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BUSINESS POSTURE

  • Business priorities and goals:
    • Provide a lightweight and flexible web framework for Python developers.
    • Enable rapid development of web applications and APIs.
    • Maintain a simple and extensible core with a focus on microframework principles.
    • Foster a vibrant and active community around the framework.
  • Most important business risks:
    • Security vulnerabilities in the framework could impact a large number of applications built with Flask.
    • Lack of maintenance or slow security updates could lead to widespread security issues.
    • Breaking changes in the framework could disrupt existing applications and developer workflows.
    • Poor documentation or lack of community support could hinder adoption and developer productivity.

SECURITY POSTURE

  • Existing security controls:

    • security control: Code review process on GitHub for contributions (described in GitHub repository contribution guidelines).
    • security control: Security advisories and vulnerability reporting process (described in Flask documentation and security policy).
    • security control: Regular releases with bug fixes and security patches (visible in GitHub releases and changelog).
    • security control: Usage of Werkzeug, a robust WSGI library, for handling HTTP requests and responses (implicit in Flask architecture).
    • accepted risk: Reliance on developers to implement security best practices in their applications built with Flask.
    • accepted risk: Vulnerabilities in dependencies used by Flask or applications built with Flask.

  • Recommended security controls:

    • security control: Automated security scanning (SAST/DAST) of Flask codebase in CI/CD pipeline.
    • security control: Dependency vulnerability scanning and management for Flask and its dependencies.
    • security control: Security focused documentation and examples for developers using Flask.
    • security control: Penetration testing or security audits of Flask framework on a regular basis.

  • Security requirements:

    • Authentication:
      • Applications built with Flask should be able to implement various authentication mechanisms (e.g., session-based, token-based, OAuth).
      • Flask itself should not enforce any specific authentication method, providing flexibility to developers.
    • Authorization:
      • Applications built with Flask should be able to implement fine-grained authorization controls to manage access to resources.
      • Flask should provide tools and patterns to facilitate authorization implementation.
    • Input validation:
      • Applications built with Flask must validate all user inputs to prevent injection attacks (e.g., SQL injection, XSS).
      • Flask should provide guidance and mechanisms for input validation (e.g., request parsing, form handling).
    • Cryptography:
      • Applications built with Flask may need to use cryptography for various purposes (e.g., password hashing, data encryption, secure communication).
      • Flask should integrate well with Python cryptography libraries and provide secure defaults where applicable (e.g., session management).

DESIGN

C4 CONTEXT

flowchart LR
    subgraph "Flask Project Context"
        center_node("Flask Framework")
    end

    user_dev("Web Developers")
    python_ecosystem("Python Ecosystem")
    web_servers("Web Servers")
    databases("Databases")
    browsers("Web Browsers")

    user_dev -- "Uses to build web applications" --> center_node
    center_node -- "Leverages libraries from" --> python_ecosystem
    center_node -- "Applications deployed on" --> web_servers
    center_node -- "Applications interact with" --> databases
    web_servers -- "Serves applications to" --> browsers
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  • Elements of context diagram:
      • Name: Flask Framework
      • Type: Software System
      • Description: A microframework for Python based on Werkzeug, Jinja 2 and good intentions. It aims to keep the core simple but extensible.
      • Responsibilities: Provides core functionalities for web application development, including routing, request handling, response generation, and template rendering.
      • Security controls: Code review, security advisories, regular releases, dependency management.
      • Name: Web Developers
      • Type: Person
      • Description: Software engineers who use Flask to build web applications and APIs.
      • Responsibilities: Develop, deploy, and maintain web applications using Flask, implement security best practices in their applications.
      • Security controls: Secure coding practices, input validation, authentication, authorization in applications they build.
      • Name: Python Ecosystem
      • Type: Software System
      • Description: Collection of Python libraries, packages, and tools that Flask and Flask applications rely on (e.g., Werkzeug, Jinja2, cryptography libraries).
      • Responsibilities: Provide reusable components and functionalities for Python development, including web development.
      • Security controls: Dependency vulnerability scanning, secure package management (pip, virtual environments).
      • Name: Web Servers
      • Type: Software System
      • Description: Servers like Nginx, Apache, or WSGI servers (e.g., Gunicorn, uWSGI) that host and serve Flask applications.
      • Responsibilities: Handle HTTP requests, serve static files, manage application processes, and provide a runtime environment for Flask applications.
      • Security controls: Server hardening, TLS/SSL configuration, access control, web application firewall (WAF).
      • Name: Databases
      • Type: Software System
      • Description: Database systems (e.g., PostgreSQL, MySQL, SQLite) used by Flask applications to store and retrieve data.
      • Responsibilities: Persist application data, provide data access and management capabilities.
      • Security controls: Database access control, encryption at rest and in transit, input sanitization to prevent SQL injection.
      • Name: Web Browsers
      • Type: Software System
      • Description: Clients used by end-users to access web applications built with Flask.
      • Responsibilities: Render web pages, execute client-side scripts, interact with web applications.
      • Security controls: Browser security features (e.g., Content Security Policy, Same-Origin Policy), user awareness of phishing and malicious websites.

