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sec-design.md

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Okay, let's create a design document for the Matrix Synapse project, focusing on aspects relevant for threat modeling.

BUSINESS POSTURE

Matrix Synapse is a reference "homeserver" implementation for the Matrix communication protocol. The primary business goal is to provide a robust, scalable, and secure platform for decentralized, real-time communication. It aims to enable interoperable communication across different Matrix servers, fostering a federated network. Success is measured by adoption, stability, and the ability to handle large volumes of users and messages while maintaining data integrity and confidentiality. The project is open-source, so community contributions and reputation are also key.

Business Priorities:

  • Federation: Enable seamless communication between different Synapse instances and other Matrix servers.
  • Scalability: Handle a growing number of users, rooms, and messages.
  • Reliability: Provide a stable and consistently available service.
  • Security: Protect user data and communications from unauthorized access and modification.
  • Interoperability: Adhere to the Matrix specification to ensure compatibility with other Matrix clients and servers.
  • Open Source: Maintain a healthy and active open-source project.

Business Risks:

  • Data Breaches: Unauthorized access to user data (messages, profiles, etc.) due to vulnerabilities in Synapse or related infrastructure.
  • Denial of Service: Attacks that render the server unavailable to users.
  • Federation Issues: Problems with communication between servers, leading to message loss or service disruption.
  • Reputation Damage: Security incidents or prolonged outages could damage the reputation of Synapse and the Matrix protocol.
  • Spam and Abuse: Malicious users exploiting the platform for spam, harassment, or other abusive activities.
  • Compliance Violations: Failure to comply with relevant data privacy regulations (e.g., GDPR).

SECURITY POSTURE

Existing Security Controls:

  • security control: HTTPS: Communication between clients and the server, and between servers, is encrypted using HTTPS (TLS). Implemented in Synapse server and client configurations.
  • security control: Access Control: Synapse implements access control mechanisms to restrict access to rooms and data based on user permissions. Described in Matrix specification and implemented in Synapse code.
  • security control: Federation Security: Synapse uses TLS and digital signatures to secure communication with other Matrix servers. Described in Matrix specification and implemented in Synapse code.
  • security control: Rate Limiting: Synapse implements rate limiting to mitigate denial-of-service attacks and abuse. Implemented in Synapse configuration and code.
  • security control: Input Validation: Synapse performs input validation to prevent various injection attacks. Implemented in Synapse code.
  • security control: Authentication: User authentication via passwords, tokens, or single sign-on (SSO). Implemented in Synapse code and configuration.
  • security control: End-to-End Encryption (E2EE): While not directly a Synapse feature, Synapse supports E2EE implemented by Matrix clients. Synapse handles encrypted event transport.

Accepted Risks:

  • accepted risk: Complexity of Federation: The federated nature of Matrix introduces complexity, making it challenging to ensure consistent security across all servers.
  • accepted risk: Reliance on Third-Party Libraries: Synapse depends on various third-party libraries, which could introduce vulnerabilities.
  • accepted risk: Client-Side Security: The security of end-to-end encryption relies heavily on the security of the client applications.

Recommended Security Controls:

  • Regular Security Audits: Conduct regular independent security audits of the Synapse codebase and infrastructure.
  • Vulnerability Disclosure Program: Implement a formal vulnerability disclosure program to encourage responsible reporting of security issues.
  • Content Security Policy (CSP): Implement a strong CSP to mitigate cross-site scripting (XSS) vulnerabilities.
  • Intrusion Detection System (IDS): Deploy an IDS to monitor for and alert on suspicious activity.
  • Database Encryption at Rest: Encrypt the database at rest to protect data in case of server compromise.

Security Requirements:

  • Authentication:

    • Support for strong password policies.
    • Support for multi-factor authentication (MFA).
    • Secure storage of passwords (e.g., using bcrypt or similar).
    • Secure session management.
    • Support for Single Sign-On (SSO) with secure protocols (e.g., OpenID Connect).

  • Authorization:

    • Fine-grained access control to rooms and data based on user roles and permissions.
    • Secure implementation of the Matrix access control model.
    • Regular review of access control policies.

  • Input Validation:

    • Strict validation of all user inputs to prevent injection attacks (e.g., XSS, SQL injection).
    • Use of allow-lists rather than block-lists where possible.
    • Validation of data received from other Matrix servers.

  • Cryptography:

    • Use of strong, well-vetted cryptographic algorithms and libraries.
    • Secure key management practices.
    • Regular review of cryptographic implementations.
    • Support for Perfect Forward Secrecy (PFS) in TLS configurations.

