Senior Security Engineer

Security engineering tools for threat modeling, vulnerability analysis, secure architecture design, and penetration testing.

Table of Contents

• Threat Modeling Workflow
• Security Architecture Workflow
• Vulnerability Assessment Workflow
• Secure Code Review Workflow
• Incident Response Workflow
• Security Tools Reference
• Tools and References

Threat Modeling Workflow

Identify and analyze security threats using STRIDE methodology.

Workflow: Conduct Threat Model

1. Define system scope and boundaries:
   • Identify assets to protect
   • Map trust boundaries
   • Document data flows
2. Create data flow diagram:
   • External entities (users, services)
   • Processes (application components)
   • Data stores (databases, caches)
   • Data flows (APIs, network connections)
3. Apply STRIDE to each DFD element (see STRIDE per Element Matrix below)
4. Score risks using DREAD:
   • Damage potential (1-10)
   • Reproducibility (1-10)
   • Exploitability (1-10)
   • Affected users (1-10)
   • Discoverability (1-10)
5. Prioritize threats by risk score
6. Define mitigations for each threat
7. Document in threat model report
8. Validation: All DFD elements analyzed; STRIDE applied; threats scored; mitigations mapped

STRIDE Threat Categories

STRIDE per Element Matrix

See: references/threat-modeling-guide.md

Security Architecture Workflow

Design secure systems using defense-in-depth principles.

Workflow: Design Secure Architecture

1. Define security requirements:
   • Compliance requirements (GDPR, HIPAA, PCI-DSS)
   • Data classification (public, internal, confidential, restricted)
   • Threat model inputs
2. Apply defense-in-depth layers:
   • Perimeter: WAF, DDoS protection, rate limiting
   • Network: Segmentation, IDS/IPS, mTLS
   • Host: Patching, EDR, hardening
   • Application: Input validation, authentication, secure coding
   • Data: Encryption at rest and in transit
3. Implement Zero Trust principles:
   • Verify explicitly (every request)
   • Least privilege access (JIT/JEA)
   • Assume breach (segment, monitor)
4. Configure authentication and authorization:
   • Identity provider selection
   • MFA requirements
   • RBAC/ABAC model
5. Design encryption strategy:
   • Key management approach
   • Algorithm selection
   • Certificate lifecycle
6. Plan security monitoring:
   • Log aggregation
   • SIEM integration
   • Alerting rules
7. Document architecture decisions
8. Validation: Defense-in-depth layers defined; Zero Trust applied; encryption strategy documented; monitoring planned

Defense-in-Depth Layers

Layer 1: PERIMETER
  WAF, DDoS mitigation, DNS filtering, rate limiting

Layer 2: NETWORK
  Segmentation, IDS/IPS, network monitoring, VPN, mTLS

Layer 3: HOST
  Endpoint protection, OS hardening, patching, logging

Layer 4: APPLICATION
  Input validation, authentication, secure coding, SAST

Layer 5: DATA
  Encryption at rest/transit, access controls, DLP, backup

Authentication Pattern Selection

See: references/security-architecture-patterns.md

Vulnerability Assessment Workflow

Identify and remediate security vulnerabilities in applications.

Workflow: Conduct Vulnerability Assessment

1. Define assessment scope:
   • In-scope systems and applications
   • Testing methodology (black box, gray box, white box)
   • Rules of engagement
2. Gather information:
   • Technology stack inventory
   • Architecture documentation
   • Previous vulnerability reports
3. Perform automated scanning:
   • SAST (static analysis)
   • DAST (dynamic analysis)
   • Dependency scanning
   • Secret detection
4. Conduct manual testing:
   • Business logic flaws
   • Authentication bypass
   • Authorization issues
   • Injection vulnerabilities
5. Classify findings by severity:
   • Critical: Immediate exploitation risk
   • High: Significant impact, easier to exploit
   • Medium: Moderate impact or difficulty
   • Low: Minor impact
6. Develop remediation plan:
   • Prioritize by risk
   • Assign owners
   • Set deadlines
7. Verify fixes and document
8. Validation: Scope defined; automated and manual testing complete; findings classified; remediation tracked

For OWASP Top 10 vulnerability descriptions and testing guidance, refer to owasp.org/Top10.

