sec-design.md

BUSINESS POSTURE

Lemmy is a federated link aggregator, aiming to provide a decentralized alternative to platforms like Reddit. It prioritizes user privacy and community control by being open-source and part of the Fediverse.

• Business priorities and goals:

  • Provide a decentralized social media platform.
  • Offer an alternative to centralized platforms with a focus on user privacy and community governance.
  • Foster a community-driven and open-source ecosystem.
  • Enable users to control their data and online experience.
  • Support interoperability with other Fediverse platforms.

• Business risks:

  • Moderation challenges in a decentralized environment.
  • Difficulty in achieving network effects and user adoption compared to established centralized platforms.
  • Potential for misuse and abuse due to decentralization and open nature.
  • Reliance on community contributions for development and maintenance.
  • Complexity of managing a federated system and ensuring interoperability.

SECURITY POSTURE

Lemmy, being an open-source project, benefits from community scrutiny, which can contribute to identifying and addressing security vulnerabilities. As a federated platform handling user-generated content and personal data, security is crucial.

• Existing security controls:

  • security control: HTTPS enforced for web traffic (standard web server configuration). Implemented in: Deployment configuration (e.g., reverse proxy setup).
  • security control: Regular software updates for dependencies (Rust crates, Node.js packages). Implemented in: Project's dependency management (Cargo.toml, package.json) and CI/CD pipelines.
  • security control: Input sanitization and output encoding to prevent common web vulnerabilities (likely implemented within the Rust backend and Typescript frontend code). Implemented in: Source code of backend and frontend applications.
  • security control: Rate limiting to mitigate abuse and denial-of-service attacks (likely implemented in the backend application or reverse proxy). Implemented in: Backend application code or reverse proxy configuration.
  • accepted risk: Potential vulnerabilities in third-party dependencies. Mitigation: Regular dependency updates and vulnerability scanning.
  • accepted risk: Community-driven security audits might be less frequent or comprehensive than professional audits. Mitigation: Encourage community contributions and seek external security audits when feasible.

• Recommended security controls:

  • security control: Implement a robust Content Security Policy (CSP) to mitigate Cross-Site Scripting (XSS) attacks.
  • security control: Regularly perform static and dynamic application security testing (SAST/DAST) on both backend and frontend code.
  • security control: Implement database security best practices, including principle of least privilege for database access and regular backups.
  • security control: Implement comprehensive logging and monitoring for security events and anomalies.
  • security control: Conduct regular security audits and penetration testing, especially before major releases.
  • security control: Implement a vulnerability disclosure program to encourage responsible reporting of security issues.
  • security control: Secure secret management for API keys, database credentials, and other sensitive information.

• Security requirements:

  • Authentication:
    • Requirement: Secure user authentication mechanism to verify user identity.
    • Requirement: Support for password-based authentication and potentially federated authentication (e.g., OAuth, WebAuthn).
    • Requirement: Protection against brute-force attacks on login endpoints (e.g., account lockout, rate limiting).
  • Authorization:
    • Requirement: Role-based access control (RBAC) to manage user permissions and access to features (e.g., admin, moderator, user).
    • Requirement: Fine-grained authorization to control access to specific resources and actions (e.g., posting, commenting, moderating).
    • Requirement: Consistent authorization enforcement across backend and frontend.
  • Input validation:
    • Requirement: Server-side input validation for all user-provided data to prevent injection attacks (e.g., SQL injection, command injection, XSS).
    • Requirement: Client-side input validation for user experience and early error detection, but not as a primary security control.
    • Requirement: Validation of file uploads to prevent malicious file uploads.
  • Cryptography:
    • Requirement: Use of strong encryption algorithms for sensitive data at rest and in transit.
    • Requirement: Secure storage of cryptographic keys and secrets.
    • Requirement: Proper implementation of cryptographic protocols (e.g., TLS for HTTPS).
    • Requirement: Hashing of passwords using strong hashing algorithms with salt.

