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Okay, let's create a design document for the Parsedown project.

BUSINESS POSTURE

Parsedown is a Markdown parser library written in PHP. It's designed for speed and extensibility. The primary business goal is to provide a reliable and fast way to convert Markdown text into HTML. It's used in a wide variety of applications, from content management systems to simple websites. Given its open-source nature and wide adoption, the following business priorities and risks are identified:

Priorities:

  • Maintainability: The project must be easy to maintain and update, given its reliance by many other projects.
  • Performance: Speed of parsing is a key selling point, so performance regressions must be avoided.
  • Extensibility: The ability to extend Parsedown with custom functionality is important for its user base.
  • Compatibility: Maintaining broad compatibility with different PHP versions and environments is crucial.
  • Community: Foster a healthy open-source community to encourage contributions and bug reports.

Business Risks:

  • Security Vulnerabilities: As a parser, vulnerabilities like XSS (Cross-Site Scripting) could have significant consequences for applications using Parsedown. This is the most critical risk.
  • Reputation Damage: Security vulnerabilities or major bugs could damage the reputation of the library and lead to users switching to alternatives.
  • Maintenance Burden: If the codebase becomes difficult to maintain, it could lead to slow response times for bug fixes and security updates.
  • Dependency Issues: Reliance on outdated or vulnerable dependencies could introduce security risks.
  • Lack of Adoption: While currently popular, a decline in adoption could lead to a decrease in community support and maintenance.

SECURITY POSTURE

Existing Security Controls:

  • security control: Input Validation: Parsedown performs input validation to prevent common Markdown-related vulnerabilities. (Implemented in the Parsedown code itself.)
  • security control: Escaping: Parsedown escapes HTML entities to prevent XSS attacks. (Implemented in the Parsedown code itself.)
  • security control: Regular Updates: The project maintainer releases updates to address bugs and security vulnerabilities. (Evidenced by the GitHub repository's commit history and releases.)
  • security control: Community Scrutiny: Being open-source, the code is subject to scrutiny by the community, which can help identify vulnerabilities. (Evidenced by the GitHub issues and pull requests.)
  • security control: Safe by default: Parsedown escapes HTML by default. (Implemented in the Parsedown code itself.)

Accepted Risks:

  • accepted risk: Limited Sanitization of Custom Extensions: While Parsedown itself is secure, custom extensions created by users might introduce vulnerabilities. This is a responsibility of the extension developers.
  • accepted risk: Reliance on PHP's Security: Parsedown relies on the underlying security of the PHP environment. Vulnerabilities in PHP itself could impact Parsedown.

Recommended Security Controls:

  • security control: Content Security Policy (CSP) Guidance: Provide clear documentation and examples on how to use CSP with Parsedown to mitigate XSS risks further. This should be included in the project's README or documentation.
  • security control: Regular Security Audits: Conduct periodic security audits, either internally or by a third-party, to identify potential vulnerabilities.
  • security control: Dependency Scanning: Implement automated dependency scanning to identify and address vulnerabilities in third-party libraries.
  • security control: Fuzz Testing: Integrate fuzz testing into the development process to discover unexpected vulnerabilities.

Security Requirements:

  • Authentication: Not applicable, as Parsedown is a library and does not handle authentication.
  • Authorization: Not applicable, as Parsedown is a library and does not handle authorization.
  • Input Validation:
    • Must sanitize all Markdown input to prevent XSS vulnerabilities.
    • Must handle potentially malicious Markdown constructs safely.
    • Must provide mechanisms for users to customize input sanitization if needed (with appropriate warnings).
  • Cryptography: Not directly applicable, but if Parsedown is used to process encrypted data, it should not interfere with the encryption/decryption process. Parsedown should treat encrypted data as plain text and not attempt to interpret it.
  • Output Encoding:
    • Must properly escape HTML output to prevent XSS.
    • Should provide options for different escaping strategies (e.g., HTML entities, attribute encoding).

DESIGN

C4 CONTEXT

graph LR
    User("User") --> Parsedown("Parsedown")
    Parsedown --> WebApplication("Web Application")
    Parsedown --> CMS("CMS")
    Parsedown --> OtherApplications("Other Applications")
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Element Descriptions:

  • Element:

    • Name: User
    • Type: Person
    • Description: A person interacting with an application that uses Parsedown.
    • Responsibilities: Provides Markdown input, views HTML output.
    • Security controls: None (relies on application-level security).

  • Element:

    • Name: Parsedown
    • Type: Software System
    • Description: The Parsedown Markdown parser library.
    • Responsibilities: Converts Markdown text to HTML.
    • Security controls: Input validation, HTML escaping, safe by default.

