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sec-design.md

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

BUSINESS POSTURE

Serde is a framework for serializing and deserializing Rust data structures efficiently and generically. It's a foundational library used by a vast number of Rust projects, ranging from small utilities to large-scale applications and services.

Priorities and Goals:

  • Performance: Serialization and deserialization speed are critical. Slowdowns in Serde can have cascading performance impacts on dependent projects.
  • Correctness: Data integrity is paramount. Incorrect serialization or deserialization can lead to data corruption, crashes, or security vulnerabilities.
  • Ease of Use: Serde aims to be easy to use and integrate into Rust projects, minimizing the boilerplate code required for serialization.
  • Generality: Support a wide variety of data formats (JSON, YAML, Bincode, etc.) and custom data structures.
  • Maintainability: The codebase should be maintainable and extensible to support new formats and features.
  • Security: Prevent vulnerabilities that could be exploited through malicious input during deserialization.

Most Important Business Risks:

  • Denial of Service (DoS): Maliciously crafted input could cause excessive resource consumption (CPU, memory) during deserialization, leading to a denial of service.
  • Remote Code Execution (RCE): Vulnerabilities in deserialization logic, especially with formats that support custom code execution (e.g., Pickle in Python, though Serde avoids this by design), could lead to RCE. This is a critical risk, even if Serde's design mitigates it.
  • Data Corruption: Bugs in Serde could lead to incorrect serialization or deserialization, resulting in data loss or corruption in applications that rely on it.
  • Supply Chain Attacks: Compromise of the Serde codebase or its dependencies could introduce vulnerabilities into a vast number of downstream projects.
  • Ecosystem Fragmentation: If Serde were to become unmaintained or significantly flawed, it could damage the Rust ecosystem due to its widespread use.

SECURITY POSTURE

Existing Security Controls:

  • security control: Strong Typing (Rust): The Rust language itself provides strong type safety and memory safety, preventing many common vulnerabilities like buffer overflows. Implemented in: Rust language.
  • security control: No unsafe in core serialization logic: Serde's core design avoids unsafe Rust code as much as possible, reducing the risk of memory safety issues. Implemented in: Serde codebase.
  • security control: Extensive Testing: Serde has a comprehensive test suite, including unit tests, integration tests, and fuzz testing. Implemented in: CI/CD pipeline, test suite.
  • security control: Fuzz Testing: Serde uses fuzz testing (e.g., with cargo fuzz) to discover potential vulnerabilities by providing random inputs. Implemented in: CI/CD pipeline, fuzzing setup.
  • security control: Dependency Management (Cargo): Rust's package manager, Cargo, helps manage dependencies and their versions, reducing the risk of using outdated or vulnerable libraries. Implemented in: Cargo.toml, Cargo.lock.
  • security control: Code Reviews: All changes to Serde go through code review by maintainers. Implemented in: GitHub pull request process.
  • security control: Clippy Lints: Serde uses Clippy, a collection of lints to catch common mistakes and improve the code. Implemented in: CI/CD pipeline, Clippy configuration.
  • security control: MIRI: Use of MIRI to detect undefined behavior. Implemented in: CI/CD pipeline.

Accepted Risks:

  • accepted risk: Performance trade-offs: Some security measures (e.g., extensive validation) might have performance implications. Serde balances security with performance.
  • accepted risk: Complexity: The generic nature of Serde and its support for many formats introduce complexity, which can increase the risk of subtle bugs.
  • accepted risk: Reliance on Data Format Implementations: Serde relies on external crates for specific data formats (e.g., serde_json). Vulnerabilities in these crates could impact Serde.

Recommended Security Controls:

  • security control: Regular Security Audits: Conduct periodic security audits by external experts to identify potential vulnerabilities.
  • security control: Supply Chain Security Measures: Implement measures to verify the integrity of dependencies and prevent supply chain attacks (e.g., software bill of materials, code signing).
  • security control: Sandboxing (Optional): For extremely high-security environments, consider sandboxing the deserialization process, although this would likely have significant performance implications.

Security Requirements:

  • Authentication: Not directly applicable to Serde itself, as it's a library, not a service. Authentication is the responsibility of applications using Serde.
  • Authorization: Not directly applicable to Serde. Authorization is the responsibility of applications using Serde.
  • Input Validation:
    • Data format validation: Each data format implementation (e.g., serde_json) must validate the input according to the format's specification.
    • Length limits: Implement configurable limits on the size of data structures (e.g., strings, arrays) to prevent denial-of-service attacks.
    • Recursion depth limits: Limit the depth of nested data structures to prevent stack overflow errors.
    • Type validation: Ensure that the input data conforms to the expected Rust types.
  • Cryptography:
    • Serde itself doesn't handle cryptography directly. However, it should be compatible with cryptographic libraries, allowing users to serialize and deserialize encrypted data.
    • If data needs to be signed or encrypted, this should be handled by a separate layer above Serde.
  • Data format specific security:
    • JSON: Avoid features that can lead to vulnerabilities, such as external entity expansion.
    • YAML: Use a safe YAML parser that prevents code execution.
    • Binary formats: Be particularly cautious with binary formats, as they can be more prone to vulnerabilities if not handled carefully.