DESIGN

C4 CONTEXT

flowchart LR
    subgraph "Lemmy System"
        A("Lemmy Instance")
    end
    B("Users") -- "Uses" --> A
    C("Other Fediverse Instances") -- "Federates with" --> A
    D("Database Server") -- "Stores Data" --> A
    E("Object Storage") -- "Stores Media" --> A
    F("Email Server") -- "Sends Notifications" --> A
    G("Moderators") -- "Moderates Content" --> A
    style A fill:#f9f,stroke:#333,stroke-width:2px

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• Context Diagram Elements:

  • Element:

    • Name: Lemmy Instance
    • Type: Software System
    • Description: The Lemmy application itself, providing link aggregation and social networking features within the Fediverse.
    • Responsibilities:
      • Handles user requests (web and API).
      • Manages content creation, storage, and retrieval.
      • Implements federation with other Fediverse instances.
      • Enforces security controls and business logic.
    • Security controls:
      • Input validation.
      • Authorization.
      • Authentication.
      • Rate limiting.
      • HTTPS encryption.
      • Logging and monitoring.

  • Element:

    • Name: Users
    • Type: Person
    • Description: Individuals who interact with the Lemmy instance to browse content, create posts, comments, and communities.
    • Responsibilities:
      • Accessing Lemmy through web browsers or mobile applications.
      • Creating and consuming content.
      • Interacting with other users and communities.
    • Security controls:
      • Strong passwords.
      • Multi-factor authentication (if implemented).
      • Awareness of phishing and social engineering attacks.

  • Element:

    • Name: Other Fediverse Instances
    • Type: Software System
    • Description: Other instances of Lemmy or compatible Fediverse platforms (e.g., Mastodon, Pleroma) that Lemmy federates with.
    • Responsibilities:
      • Exchanging data with the Lemmy instance according to the ActivityPub protocol.
      • Participating in federated timelines and communities.
    • Security controls:
      • Adherence to Fediverse protocols and security best practices.
      • Instance-level security configurations.

  • Element:

    • Name: Database Server
    • Type: Software System
    • Description: A database system (e.g., PostgreSQL) used by Lemmy to store persistent data, including user accounts, posts, comments, communities, and relationships.
    • Responsibilities:
      • Storing and retrieving data for the Lemmy application.
      • Ensuring data integrity and availability.
      • Managing database access and security.
    • Security controls:
      • Access control lists (ACLs).
      • Encryption at rest (if configured).
      • Regular backups.
      • Database hardening.

  • Element:

    • Name: Object Storage
    • Type: Software System
    • Description: Object storage (e.g., AWS S3, MinIO) used to store media files, such as images and videos uploaded by users.
    • Responsibilities:
      • Storing and serving media files.
      • Ensuring data durability and availability.
      • Managing access to stored objects.
    • Security controls:
      • Access control policies.
      • Encryption at rest and in transit.
      • Regular backups.

  • Element:

    • Name: Email Server
    • Type: Software System
    • Description: An email server (e.g., SMTP server) used by Lemmy to send email notifications to users, such as password reset emails and subscription updates.
    • Responsibilities:
      • Sending emails on behalf of the Lemmy instance.
      • Ensuring email delivery and reliability.
    • Security controls:
      • SMTP authentication.
      • TLS encryption for email transmission.
      • SPF, DKIM, and DMARC records to prevent email spoofing.

  • Element:

    • Name: Moderators
    • Type: Person
    • Description: Users with elevated privileges who are responsible for moderating content and enforcing community guidelines within Lemmy instances.
    • Responsibilities:
      • Reviewing and moderating user-generated content.
      • Enforcing community rules and guidelines.
      • Managing user reports and appeals.
    • Security controls:
      • Strong authentication for moderator accounts.
      • Audit logging of moderator actions.
      • Principle of least privilege for moderator roles.

C4 CONTAINER

flowchart LR
    subgraph "Lemmy Instance"
        A("Lemmy Backend" <br> "Rust")
        B("Lemmy Frontend" <br> "Typescript/React")
    end
    C("Web Browser") -- "HTTPS" --> B
    B -- "HTTPS/API" --> A
    A -- "Database Connection" --> D("Database Server" <br> "PostgreSQL")
    A -- "Object Storage API" --> E("Object Storage" <br> "S3/MinIO")
    A -- "SMTP" --> F("Email Server")
    style A fill:#f9f,stroke:#333,stroke-width:2px
    style B fill:#f9f,stroke:#333,stroke-width:2px

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• Container Diagram Elements:

  • Element:

    • Name: Lemmy Backend
    • Type: Container - Application
    • Description: The backend application of Lemmy, written in Rust. It handles API requests, business logic, data persistence, federation, and background tasks.
    • Responsibilities:
      • API endpoint for frontend and other systems.
      • User authentication and authorization.
      • Content management and moderation logic.
      • Federation with other Fediverse instances (ActivityPub).
      • Database interaction.
      • Object storage interaction.
      • Email notifications.
    • Security controls:
      • Input validation.
      • Authorization checks.
      • Secure API design.
      • Rate limiting.
      • Database connection security.
      • Secure handling of secrets.
      • Logging and monitoring.