  • Element:

    • Name: Web Application
    • Type: Software System
    • Description: A web application that utilizes Parsedown.
    • Responsibilities: Integrates Parsedown, handles user input and output, implements application-specific logic.
    • Security controls: Application-level security controls (e.g., authentication, authorization, CSP).

  • Element:

    • Name: CMS
    • Type: Software System
    • Description: A Content Management System that uses Parsedown.
    • Responsibilities: Manages content, uses Parsedown for Markdown rendering.
    • Security controls: CMS-specific security controls, plus those inherited from using Parsedown.

  • Element:

    • Name: Other Applications
    • Type: Software System
    • Description: Other types of applications that might use Parsedown (e.g., command-line tools, desktop applications).
    • Responsibilities: Varies depending on the application.
    • Security controls: Application-specific security controls.

C4 CONTAINER

Since Parsedown is a single library, the container diagram is essentially the same as the context diagram, with the addition of the PHP runtime.

graph LR
    User("User") --> WebApplication("Web Application")
    WebApplication --> Parsedown("Parsedown (PHP Library)")
    Parsedown --> PHPRUNTIME("PHP Runtime")
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Element Descriptions:

  • Element:

    • Name: User
    • Type: Person
    • Description: A person interacting with a web application.
    • Responsibilities: Provides input, views output.
    • Security controls: None (relies on application-level security).

  • Element:

    • Name: Web Application
    • Type: Software System
    • Description: A web application that utilizes Parsedown.
    • Responsibilities: Integrates Parsedown, handles user input and output.
    • Security controls: Application-level security controls (e.g., authentication, authorization, CSP).

  • Element:

    • Name: Parsedown (PHP Library)
    • Type: Container (Library)
    • Description: The Parsedown library code.
    • Responsibilities: Parses Markdown input, generates HTML output.
    • Security controls: Input validation, HTML escaping.

  • Element:

    • Name: PHP Runtime
    • Type: Container (Runtime Environment)
    • Description: The PHP runtime environment.
    • Responsibilities: Executes the Parsedown code.
    • Security controls: PHP's built-in security features, server configuration.

DEPLOYMENT

Parsedown, being a PHP library, is typically deployed as part of a larger PHP application. There are several deployment models:

  1. Traditional Web Server: The application (including Parsedown) is deployed to a web server like Apache or Nginx, with PHP configured as a module (e.g., mod_php) or via FastCGI (e.g., PHP-FPM).
  2. Cloud Platforms (PaaS): Platforms like Heroku, AWS Elastic Beanstalk, or Google App Engine provide managed environments where the application can be deployed. PHP is typically configured as a buildpack or runtime environment.
  3. Containers (Docker): The application and its dependencies (including Parsedown and PHP) are packaged into a Docker container, which can be deployed to various container orchestration platforms (e.g., Kubernetes, Docker Swarm, AWS ECS).
  4. Serverless: While less common for traditional PHP applications, it's possible to use Parsedown within a serverless function (e.g., AWS Lambda with a PHP layer).

We'll describe the Containers (Docker) deployment model in detail, as it offers good isolation and portability:

graph LR
    Developer("Developer") --> SourceCodeRepository("Source Code Repository")
    SourceCodeRepository --> CIBuildServer("CI/Build Server")
    CIBuildServer --> DockerImageRegistry("Docker Image Registry")
    DockerImageRegistry --> DeploymentEnvironment("Deployment Environment (e.g., Kubernetes)")
    DeploymentEnvironment --> WebServer("Web Server (e.g., Nginx)")
    WebServer --> PHPRUNTIME("PHP-FPM")
    PHPRUNTIME --> Parsedown("Parsedown")
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Element Descriptions:

  • Element:

    • Name: Developer
    • Type: Person
    • Description: Develops the application code that uses Parsedown.
    • Responsibilities: Writes code, commits to the repository.
    • Security controls: Code review, secure coding practices.

  • Element:

    • Name: Source Code Repository
    • Type: System
    • Description: Stores the application's source code (e.g., GitHub, GitLab).
    • Responsibilities: Version control, access control.
    • Security controls: Access controls, branch protection rules.

  • Element:

    • Name: CI/Build Server
    • Type: System
    • Description: Builds the Docker image (e.g., Jenkins, GitLab CI, GitHub Actions).
    • Responsibilities: Runs tests, builds the image, pushes to the registry.
    • Security controls: Secure build environment, dependency scanning.

  • Element:

    • Name: Docker Image Registry
    • Type: System
    • Description: Stores the built Docker image (e.g., Docker Hub, AWS ECR).
    • Responsibilities: Image storage, access control.
    • Security controls: Access controls, image scanning.

  • Element:

    • Name: Deployment Environment (e.g., Kubernetes)
    • Type: System
    • Description: Orchestrates the deployment of the Docker container.
    • Responsibilities: Manages container lifecycle, scaling, networking.
    • Security controls: Network policies, resource quotas, RBAC.