DESIGN

C4 CONTEXT

graph LR
    A["User"] --> B("Matrix Client");
    B <--> C("Synapse Homeserver");
    C <--> D("Other Matrix Homeservers");
    C <--> E("Identity Server");
    C <--> F("Application Services");
    B <--> E;
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Element Descriptions:

  • Element:

    • Name: User
    • Type: Person
    • Description: A person who uses a Matrix client to communicate.
    • Responsibilities: Sending and receiving messages, managing their profile, joining and leaving rooms.
    • Security controls: Strong passwords, MFA (if enabled), client-side security measures.

  • Element:

    • Name: Matrix Client
    • Type: Software System
    • Description: A client application used to access the Matrix network (e.g., Element, Fluffychat).
    • Responsibilities: Connecting to a homeserver, displaying the user interface, handling end-to-end encryption (if enabled).
    • Security controls: Secure coding practices, protection against XSS and other client-side vulnerabilities, secure storage of encryption keys.

  • Element:

    • Name: Synapse Homeserver
    • Type: Software System
    • Description: The Matrix Synapse homeserver implementation.
    • Responsibilities: Managing user accounts, storing messages, handling room membership, federating with other homeservers.
    • Security controls: HTTPS, access control, rate limiting, input validation, federation security.

  • Element:

    • Name: Other Matrix Homeservers
    • Type: Software System
    • Description: Other Matrix homeservers that Synapse federates with.
    • Responsibilities: Same as Synapse Homeserver.
    • Security controls: Should implement similar security controls as Synapse, but this is outside the direct control of the Synapse project.

  • Element:

    • Name: Identity Server
    • Type: Software System
    • Description: An optional server that maps third-party identifiers (e.g., email addresses, phone numbers) to Matrix user IDs.
    • Responsibilities: Handling identity verification and lookup requests.
    • Security controls: Secure communication with homeservers and clients, protection of user identity data.

  • Element:

    • Name: Application Services
    • Type: Software System
    • Description: Optional services that extend the functionality of Matrix (e.g., bridges to other communication platforms).
    • Responsibilities: Varies depending on the specific application service.
    • Security controls: Secure communication with the homeserver, appropriate access controls.

C4 CONTAINER

graph LR
    A["Matrix Client"] <--> B("Web Server (nginx/Apache)");
    B <--> C("Synapse Application Server (Python/Twisted)");
    C <--> D("Database (PostgreSQL)");
    C <--> E("Federation API");
    E <--> F("Other Matrix Homeservers");
    C <--> G("Media Repository");
    G <--> D;
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Element Descriptions:

  • Element:

    • Name: Matrix Client
    • Type: Software System
    • Description: A client application used to access the Matrix network.
    • Responsibilities: Connecting to a homeserver, displaying the user interface, handling end-to-end encryption (if enabled).
    • Security controls: Secure coding practices, protection against XSS and other client-side vulnerabilities, secure storage of encryption keys.

  • Element:

    • Name: Web Server (nginx/Apache)
    • Type: Software System
    • Description: A reverse proxy server that handles incoming requests and forwards them to the Synapse application server.
    • Responsibilities: TLS termination, load balancing, serving static content.
    • Security controls: HTTPS configuration, protection against common web vulnerabilities (e.g., DDoS, request smuggling).

  • Element:

    • Name: Synapse Application Server (Python/Twisted)
    • Type: Software System
    • Description: The core Synapse application, written in Python using the Twisted framework.
    • Responsibilities: Handling client requests, processing events, managing room state, interacting with the database and other services.
    • Security controls: Input validation, access control, authentication, rate limiting.

  • Element:

    • Name: Database (PostgreSQL)
    • Type: Database
    • Description: A PostgreSQL database that stores user data, messages, room state, and other persistent data.
    • Responsibilities: Data storage and retrieval.
    • Security controls: Database access control, encryption at rest (recommended), regular backups.

  • Element:

    • Name: Federation API
    • Type: API
    • Description: An API used for communication with other Matrix homeservers.
    • Responsibilities: Sending and receiving events, handling user presence, exchanging room information.
    • Security controls: HTTPS, digital signatures, access control.

  • Element:

    • Name: Other Matrix Homeservers
    • Type: Software System
    • Description: Other Matrix homeservers that Synapse federates with.
    • Responsibilities: Same as Synapse Homeserver.
    • Security controls: Should implement similar security controls as Synapse.

  • Element:

    • Name: Media Repository
    • Type: Software System
    • Description: Stores and serves media files (images, videos, etc.) uploaded by users.
    • Responsibilities: Storing and retrieving media files.
    • Security controls: Access control, virus scanning (recommended), content type validation.

DEPLOYMENT

Possible Deployment Solutions:

  1. Bare Metal/Virtual Machine: Synapse and its dependencies are installed directly on a physical or virtual server.
  2. Docker: Synapse and its dependencies are packaged as Docker containers.
  3. Kubernetes: Synapse and its dependencies are deployed as a Kubernetes cluster.
  4. Ansible: Using Ansible playbooks to automate deployment.

