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

• Define system scope and boundaries:

• Identify assets to protect

• Map trust boundaries

• Document data flows

• Create data flow diagram:

• External entities (users, services)

• Processes (application components)

• Data stores (databases, caches)

• Data flows (APIs, network connections)

• Apply STRIDE to each DFD element (see STRIDE per Element Matrix below)

• Score risks using DREAD:

• Damage potential (1-10)

• Reproducibility (1-10)

• Exploitability (1-10)

• Affected users (1-10)

• Discoverability (1-10)

• Prioritize threats by risk score

• Define mitigations for each threat

• Document in threat model report

• Validation: All DFD elements analyzed; STRIDE applied; threats scored; mitigations mapped

STRIDE Threat Categories

Category Security Property Mitigation Focus

Spoofing Authentication MFA, certificates, strong auth

Tampering Integrity Signing, checksums, validation

Repudiation Non-repudiation Audit logs, digital signatures

Information Disclosure Confidentiality Encryption, access controls

Denial of Service Availability Rate limiting, redundancy

Elevation of Privilege Authorization RBAC, least privilege

STRIDE per Element Matrix

DFD Element S T R I D E

External Entity X

X

Process X X X X X X

Data Store

X X X X

Data Flow

X

X X

See: references/threat-modeling-guide.md

Security Architecture Workflow

Design secure systems using defense-in-depth principles.

Workflow: Design Secure Architecture

• Define security requirements:

• Compliance requirements (GDPR, HIPAA, PCI-DSS)

• Data classification (public, internal, confidential, restricted)

• Threat model inputs

• 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

• Implement Zero Trust principles:

• Verify explicitly (every request)

• Least privilege access (JIT/JEA)

• Assume breach (segment, monitor)

• Configure authentication and authorization:

• Identity provider selection

• MFA requirements

• RBAC/ABAC model

• Design encryption strategy:

• Key management approach

• Algorithm selection

• Certificate lifecycle

• Plan security monitoring:

• Log aggregation

• SIEM integration

• Alerting rules

• Document architecture decisions

• 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

Use Case Recommended Pattern

Web application OAuth 2.0 + PKCE with OIDC

API authentication JWT with short expiration + refresh tokens

Service-to-service mTLS with certificate rotation

CLI/Automation API keys with IP allowlisting

High security FIDO2/WebAuthn hardware keys

See: references/security-architecture-patterns.md

Vulnerability Assessment Workflow

Identify and remediate security vulnerabilities in applications.

Workflow: Conduct Vulnerability Assessment

• Define assessment scope:

• In-scope systems and applications

• Testing methodology (black box, gray box, white box)

• Rules of engagement

• Gather information:

• Technology stack inventory

• Architecture documentation

• Previous vulnerability reports

• Perform automated scanning:

• SAST (static analysis)

• DAST (dynamic analysis)

• Dependency scanning

• Secret detection

• Conduct manual testing:

• Business logic flaws

• Authentication bypass

• Authorization issues

• Injection vulnerabilities

• Classify findings by severity:

• Critical: Immediate exploitation risk

• High: Significant impact, easier to exploit

• Medium: Moderate impact or difficulty

• Low: Minor impact

• Develop remediation plan:

• Prioritize by risk

• Assign owners

• Set deadlines

• Verify fixes and document

• 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

Impact \ Exploitability Easy Moderate Difficult

Critical Critical Critical High

High Critical High Medium

Medium High Medium Low

Low Medium Low Low

Secure Code Review Workflow

Review code for security vulnerabilities before deployment.

Workflow: Conduct Security Code Review

• Establish review scope:

• Changed files and functions

• Security-sensitive areas (auth, crypto, input handling)

• Third-party integrations

• Run automated analysis:

• SAST tools (Semgrep, CodeQL, Bandit)

• Secret scanning

• Dependency vulnerability check

• Review authentication code:

• Password handling (hashing, storage)

• Session management

• Token validation

• Review authorization code:

• Access control checks

• RBAC implementation

• Privilege boundaries

• Review data handling:

• Input validation

• Output encoding

• SQL query construction

• File path handling

• Review cryptographic code:

• Algorithm selection

• Key management

• Random number generation

• Document findings with severity

• Validation: Automated scans passed; auth/authz reviewed; data handling checked; crypto verified; findings documented

