File: THREAT_MODEL — Documentation by YARD 0.9.45

# Threat Model Outline for oauth2 Ruby Gem

## 1. Overview

This document outlines the threat model for the `oauth2` Ruby gem, which implements OAuth 2.0, 2.1, and OIDC Core protocols. The gem is used to facilitate secure authorization and authentication in Ruby applications.

## 2. Assets to Protect

- OAuth access tokens, refresh tokens, and ID tokens
- User credentials (if handled)
- Client secrets and application credentials
- Sensitive user data accessed via OAuth
- Private keys and certificates (for signing/verifying tokens)

## 3. Potential Threat Actors

- External attackers (internet-based)
- Malicious OAuth clients or resource servers
- Insiders (developers, maintainers)
- Compromised dependencies

## 4. Attack Surfaces

- OAuth endpoints (authorization, token, revocation, introspection)
- HTTP request/response handling
- Token storage and management
- Configuration files and environment variables
- Dependency supply chain

## 5. Threats and Mitigations

### 5.1 Token Leakage

- Threat: Tokens exposed via logs, URLs, or insecure storage
- Mitigations:
  - Avoid logging sensitive tokens
  - Use secure storage mechanisms
  - Never expose tokens in URLs

### 5.2 Token Replay and Forgery

- Threat: Attackers reuse or forge tokens
- Mitigations:
  - Validate token signatures and claims
  - Use short-lived tokens and refresh tokens
  - Implement token revocation

### 5.3 Insecure Communication

- Threat: Data intercepted via MITM attacks
- Mitigations:
  - Enforce HTTPS for all communications
  - Validate SSL/TLS certificates

### 5.4 Client Secret Exposure

- Threat: Client secrets leaked in code or version control
- Mitigations:
  - Store secrets in environment variables or secure vaults
  - Never commit secrets to source control

### 5.5 Dependency Vulnerabilities

- Threat: Vulnerabilities in third-party libraries
- Mitigations:
  - Regularly update dependencies
  - Use tools like `bundler-audit` for vulnerability scanning

### 5.6 Improper Input Validation

- Threat: Injection attacks via untrusted input
- Mitigations:
  - Validate and sanitize all inputs
  - Use parameterized queries and safe APIs

### 5.7 Request-Target Trust Boundary Expansion

- Threat: Applications may pass untrusted or insufficiently validated absolute URLs into request paths that can carry OAuth credentials or authenticated state.
- Risk: This can expand trust boundaries, contributing to token leakage, authenticated requests to unintended hosts, or SSRF-like pivoting in the surrounding application.
- Mitigations:
  - Prefer relative paths where practical
  - Do not pass untrusted absolute URLs into token-bearing clients
  - Validate or allowlist outbound request targets at the application layer
  - Treat request-target validation as a separate concern from log redaction and token storage

### 5.8 Insufficient Logging and Monitoring

- Threat: Attacks go undetected
- Mitigations:
  - Log security-relevant events (without sensitive data)
  - Monitor for suspicious activity

## 6. Assumptions

- The gem is used in a secure environment with up-to-date Ruby and dependencies
- End-users are responsible for secure configuration and deployment

## 7. Out of Scope

- Security of external OAuth providers
- Application-level business logic

## 8. References

- OAuth 2.0 Threat Model and Security Considerations (RFC 6819)
- OWASP Top Ten

This outline should be reviewed and updated regularly as the project evolves.