Chosen Solution (for detailed description): Docker

graph LR
    A["Docker Host"] --> B("Synapse Container");
    A --> C("PostgreSQL Container");
    A --> D("nginx Container");
    B <--> C;
    D <--> B;
    A --> E("Media Volume");
    B <--> E;
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Element Descriptions:

  • Element:

    • Name: Docker Host
    • Type: Infrastructure
    • Description: The physical or virtual server that runs the Docker engine.
    • Responsibilities: Running Docker containers.
    • Security controls: Operating system hardening, firewall, regular security updates.

  • Element:

    • Name: Synapse Container
    • Type: Container
    • Description: A Docker container running the Synapse application server.
    • Responsibilities: Handling client requests, processing events, managing room state.
    • Security controls: Minimal base image, regular security updates, running as a non-root user.

  • Element:

    • Name: PostgreSQL Container
    • Type: Container
    • Description: A Docker container running the PostgreSQL database.
    • Responsibilities: Data storage and retrieval.
    • Security controls: Minimal base image, secure configuration, regular security updates, running as a non-root user.

  • Element:

    • Name: nginx Container
    • Type: Container
    • Description: A Docker container running the nginx reverse proxy.
    • Responsibilities: TLS termination, load balancing, serving static content.
    • Security controls: Minimal base image, secure configuration, regular security updates, running as a non-root user.

  • Element:

    • Name: Media Volume
    • Type: Storage
    • Description: A Docker volume used to store media files.
    • Responsibilities: Persistent storage for media files.
    • Security controls: Access control, regular backups.

BUILD

The Synapse build process typically involves the following steps:

  1. Developer: A developer writes code and pushes it to the Git repository (GitHub).
  2. Continuous Integration (CI): A CI system (e.g., GitHub Actions) is triggered by the push.
  3. Build: The CI system checks out the code, installs dependencies, and builds the Synapse package.
  4. Testing: The CI system runs unit tests, integration tests, and linters.
  5. Packaging: If the tests pass, the CI system creates a Docker image containing the Synapse application.
  6. Publish: The Docker image is pushed to a container registry (e.g., Docker Hub).
graph LR
    A["Developer"] --> B("GitHub Repository");
    B --> C("GitHub Actions (CI)");
    C --> D("Build Server");
    D --> E("Unit Tests");
    D --> F("Integration Tests");
    D --> G("Linters");
    E --> H{"Pass/Fail"};
    F --> H;
    G --> H;
    H -- "Pass" --> I("Docker Build");
    H -- "Fail" --> J("Notification");
    I --> K("Docker Image");
    K --> L("Container Registry");
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Security Controls:

  • Supply Chain Security: Use of signed commits, dependency verification, and vulnerability scanning of dependencies.
  • Build Automation: Automated build process using GitHub Actions to ensure consistency and repeatability.
  • Security Checks:
    • Linters: Use of linters (e.g., pylint, flake8) to enforce coding standards and identify potential security issues.
    • Static Analysis Security Testing (SAST): Integration of SAST tools (e.g., Bandit) into the CI pipeline to scan for vulnerabilities in the code.
    • Software Composition Analysis (SCA): Use of SCA tools to identify and manage vulnerabilities in third-party libraries.
  • Least Privilege: Build processes should run with the least necessary privileges.
  • Reproducible Builds: Aim for reproducible builds to ensure that the same source code always produces the same binary.

RISK ASSESSMENT

Critical Business Processes:

  • Real-time communication between users.
  • Federated communication between Matrix servers.
  • User account management.
  • Media sharing.

Data Sensitivity:

  • Messages: Highly sensitive, especially if not end-to-end encrypted.
  • User Profile Data: Potentially sensitive, depending on the information provided by the user.
  • Room Metadata: Moderately sensitive, as it can reveal information about user activity and relationships.
  • Media Files: Sensitivity varies depending on the content.
  • Authentication Credentials: Highly sensitive.

QUESTIONS & ASSUMPTIONS

Questions:

  • What is the specific threat model used by the Matrix Synapse development team?
  • What are the current procedures for handling security incidents?
  • What are the plans for implementing additional security features, such as database encryption at rest?
  • What is the process for reviewing and approving changes to the codebase, particularly those related to security?
  • How are secrets (e.g., API keys, database passwords) managed in the deployment environment?
  • What monitoring and logging capabilities are in place to detect and respond to security events?

Assumptions:

  • BUSINESS POSTURE: The primary business goal is to provide a secure and reliable communication platform.
  • SECURITY POSTURE: The development team follows secure coding practices and regularly updates dependencies.
  • DESIGN: The deployment environment is properly secured and monitored. The database is backed up regularly.
  • DESIGN: The use of Docker containers is the preferred deployment method.
  • DESIGN: GitHub Actions is used for continuous integration.