# Threat Modeling

## Overview

Threat modeling is a structured approach to identifying, quantifying, and addressing security risks in software systems. It helps developers understand security requirements and design secure systems from the start.

## Threat Modeling Process

### 1. Identify Assets
What are you trying to protect?
- User data (PII, credentials, financial information)
- System resources (servers, databases, APIs)
- Intellectual property
- Business reputation
- Availability of services

### 2. Create Architecture Overview
Document the system architecture:
- Data flow diagrams
- System boundaries
- Trust boundaries
- External dependencies
- Entry and exit points

### 3. Identify Threats
Use threat modeling frameworks:
- **STRIDE** (Spoofing, Tampering, Repudiation, Information Disclosure, Denial of Service, Elevation of Privilege)
- **DREAD** (Damage, Reproducibility, Exploitability, Affected Users, Discoverability)
- **Attack Trees**
- **Threat Libraries** (OWASP, MITRE ATT&CK)

### 4. Mitigate Threats
For each identified threat:
- Determine risk level
- Design countermeasures
- Implement security controls
- Verify effectiveness

### 5. Validate and Review
- Review threat model regularly
- Update as system evolves
- Validate mitigations are working
- Document decisions

## STRIDE Framework

### Spoofing
**Definition**: Impersonating someone or something else

**Examples**:
- Fake login pages
- Email spoofing
- IP address spoofing
- Session hijacking

**Mitigations**:
- Strong authentication (MFA)
- Certificate pinning
- Session management
- Cryptographic signatures

### Tampering
**Definition**: Modifying data or code

**Examples**:
- SQL injection
- File modification
- Configuration changes
- Code injection

**Mitigations**:
- Input validation
- Output encoding
- Cryptographic hashing
- Access controls
- Code signing

### Repudiation
**Definition**: Denying that an action occurred

**Examples**:
- Claiming a transaction didn't happen
- Denying sending a message
- Disputing access to resources

**Mitigations**:
- Comprehensive logging
- Digital signatures
- Audit trails
- Non-repudiation mechanisms

### Information Disclosure
**Definition**: Exposing information to unauthorized parties

**Examples**:
- SQL injection exposing data
- Error messages revealing details
- Insecure storage
- Insecure transmission

**Mitigations**:
- Encryption (at rest and in transit)
- Access controls
- Secure error handling
- Data classification
- Least privilege

### Denial of Service (DoS)
**Definition**: Making a service unavailable

**Examples**:
- Resource exhaustion
- Network flooding
- Application crashes
- Slowloris attacks

**Mitigations**:
- Rate limiting
- Resource quotas
- Input validation
- Load balancing
- DDoS protection services

### Elevation of Privilege
**Definition**: Gaining unauthorized access or privileges

**Examples**:
- Privilege escalation bugs
- Bypassing access controls
- Exploiting vulnerabilities
- Social engineering

**Mitigations**:
- Principle of least privilege
- Access control enforcement
- Input validation
- Secure defaults
- Regular security updates

## Threat Modeling Tools

### Microsoft Threat Modeling Tool
- Free tool for creating threat models
- STRIDE-based analysis
- Visual diagramming
- Threat generation

### OWASP Threat Dragon
- Open-source threat modeling tool
- Web-based interface
- Supports multiple methodologies
- Integration with development workflows

### Attack Trees
- Visual representation of attack paths
- Shows how threats can be realized
- Helps identify mitigation points
- Useful for complex systems

## Common Threat Scenarios

### Web Application Threats
- **SQL Injection**: Unvalidated input in database queries
- **XSS (Cross-Site Scripting)**: Injecting malicious scripts
- **CSRF (Cross-Site Request Forgery)**: Forcing authenticated actions
- **Session Fixation**: Attacker sets session ID
- **Path Traversal**: Accessing files outside web root

### API Threats
- **Broken Authentication**: Weak or missing authentication
- **Excessive Data Exposure**: Returning too much data
- **Lack of Rate Limiting**: Allowing abuse
- **Mass Assignment**: Modifying unintended fields
- **Insecure Direct Object References**: Accessing unauthorized resources

### Cloud Threats
- **Misconfigured Storage**: Public S3 buckets, etc.
- **Insecure APIs**: Weak authentication/authorization
- **Data Breaches**: Insufficient encryption
- **Account Hijacking**: Weak credentials
- **Insider Threats**: Excessive permissions

## Threat Modeling Best Practices

### Start Early
- Begin threat modeling during design phase
- Update as system evolves
- Include in security review process

### Be Comprehensive
- Consider all entry points
- Think about all data flows
- Consider all user roles
- Don't forget internal threats

### Document Everything
- Document identified threats
- Document mitigations
- Document assumptions
- Keep threat models up to date

### Involve the Team
- Include developers, architects, security
- Use collaborative tools
- Regular review sessions
- Share knowledge

### Use Frameworks
- Don't reinvent the wheel
- Use established methodologies (STRIDE, DREAD)
- Leverage threat libraries
- Learn from industry examples

## References

- [OWASP Threat Modeling](https://owasp.org/www-community/Threat_Modeling)
- [Microsoft Threat Modeling](https://docs.microsoft.com/en-us/azure/security/develop/threat-modeling-tool)
- [MITRE ATT&CK](https://attack.mitre.org/)
- [STRIDE Methodology](https://en.wikipedia.org/wiki/STRIDE_(security))