  • Element:

    • Name: Lemmy Frontend
    • Type: Container - Application
    • Description: The frontend application of Lemmy, written in Typescript and React. It provides the user interface for interacting with Lemmy through web browsers.
    • Responsibilities:
      • User interface for browsing content, creating posts, comments, and communities.
      • Rendering data received from the backend API.
      • Handling user interactions and events.
      • Client-side input validation.
    • Security controls:
      • Output encoding to prevent XSS.
      • Content Security Policy (CSP).
      • Secure handling of user sessions (cookies, tokens).
      • Regular updates of frontend dependencies.

  • Element:

    • Name: Web Browser
    • Type: Container - Client
    • Description: User's web browser used to access the Lemmy frontend application.
    • Responsibilities:
      • Rendering the Lemmy frontend application.
      • Sending HTTP requests to the frontend application.
      • Displaying content to the user.
    • Security controls:
      • Browser security features (e.g., same-origin policy, XSS protection).
      • User awareness of browser security settings and extensions.

  • Element:

    • Name: Database Server (PostgreSQL)
    • Type: Container - Database
    • Description: PostgreSQL database server used by the Lemmy backend to store persistent data.
    • Responsibilities:
      • Persistent storage of application data.
      • Data retrieval and querying.
      • Data integrity and consistency.
    • Security controls:
      • Database access control.
      • Database hardening.
      • Encryption at rest (if configured).
      • Regular backups.

  • Element:

    • Name: Object Storage (S3/MinIO)
    • Type: Container - Storage
    • Description: Object storage service (e.g., AWS S3, MinIO) used to store media files.
    • Responsibilities:
      • Storage of media files.
      • Serving media files to users.
      • Data durability and availability.
    • Security controls:
      • Access control policies.
      • Encryption at rest and in transit.
      • Regular backups.

  • Element:

    • Name: Email Server
    • Type: Container - External System
    • Description: External email server used by the Lemmy backend to send email notifications.
    • Responsibilities:
      • Sending emails.
      • Email delivery.
    • Security controls:
      • SMTP authentication.
      • TLS encryption for email transmission.
      • SPF, DKIM, and DMARC records.

DEPLOYMENT

Lemmy can be deployed in various environments, from single-server setups to more complex, scalable architectures. A common deployment architecture involves using Docker containers and a reverse proxy like Nginx.

• Deployment Architecture: Dockerized deployment on a single server or cluster.

flowchart LR
    subgraph "Server"
        A("Reverse Proxy" <br> "Nginx")
        B("Lemmy Backend Container")
        C("Lemmy Frontend Container")
        D("Database Container" <br> "PostgreSQL")
        E("Object Storage Container" <br> "MinIO")
    end
    F("Internet") -- "HTTPS (443)" --> A
    A -- "HTTP (Backend Port)" --> B
    A -- "HTTP (Frontend Port)" --> C
    B -- "Database Port" --> D
    B -- "Object Storage Port" --> E
    style A fill:#f9f,stroke:#333,stroke-width:2px
    style B fill:#f9f,stroke:#333,stroke-width:2px
    style C fill:#f9f,stroke:#333,stroke-width:2px
    style D fill:#f9f,stroke:#333,stroke-width:2px
    style E fill:#f9f,stroke:#333,stroke-width:2px

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• Deployment Diagram Elements:

  • Element:

    • Name: Server
    • Type: Infrastructure - Server
    • Description: A physical or virtual server hosting the Lemmy instance.
    • Responsibilities:
      • Providing the infrastructure for running Lemmy containers.
      • Network connectivity.
      • Resource allocation (CPU, memory, storage).
    • Security controls:
      • Operating system hardening.
      • Firewall configuration.
      • Regular security patching.
      • Intrusion detection/prevention systems (IDS/IPS).