  • Element:

    • Name: Web Server (e.g., Nginx)
    • Type: Container
    • Description: Serves the web application.
    • Responsibilities: Handles HTTP requests, forwards requests to PHP-FPM.
    • Security controls: Web server configuration, TLS encryption.

  • Element:

    • Name: PHP-FPM
    • Type: Container
    • Description: Executes the PHP code.
    • Responsibilities: Processes PHP requests, interacts with Parsedown.
    • Security controls: PHP configuration, resource limits.

  • Element:

    • Name: Parsedown
    • Type: Library
    • Description: The Parsedown library.
    • Responsibilities: Parses Markdown.
    • Security controls: Input validation, HTML escaping.

BUILD

The build process for an application using Parsedown typically involves the following steps:

  1. Dependency Management: Composer is used to manage PHP dependencies, including Parsedown. The composer.json file specifies the required version of Parsedown. composer install downloads Parsedown and its dependencies into the vendor directory.
  2. Code Integration: The application code includes Parsedown using require_once 'vendor/autoload.php'; or similar.
  3. Testing: Unit tests and integration tests are run to verify the functionality of Parsedown and its integration with the application.
  4. Containerization (if applicable): A Dockerfile is used to create a Docker image. This file typically includes instructions to:
    • Use a base PHP image (e.g., php:fpm).
    • Copy the application code and the vendor directory into the image.
    • Configure the web server (e.g., Nginx) and PHP-FPM.
  5. Image Building: The Docker image is built using docker build.
  6. Image Pushing: The Docker image is pushed to a container registry (e.g., Docker Hub, AWS ECR) using docker push.
graph LR
    Developer("Developer") --> SourceCodeRepository("Source Code Repository")
    SourceCodeRepository --> Composer("Composer (Dependency Management)")
    Composer --> ParsedownLibrary("Parsedown Library (vendor directory)")
    SourceCodeRepository --> Tests("Tests (Unit, Integration)")
    Tests --> ParsedownLibrary
    SourceCodeRepository --> Dockerfile("Dockerfile")
    Dockerfile --> BuildProcess("Build Process (docker build)")
    BuildProcess --> DockerImage("Docker Image")
    DockerImage --> DockerImageRegistry("Docker Image Registry")
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Security Controls in the Build Process:

  • security control: Dependency Management with Composer: Using Composer helps ensure that the correct version of Parsedown is used and that dependencies are managed securely.
  • security control: Composer.lock: The composer.lock file locks the dependencies to specific versions, preventing unexpected updates that could introduce vulnerabilities.
  • security control: Automated Testing: Running unit and integration tests helps identify bugs and vulnerabilities early in the development process.
  • security control: Secure Dockerfile: The Dockerfile should be written securely, using minimal base images, avoiding unnecessary packages, and setting appropriate user permissions.
  • security control: Image Scanning: Docker images should be scanned for vulnerabilities before being pushed to the registry. Tools like Trivy, Clair, or Anchore can be used for this purpose.
  • security control: Supply Chain Security: Consider using tools and practices to ensure the integrity of the software supply chain, such as signing Docker images and verifying the provenance of dependencies.

RISK ASSESSMENT

Critical Business Processes:

  • Rendering Markdown content reliably and securely.
  • Maintaining the availability and performance of applications that rely on Parsedown.
  • Protecting the reputation of the Parsedown project.

Data to Protect:

  • User-provided Markdown content: Sensitivity varies depending on the application. Could range from public blog posts to private internal documents. The primary concern is preventing XSS attacks through malicious Markdown.
  • Application data: Parsedown itself doesn't store application data, but vulnerabilities in Parsedown could be exploited to gain access to application data.
  • Source code: The Parsedown source code itself is publicly available, but unauthorized modifications could introduce vulnerabilities.

QUESTIONS & ASSUMPTIONS

Questions:

  • Are there any specific compliance requirements (e.g., PCI DSS, HIPAA) that apply to applications using Parsedown?
  • What is the expected volume of Markdown content to be processed? This can impact performance considerations.
  • Are there any specific security concerns or past incidents related to the use of Markdown parsers in the organization?
  • What is the process for reporting and handling security vulnerabilities in Parsedown?

Assumptions:

  • BUSINESS POSTURE: The primary goal is to provide a fast and secure Markdown parser. The project has a moderate risk appetite, balancing security with ease of use and extensibility.
  • SECURITY POSTURE: The existing security controls are adequate for basic protection, but additional measures (CSP guidance, security audits, dependency scanning) are recommended.
  • DESIGN: The deployment model will likely involve a web server and PHP, with containerization being a preferred option for modern deployments. The build process will use Composer for dependency management.