DESIGN

C4 CONTEXT

graph LR
    subgraph Serde Ecosystem
        User[User Application] --> Serde[Serde Library]
    end
    Serde --> DataFormat[Data Format Library\n(e.g., serde_json, serde_yaml)]
    Serde --> SerializedData[Serialized Data\n(e.g., JSON, YAML, Bincode)]
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Element Descriptions:

  • Element:

    • Name: User Application
    • Type: Software System
    • Description: Any Rust application that uses Serde for serialization and deserialization.
    • Responsibilities: Provides data to be serialized; consumes deserialized data; handles application-specific logic.
    • Security controls: Implements application-level security controls (authentication, authorization, etc.).

  • Element:

    • Name: Serde Library
    • Type: Library
    • Description: The Serde framework itself.
    • Responsibilities: Provides the core serialization and deserialization logic; defines traits and macros for deriving implementations.
    • Security controls: Rust's type safety; avoids unsafe code; extensive testing; fuzz testing.

  • Element:

    • Name: Data Format Library
    • Type: Library
    • Description: Libraries that implement support for specific data formats (e.g., serde_json, serde_yaml).
    • Responsibilities: Handles the parsing and generation of specific data formats.
    • Security controls: Input validation specific to the data format; avoids format-specific vulnerabilities.

  • Element:

    • Name: Serialized Data
    • Type: Data
    • Description: The serialized data in a specific format (e.g., JSON, YAML, Bincode).
    • Responsibilities: Represents the serialized data.
    • Security controls: None directly. Relies on the security of the data format and the application handling the data.

C4 CONTAINER

Since Serde is a library, the container diagram is essentially an extension of the context diagram.

graph LR
    subgraph Serde Ecosystem
        UserApp[User Application] --> SerdeCore[Serde Core]
        UserApp --> SerdeDerive[Serde Derive Macros]
    end
    SerdeCore --> DataFormatImpl[Data Format Implementation\n(e.g., serde_json, serde_yaml)]
    SerdeCore --> SerializedData[Serialized Data\n(e.g., JSON, YAML, Bincode)]
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Element Descriptions:

  • Element:

    • Name: User Application
    • Type: Software System
    • Description: Any Rust application that uses Serde for serialization and deserialization.
    • Responsibilities: Provides data to be serialized; consumes deserialized data; handles application-specific logic.
    • Security controls: Implements application-level security controls (authentication, authorization, etc.).

  • Element:

    • Name: Serde Core
    • Type: Library
    • Description: The core Serde library, containing the Serialize and Deserialize traits and implementations.
    • Responsibilities: Provides the core serialization and deserialization logic.
    • Security controls: Rust's type safety; avoids unsafe code; extensive testing; fuzz testing.

  • Element:

    • Name: Serde Derive Macros
    • Type: Library
    • Description: Procedural macros that automatically generate Serialize and Deserialize implementations for user-defined types.
    • Responsibilities: Simplifies the use of Serde by generating boilerplate code.
    • Security controls: Code generation follows secure coding practices; relies on the security of the core library.

  • Element:

    • Name: Data Format Implementation
    • Type: Library
    • Description: Libraries that implement support for specific data formats (e.g., serde_json, serde_yaml).
    • Responsibilities: Handles the parsing and generation of specific data formats.
    • Security controls: Input validation specific to the data format; avoids format-specific vulnerabilities.

  • Element:

    • Name: Serialized Data
    • Type: Data
    • Description: The serialized data in a specific format (e.g., JSON, YAML, Bincode).
    • Responsibilities: Represents the serialized data.
    • Security controls: None directly. Relies on the security of the data format and the application handling the data.

DEPLOYMENT

Serde is a library, not a standalone application, so it doesn't have a traditional deployment process in the sense of deploying to servers. Instead, it's integrated into other applications. However, we can consider the different ways Serde is "deployed" as a dependency:

Possible Deployment Solutions:

  1. Direct Dependency: The most common way. Applications include Serde as a dependency in their Cargo.toml file. Cargo fetches and builds Serde (and its dependencies) as part of the application's build process.
  2. Vendoring: Copying the source code of Serde (and its dependencies) directly into the application's repository. This gives more control over the exact version used but makes updates more difficult.
  3. Static Linking: Serde is statically linked into the application's binary. This is the default behavior for Rust.
  4. Dynamic Linking (Less Common): Theoretically, Serde could be dynamically linked, but this is less common in Rust.