C4 CONTAINER

flowchart LR
    subgraph "Flask Application Container"
        flask_lib("Flask Library")
        werkzeug_lib("Werkzeug Library")
        jinja2_lib("Jinja2 Library")
        extensions("Flask Extensions")
    end

    web_server("Web Server (e.g., Gunicorn)")
    python_runtime("Python Runtime")

    web_server -- "Hosts" --> python_runtime
    python_runtime -- "Runs" --> flask_lib
    flask_lib -- "Uses" --> werkzeug_lib
    flask_lib -- "Uses" --> jinja2_lib
    flask_lib -- "Extends with" --> extensions

    style flask_lib fill:#f9f,stroke:#333,stroke-width:2px
    style werkzeug_lib fill:#ccf,stroke:#333,stroke-width:2px
    style jinja2_lib fill:#ccf,stroke:#333,stroke-width:2px
    style extensions fill:#ccf,stroke:#333,stroke-width:2px
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  • Elements of container diagram:
      • Name: Flask Library
      • Type: Library
      • Description: The core Flask framework library, providing essential web framework functionalities.
      • Responsibilities: Routing, request and response handling, application context management, extension loading.
      • Security controls: Code review, security testing, input validation within framework components, secure session management.
      • Name: Werkzeug Library
      • Type: Library
      • Description: A comprehensive WSGI web application library that Flask is built upon. Handles low-level details of HTTP and WSGI.
      • Responsibilities: HTTP request parsing, response building, WSGI server integration, cookie handling, security utilities.
      • Security controls: Security audits, input validation, protection against common web attacks (e.g., CSRF, XSS in utilities).
      • Name: Jinja2 Library
      • Type: Library
      • Description: A modern and designer-friendly templating language for Python, used by Flask for rendering dynamic web pages.
      • Responsibilities: Template rendering, template inheritance, escaping output to prevent XSS, template security sandboxing.
      • Security controls: Auto-escaping of variables, template sandboxing (if enabled), security considerations in template design.
      • Name: Flask Extensions
      • Type: Library
      • Description: Community-developed extensions that add functionalities to Flask, such as database integration, authentication, and API frameworks.
      • Responsibilities: Extend Flask's capabilities, provide reusable components for common web development tasks.
      • Security controls: Security depends on individual extensions; developers should choose and review extensions carefully.
      • Name: Web Server (e.g., Gunicorn)
      • Type: Application Server
      • Description: A production-ready WSGI server used to host and serve Flask applications.
      • Responsibilities: Process management, handling concurrent requests, serving static files, integrating with load balancers and reverse proxies.
      • Security controls: Server hardening, process isolation, resource limits, TLS/SSL termination, security configurations.
      • Name: Python Runtime
      • Type: Runtime Environment
      • Description: The Python interpreter and standard library required to run Flask and its applications.
      • Responsibilities: Execute Python code, manage memory, provide core functionalities for Python programs.
      • Security controls: Keeping Python runtime updated with security patches, secure Python installation and configuration.