Security Code Review Checklist

Category Check Risk

Input Validation All user input validated and sanitized Injection

Output Encoding Context-appropriate encoding applied XSS

Authentication Passwords hashed with Argon2/bcrypt Credential theft

Session Secure cookie flags set (HttpOnly, Secure, SameSite) Session hijacking

Authorization Server-side permission checks on all endpoints Privilege escalation

SQL Parameterized queries used exclusively SQL injection

File Access Path traversal sequences rejected Path traversal

Secrets No hardcoded credentials or keys Information disclosure

Dependencies Known vulnerable packages updated Supply chain

Logging Sensitive data not logged Information disclosure

Secure vs Insecure Patterns

Pattern Issue Secure Alternative

SQL string formatting SQL injection Use parameterized queries with placeholders

Shell command building Command injection Use subprocess with argument lists, no shell

Path concatenation Path traversal Validate and canonicalize paths

MD5/SHA1 for passwords Weak hashing Use Argon2id or bcrypt

Math.random for tokens Predictable values Use crypto.getRandomValues

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

• Identify and triage:

• Validate incident is genuine

• Assess initial scope and severity

• Activate incident response team

• Contain the threat:

• Isolate affected systems

• Block malicious IPs/accounts

• Disable compromised credentials

• Eradicate root cause:

• Remove malware/backdoors

• Patch vulnerabilities

• Update configurations

• Recover operations:

• Restore from clean backups

• Verify system integrity

• Monitor for recurrence

• Conduct post-mortem:

• Timeline reconstruction

• Root cause analysis

• Lessons learned

• Implement improvements:

• Update detection rules

• Enhance controls

• Update runbooks

• Document and report

• Validation: Threat contained; root cause eliminated; systems recovered; post-mortem complete; improvements implemented

Incident Severity Levels

Level Response Time Escalation

P1 - Critical (active breach/exfiltration) Immediate CISO, Legal, Executive

P2 - High (confirmed, contained) 1 hour Security Lead, IT Director

P3 - Medium (potential, under investigation) 4 hours Security Team

P4 - Low (suspicious, low impact) 24 hours On-call engineer

Incident Response Checklist

Phase Actions

Identification Validate alert, assess scope, determine severity

Containment Isolate systems, preserve evidence, block access

Eradication Remove threat, patch vulnerabilities, reset credentials

Recovery Restore services, verify integrity, increase monitoring

Lessons Learned Document timeline, identify gaps, update procedures

Security Tools Reference

Recommended Security Tools

Category Tools

SAST Semgrep, CodeQL, Bandit (Python), ESLint security plugins

DAST OWASP ZAP, Burp Suite, Nikto

Dependency Scanning Snyk, Dependabot, npm audit, pip-audit

Secret Detection GitLeaks, TruffleHog, detect-secrets

Container Security Trivy, Clair, Anchore

Infrastructure Checkov, tfsec, ScoutSuite

Network Wireshark, Nmap, Masscan

Penetration Metasploit, sqlmap, Burp Suite Pro

Cryptographic Algorithm Selection

Use Case Algorithm Key Size

Symmetric encryption AES-256-GCM 256 bits

Password hashing Argon2id N/A (use defaults)

Message authentication HMAC-SHA256 256 bits

Digital signatures Ed25519 256 bits

Key exchange X25519 256 bits

TLS TLS 1.3 N/A

See: references/cryptography-implementation.md

Tools and References

Scripts

Script Purpose

threat_modeler.py STRIDE threat analysis with DREAD risk scoring; JSON and text output; interactive guided mode

secret_scanner.py Detect hardcoded secrets and credentials across 20+ patterns; CI/CD integration ready

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

References

Document Content

security-architecture-patterns.md Zero Trust, defense-in-depth, authentication patterns, API security

threat-modeling-guide.md STRIDE methodology, attack trees, DREAD scoring, DFD creation

cryptography-implementation.md AES-GCM, RSA, Ed25519, password hashing, key management

Security Standards Reference

Security Headers Checklist

Header Recommended Value

Content-Security-Policy default-src self; script-src self

X-Frame-Options DENY

X-Content-Type-Options nosniff

Strict-Transport-Security max-age=31536000; includeSubDomains

Referrer-Policy strict-origin-when-cross-origin

Permissions-Policy geolocation=(), microphone=(), camera=()

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

Related Skills

Skill Integration Point

senior-devops CI/CD security, infrastructure hardening

senior-secops Security monitoring, incident response

senior-backend Secure API development

senior-architect Security architecture decisions