Vulnerability Severity Matrix

Secure Code Review Workflow

Review code for security vulnerabilities before deployment.

Workflow: Conduct Security Code Review

1. Establish review scope:
   • Changed files and functions
   • Security-sensitive areas (auth, crypto, input handling)
   • Third-party integrations
2. Run automated analysis:
   • SAST tools (Semgrep, CodeQL, Bandit)
   • Secret scanning
   • Dependency vulnerability check
3. Review authentication code:
   • Password handling (hashing, storage)
   • Session management
   • Token validation
4. Review authorization code:
   • Access control checks
   • RBAC implementation
   • Privilege boundaries
5. Review data handling:
   • Input validation
   • Output encoding
   • SQL query construction
   • File path handling
6. Review cryptographic code:
   • Algorithm selection
   • Key management
   • Random number generation
7. Document findings with severity
8. Validation: Automated scans passed; auth/authz reviewed; data handling checked; crypto verified; findings documented

Security Code Review Checklist

Secure vs Insecure Patterns

Inline Code Examples

SQL Injection — insecure vs. secure (Python):

# ❌ Insecure: string formatting allows SQL injection
query = f"SELECT * FROM users WHERE username = '{username}'"
cursor.execute(query)

# ✅ Secure: parameterized query — user input never interpreted as SQL
query = "SELECT * FROM users WHERE username = %s"
cursor.execute(query, (username,))

Password Hashing with Argon2id (Python):

from argon2 import PasswordHasher

ph = PasswordHasher()          # uses secure defaults (time_cost, memory_cost)

# On registration
hashed = ph.hash(plain_password)

# On login — raises argon2.exceptions.VerifyMismatchError on failure
ph.verify(hashed, plain_password)

Secret Scanning — core pattern matching (Python):

import re, pathlib

SECRET_PATTERNS = {
    "aws_access_key":  re.compile(r"AKIA[0-9A-Z]{16}"),
    "github_token":    re.compile(r"ghp_[A-Za-z0-9]{36}"),
    "private_key":     re.compile(r"-----BEGIN (RSA |EC )?PRIVATE KEY-----"),
    "generic_secret":  re.compile(r'(?i)(password|secret|api_key)\s*=\s*["\']?\S{8,}'),
}

def scan_file(path: pathlib.Path) -> list[dict]:
    findings = []
    for lineno, line in enumerate(path.read_text(errors="replace").splitlines(), 1):
        for name, pattern in SECRET_PATTERNS.items():
            if pattern.search(line):
                findings.append({"file": str(path), "line": lineno, "type": name})
    return findings

Incident Response Workflow

Respond to and contain security incidents.

Workflow: Handle Security Incident

1. Identify and triage:
   • Validate incident is genuine
   • Assess initial scope and severity
   • Activate incident response team
2. Contain the threat:
   • Isolate affected systems
   • Block malicious IPs/accounts
   • Disable compromised credentials
3. Eradicate root cause:
   • Remove malware/backdoors
   • Patch vulnerabilities
   • Update configurations
4. Recover operations:
   • Restore from clean backups
   • Verify system integrity
   • Monitor for recurrence
5. Conduct post-mortem:
   • Timeline reconstruction
   • Root cause analysis
   • Lessons learned
6. Implement improvements:
   • Update detection rules
   • Enhance controls
   • Update runbooks
7. Document and report
8. Validation: Threat contained; root cause eliminated; systems recovered; post-mortem complete; improvements implemented

Incident Severity Levels

Incident Response Checklist

Security Tools Reference

Recommended Security Tools

Cryptographic Algorithm Selection

See: references/cryptography-implementation.md

Tools and References

Scripts

For usage, see the inline code examples in Secure Code Review Workflow and the script source files directly.

References

Security Standards Reference

Security Headers Checklist

For compliance framework requirements (OWASP ASVS, CIS Benchmarks, NIST CSF, PCI-DSS, HIPAA, SOC 2), refer to the respective official documentation.

Related Skills