DEPLOYMENT

Deployment Solution: Containerized Deployment on Cloud Platform (e.g., AWS ECS, Google Kubernetes Engine)

flowchart LR
    subgraph "Cloud Platform (e.g., AWS)"
        subgraph "Container Orchestration (e.g., ECS)"
            load_balancer("Load Balancer")
            container_instance_1("Container Instance 1")
            container_instance_2("Container Instance 2")
            container_registry("Container Registry")
        end
        database_service("Database Service (e.g., RDS)")
        monitoring_service("Monitoring Service (e.g., CloudWatch)")
    end

    developer_pc("Developer PC")

    developer_pc -- "Pushes Docker Image to" --> container_registry
    load_balancer -- "Distributes traffic to" --> container_instance_1
    load_balancer -- "Distributes traffic to" --> container_instance_2
    container_instance_1 -- "Runs Flask Application Container" --> database_service
    container_instance_2 -- "Runs Flask Application Container" --> database_service
    container_instance_1 -- "Sends logs to" --> monitoring_service
    container_instance_2 -- "Sends logs to" --> monitoring_service
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  • Elements of deployment diagram:
      • Name: Developer PC
      • Type: Development Environment
      • Description: Developer's local machine used for writing code, building Docker images, and testing.
      • Responsibilities: Code development, local testing, building and pushing container images.
      • Security controls: Developer workstation security, code repository access control, secure development practices.
      • Name: Container Registry
      • Type: Registry Service
      • Description: Service for storing and managing Docker container images (e.g., Docker Hub, AWS ECR, Google GCR).
      • Responsibilities: Securely store and distribute container images, manage image versions and access control.
      • Security controls: Access control, vulnerability scanning of container images, image signing and verification.
      • Name: Load Balancer
      • Type: Network Load Balancer
      • Description: Distributes incoming traffic across multiple container instances running Flask applications.
      • Responsibilities: Traffic distribution, health checks, SSL termination, high availability.
      • Security controls: TLS/SSL configuration, DDoS protection, access control lists (ACLs), security groups.
      • Name: Container Instance 1 & 2
      • Type: Compute Instance (e.g., EC2, VMs)
      • Description: Virtual machines or compute instances running container runtime (e.g., Docker, containerd) and hosting Flask application containers.
      • Responsibilities: Run Flask application containers, execute application code, handle requests, interact with database and other services.
      • Security controls: Instance hardening, security groups, container isolation, resource limits, runtime security (e.g., AppArmor, SELinux).
      • Name: Database Service (e.g., RDS)
      • Type: Managed Database Service
      • Description: Managed database service provided by cloud platform, used by Flask applications for data persistence.
      • Responsibilities: Data storage, data management, database operations, backups, high availability.
      • Security controls: Database access control, encryption at rest and in transit, database monitoring, vulnerability management.
      • Name: Monitoring Service (e.g., CloudWatch)
      • Type: Monitoring Service
      • Description: Cloud monitoring service used to collect logs, metrics, and monitor the health and performance of Flask applications and infrastructure.
      • Responsibilities: Log aggregation, metrics collection, alerting, performance monitoring, security monitoring.
      • Security controls: Access control to monitoring data, secure log storage, anomaly detection for security events.

BUILD

flowchart LR
    developer("Developer") --> code_commit("Code Commit (GitHub)")
    code_commit --> github_actions("GitHub Actions CI")
    github_actions --> build_stage("Build Stage")
    build_stage --> test_stage("Test Stage")
    test_stage --> security_scan_stage("Security Scan Stage (SAST, Dependency Check)")
    security_scan_stage --> containerize_stage("Containerize Stage (Docker Build)")
    containerize_stage --> container_registry("Container Registry (Push Image)")

    subgraph "Build Stage"
        dependency_install("Dependency Install (pip install)")
        code_compile("Code Compilation (if needed)")
    end
    build_stage --> dependency_install
    build_stage --> code_compile

    subgraph "Test Stage"
        unit_tests("Unit Tests")
        integration_tests("Integration Tests")
    end
    test_stage --> unit_tests
    test_stage --> integration_tests

