Learned
- Need better monitoring of contractor accounts
- Implement JIT access for privileged operations

# Security orchestration playbook
def handle_phishing_alert(alert):
    """Automated phishing response"""
    # Extract indicators
    email_data = parse_email(alert.email_id)
    sender = email_data['from']
    links = extract_links(email_data['body'])
    attachments = email_data['attachments']
    
    # Analyze threats
    for link in links:
        if is_malicious_url(link):
            block_url(link)
    
    for attachment in attachments:
        if is_malicious_file(attachment):
            quarantine_file(attachment)
    
    # Block sender
    if sender_reputation(sender) < THRESHOLD:
        block_sender(sender)
    
    # Search for similar emails
    similar_emails = search_emails(
        sender=sender,
        timeframe='24h'
    )
    
    # Delete from all mailboxes
    for email in similar_emails:
        delete_email(email.id)
        notify_recipient(email.recipient)
    
    # Update threat intelligence
    add_to_blocklist(sender, links)
    
    # Create ticket
    create_incident_ticket(
        title=f'Phishing campaign from {sender}',
        affected_users=len(similar_emails)
    )