  • Element:

    • Name: Reverse Proxy (Nginx)
    • Type: Infrastructure - Software
    • Description: Nginx reverse proxy server handling incoming HTTP/HTTPS requests, SSL termination, and routing traffic to backend and frontend containers.
    • Responsibilities:
      • SSL/TLS termination.
      • Routing requests to backend and frontend containers.
      • Load balancing (if multiple backend/frontend instances).
      • Web Application Firewall (WAF) capabilities (if configured).
      • Rate limiting.
    • Security controls:
      • HTTPS configuration.
      • Web Application Firewall (WAF) rules (if used).
      • Rate limiting configuration.
      • Regular security updates.

  • Element:

    • Name: Lemmy Backend Container
    • Type: Container - Docker Container
    • Description: Docker container running the Lemmy backend application.
    • Responsibilities:
      • Running the Lemmy backend application.
      • Exposing backend API.
    • Security controls:
      • Container image security scanning.
      • Principle of least privilege for container runtime.
      • Resource limits for container.

  • Element:

    • Name: Lemmy Frontend Container
    • Type: Container - Docker Container
    • Description: Docker container running the Lemmy frontend application.
    • Responsibilities:
      • Running the Lemmy frontend application.
      • Serving static frontend assets.
    • Security controls:
      • Container image security scanning.
      • Principle of least privilege for container runtime.
      • Resource limits for container.

  • Element:

    • Name: Database Container (PostgreSQL)
    • Type: Container - Docker Container
    • Description: Docker container running the PostgreSQL database server.
    • Responsibilities:
      • Running the PostgreSQL database server.
      • Persistent data storage.
    • Security controls:
      • Database container image security scanning.
      • Database access control within container.
      • Volume encryption for persistent data (if needed).
      • Regular backups.

  • Element:

    • Name: Object Storage Container (MinIO)
    • Type: Container - Docker Container
    • Description: Docker container running the MinIO object storage server (or using external service like AWS S3).
    • Responsibilities:
      • Running the object storage server.
      • Storing media files.
    • Security controls:
      • Object storage container image security scanning.
      • Access control policies within object storage.
      • Encryption at rest and in transit.
      • Regular backups.

  • Element:

    • Name: Internet
    • Type: Environment - External Network
    • Description: The public internet from which users access the Lemmy instance.
    • Responsibilities:
      • Providing network connectivity for users.
    • Security controls:
      • No direct control from Lemmy instance, rely on network security best practices and user awareness.

BUILD

The build process for Lemmy likely involves compiling the Rust backend, building the Typescript frontend, and creating Docker images. A typical CI/CD pipeline using GitHub Actions could be used for automation.

flowchart LR
    A("Developer") -- "Code Changes" --> B("GitHub Repository")
    B -- "Webhook" --> C("GitHub Actions CI")
    subgraph "GitHub Actions CI"
        D("Build Backend" <br> "Rust Compilation")
        E("Build Frontend" <br> "Typescript Build")
        F("Run Tests" <br> "Unit & Integration Tests")
        G("Security Scans" <br> "SAST, Dependency Scan")
        H("Build Docker Images")
    end
    C --> D --> E --> F --> G --> H
    H -- "Push Images" --> I("Container Registry" <br> "Docker Hub/GHCR")
    style C fill:#f9f,stroke:#333,stroke-width:2px
    style D fill:#f9f,stroke:#333,stroke-width:2px
    style E fill:#f9f,stroke:#333,stroke-width:2px
    style F fill:#f9f,stroke:#333,stroke-width:2px
    style G fill:#f9f,stroke:#333,stroke-width:2px
    style H fill:#f9f,stroke:#333,stroke-width:2px
    style I fill:#f9f,stroke:#333,stroke-width:2px

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• Build Process Elements:

  • Element:

    • Name: Developer
    • Type: Person
    • Description: Software developers contributing code to the Lemmy project.
    • Responsibilities:
      • Writing and committing code changes.
      • Performing local testing.
      • Code reviews.
    • Security controls:
      • Secure coding practices.
      • Code review process.
      • Access control to the code repository.

  • Element:

    • Name: GitHub Repository
    • Type: Software System - Version Control
    • Description: GitHub repository hosting the Lemmy source code.
    • Responsibilities:
      • Version control of source code.
      • Collaboration platform for developers.
      • Triggering CI/CD pipelines.
    • Security controls:
      • Access control to the repository.
      • Branch protection rules.
      • Audit logging of repository actions.