    subgraph "Security Scan Stage"
        sast_scan("SAST Scan (e.g., Bandit)")
        dependency_check("Dependency Vulnerability Check (e.g., pip-audit)")
    end
    security_scan_stage --> sast_scan
    security_scan_stage --> dependency_check
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  • Elements of build diagram:
      • Name: Developer
      • Type: Person
      • Description: Software developer writing and committing code changes.
      • Responsibilities: Writing code, running local tests, committing code to repository.
      • Security controls: Secure coding practices, code review, workstation security.
      • Name: Code Commit (GitHub)
      • Type: Version Control System
      • Description: GitHub repository hosting Flask project code.
      • Responsibilities: Version control, code collaboration, triggering CI/CD pipelines.
      • Security controls: Access control, branch protection, commit signing, audit logs.
      • Name: GitHub Actions CI
      • Type: CI/CD Platform
      • Description: GitHub's built-in CI/CD service used to automate build, test, and deployment processes.
      • Responsibilities: Automated build, test, security scanning, and containerization of Flask applications.
      • Security controls: Secure workflow definitions, secret management, access control, audit logs.
      • Name: Build Stage
      • Type: CI Stage
      • Description: Stage in CI pipeline responsible for building the application.
      • Responsibilities: Installing dependencies, compiling code (if necessary), preparing build artifacts.
      • Security controls: Dependency vulnerability scanning during install, secure build environment, build artifact integrity checks.
      • Name: Test Stage
      • Type: CI Stage
      • Description: Stage in CI pipeline responsible for running automated tests.
      • Responsibilities: Running unit tests, integration tests, ensuring code quality and functionality.
      • Security controls: Test environment isolation, secure test data management.
      • Name: Security Scan Stage
      • Type: CI Stage
      • Description: Stage in CI pipeline responsible for performing security scans.
      • Responsibilities: Static Application Security Testing (SAST), dependency vulnerability scanning, identifying potential security issues.
      • Security controls: SAST tool configuration, dependency vulnerability database updates, fail-on-high-severity-findings policy.
      • Name: Containerize Stage
      • Type: CI Stage
      • Description: Stage in CI pipeline responsible for building Docker container image.
      • Responsibilities: Building Docker image, tagging image, pushing image to container registry.
      • Security controls: Base image selection, minimal image layers, vulnerability scanning of base images, image signing.
      • Name: Container Registry
      • Type: Registry Service
      • Description: Service for storing and managing Docker container images.
      • Responsibilities: Securely store and distribute container images.
      • Security controls: Access control, vulnerability scanning, image signing.

RISK ASSESSMENT

  • Critical business processes:
    • Development and maintenance of the Flask framework itself.
    • Usage of Flask framework by developers to build and deploy web applications.
    • Community contributions and ecosystem growth around Flask.
  • Data we are trying to protect and their sensitivity:
    • Flask framework source code: High sensitivity - Integrity and availability are crucial to maintain trust and prevent malicious modifications. Confidentiality is less critical as it is open source.
    • Flask framework releases and packages: High sensitivity - Integrity is paramount to ensure users download and use genuine, untampered versions. Availability is also important for continuous usage.
    • Flask documentation and website: Medium sensitivity - Integrity and availability are important to provide accurate and reliable information to users.
    • User data in applications built with Flask: Sensitivity depends on the application. Flask itself does not handle user data, but applications built with it often do. Security of user data is the responsibility of application developers.

QUESTIONS & ASSUMPTIONS

  • Questions:

    • What is the target audience for this design document? Is it for Flask core developers, security auditors, or application developers using Flask?
    • What is the expected level of detail for threat modeling? Should it cover specific attack vectors and mitigation strategies?
    • Are there any specific compliance requirements or security standards that Flask project needs to adhere to?
    • What is the process for handling security vulnerabilities reported in Flask? Is there a public security policy or disclosure process?

  • Assumptions:

    • BUSINESS POSTURE: The primary goal of Flask is to be a secure, reliable, and easy-to-use web framework for Python developers. Security is a high priority for the project.
    • SECURITY POSTURE: Flask project follows secure development practices, including code review and vulnerability management. Security is primarily the responsibility of application developers using Flask.
    • DESIGN: Flask is designed as a microframework with a modular architecture, relying on external libraries for many functionalities. Deployment is typically containerized or on cloud platforms. Build process is automated using CI/CD pipelines.