  • Element:

    • Name: GitHub Actions CI
    • Type: Software System - CI/CD
    • Description: GitHub Actions workflows automating the build, test, and deployment process.
    • Responsibilities:
      • Automated build process.
      • Running tests.
      • Performing security scans.
      • Building and publishing Docker images.
    • Security controls:
      • Secure CI/CD pipeline configuration.
      • Secret management for CI/CD workflows.
      • Isolation of build environments.
      • Audit logging of CI/CD actions.

  • Element:

    • Name: Build Backend (Rust Compilation)
    • Type: Build Step
    • Description: Step in the CI/CD pipeline that compiles the Rust backend code.
    • Responsibilities:
      • Compiling Rust code into executable binaries.
      • Dependency resolution.
    • Security controls:
      • Use of trusted build environments.
      • Dependency vulnerability scanning.

  • Element:

    • Name: Build Frontend (Typescript Build)
    • Type: Build Step
    • Description: Step in the CI/CD pipeline that builds the Typescript frontend code.
    • Responsibilities:
      • Compiling Typescript code.
      • Bundling frontend assets.
    • Security controls:
      • Use of trusted build environments.
      • Dependency vulnerability scanning.

  • Element:

    • Name: Run Tests (Unit & Integration Tests)
    • Type: Build Step
    • Description: Step in the CI/CD pipeline that executes unit and integration tests.
    • Responsibilities:
      • Automated testing of code functionality.
      • Identifying and preventing regressions.
    • Security controls:
      • Secure test environments.
      • Test coverage for security-relevant code.

  • Element:

    • Name: Security Scans (SAST, Dependency Scan)
    • Type: Build Step
    • Description: Step in the CI/CD pipeline that performs static application security testing (SAST) and dependency vulnerability scanning.
    • Responsibilities:
      • Identifying potential security vulnerabilities in code and dependencies.
      • Generating security reports.
    • Security controls:
      • Integration of SAST and dependency scanning tools.
      • Configuration of security scanning tools.
      • Review and remediation of security findings.

  • Element:

    • Name: Build Docker Images
    • Type: Build Step
    • Description: Step in the CI/CD pipeline that builds Docker images for the backend and frontend applications.
    • Responsibilities:
      • Creating container images.
      • Image optimization.
    • Security controls:
      • Base image selection and hardening.
      • Minimizing image size.
      • Security scanning of container images.

  • Element:

    • Name: Container Registry (Docker Hub/GHCR)
    • Type: Software System - Container Registry
    • Description: Container registry (e.g., Docker Hub, GitHub Container Registry) used to store and distribute Docker images.
    • Responsibilities:
      • Storing container images.
      • Providing access to container images for deployment.
    • Security controls:
      • Access control to the container registry.
      • Image signing and verification.
      • Vulnerability scanning of stored images.

RISK ASSESSMENT

• Critical business processes:

  • User registration and login.
  • Content creation and moderation (posts, comments, communities).
  • Federation with other instances.
  • User data management.
  • Notification delivery.

• Data sensitivity:

  • User credentials (passwords, potentially federated identities): Highly sensitive. Requires strong encryption and secure storage.
  • User profile information (username, email, bio): Sensitive. Requires protection against unauthorized access and disclosure.
  • User-generated content (posts, comments, messages): Moderately sensitive. Requires moderation and protection against misuse and abuse.
  • IP addresses and activity logs: Moderately sensitive. Can be used for abuse detection and security monitoring, but also raise privacy concerns.

QUESTIONS & ASSUMPTIONS

• Questions:

  • What is the intended scale of deployment (number of users, instances)?
  • Are there specific compliance requirements (e.g., GDPR, HIPAA)?
  • What is the organization's risk tolerance?
  • Are there existing security policies or standards that need to be followed?
  • What are the performance and availability requirements?
  • Is there a dedicated security team or person responsible for security?

• Assumptions:

  • The project aims for a reasonably secure platform, considering it handles user data and content.
  • Standard web security best practices are intended to be followed.
  • The deployment environment is assumed to be a standard cloud or server infrastructure.
  • The project is open to implementing recommended security controls.
  • The target audience is general internet users interested in decentralized social media.