Chosen Solution (for detailed description): Direct Dependency

graph LR
    Dev[Developer] --> Git[Git Repository]
    Git --> Cargo[Cargo (Build System)]
    Cargo --> Deps[Dependencies\n(crates.io)]
    Deps --> SerdeCrate[Serde Crate]
    Cargo --> AppBinary[Application Binary]
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Element Descriptions:

  • Element:

    • Name: Developer
    • Type: Person
    • Description: The developer writing the application that uses Serde.
    • Responsibilities: Writes code, manages dependencies.
    • Security controls: Follows secure coding practices.

  • Element:

    • Name: Git Repository
    • Type: Repository
    • Description: The application's source code repository.
    • Responsibilities: Stores the application's code, including the Cargo.toml file that specifies dependencies.
    • Security controls: Access control, code review.

  • Element:

    • Name: Cargo (Build System)
    • Type: Tool
    • Description: Rust's build system and package manager.
    • Responsibilities: Fetches dependencies, builds the application.
    • Security controls: Dependency verification (Cargo.lock).

  • Element:

    • Name: Dependencies (crates.io)
    • Type: Repository
    • Description: The central repository for Rust packages (crates).
    • Responsibilities: Hosts Serde and other Rust libraries.
    • Security controls: Package signing (not yet fully implemented in crates.io).

  • Element:

    • Name: Serde Crate
    • Type: Library
    • Description: The Serde library downloaded from crates.io.
    • Responsibilities: Provides serialization and deserialization functionality.
    • Security controls: Relies on the security of crates.io and the Serde codebase.

  • Element:

    • Name: Application Binary
    • Type: Executable
    • Description: The compiled application binary, which includes Serde.
    • Responsibilities: Runs the application logic.
    • Security controls: Relies on the security of the entire build process and the application's code.

BUILD

graph LR
    Dev[Developer] --> Code[Code Changes]
    Code --> PR[Pull Request]
    PR --> CI[CI Server\n(GitHub Actions)]
    CI --> Tests[Run Tests\n(Unit, Integration, Fuzz)]
    CI --> Lint[Run Linters\n(Clippy)]
    CI --> Miri[Run Miri]
    CI --> Artifacts[Build Artifacts\n(crate)]
    Artifacts --> CratesIO[crates.io]
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Build Process Description:

  1. Developer: A developer makes changes to the Serde codebase.
  2. Code Changes: The changes are committed to a local Git repository.
  3. Pull Request: A pull request is created on GitHub to merge the changes into the main branch.
  4. CI Server (GitHub Actions): GitHub Actions, the CI/CD system used by Serde, automatically triggers a build and test pipeline.
  5. Run Tests: The pipeline runs a comprehensive suite of tests, including:
    • Unit tests: Test individual functions and modules.
    • Integration tests: Test the interaction between different parts of Serde.
    • Fuzz tests: Use cargo fuzz to generate random inputs and test for crashes or vulnerabilities.
  6. Run Linters (Clippy): The pipeline runs Clippy to check for common coding mistakes and style issues.
  7. Run Miri: The pipeline runs Miri to check for undefined behavior.
  8. Build Artifacts (crate): If all tests and checks pass, the pipeline builds the Serde crate.
  9. crates.io: The built crate is published to crates.io, the official Rust package registry.

Security Controls in Build Process:

  • security control: Code Review: All changes are reviewed by maintainers before being merged.
  • security control: Automated Testing: Extensive test suite, including fuzz testing, helps catch bugs and vulnerabilities.
  • security control: Linters: Clippy helps enforce coding standards and prevent common mistakes.
  • security control: CI/CD: GitHub Actions automates the build and test process, ensuring consistency and preventing manual errors.
  • security control: Miri: Detects undefined behavior.

RISK ASSESSMENT

Critical Business Processes to Protect:

  • Serialization and Deserialization: The core functionality of Serde must be reliable and secure. Any disruption or vulnerability in these processes can have significant consequences for applications using Serde.
  • Codebase Integrity: Protecting the Serde codebase from unauthorized modification or compromise is crucial, as it's a foundational component of many other projects.

Data to Protect and Sensitivity:

  • Serialized Data (Indirectly): Serde itself doesn't store or manage data directly. However, it handles the representation of data during serialization and deserialization. The sensitivity of this data depends entirely on the application using Serde. It could range from non-sensitive configuration data to highly sensitive personal information or financial data. Serde must ensure that it doesn't introduce vulnerabilities that could expose or corrupt this data.
  • Codebase: The Serde source code itself is a valuable asset. Unauthorized access or modification could introduce vulnerabilities. Sensitivity: High.

QUESTIONS & ASSUMPTIONS

Questions:

  • Are there any specific compliance requirements (e.g., GDPR, HIPAA) that applications using Serde commonly need to adhere to? This would help inform recommendations for data handling.
  • What is the expected threat model for typical applications using Serde? (e.g., web applications, embedded systems, command-line tools). This helps prioritize security controls.
  • What level of performance overhead is acceptable for security measures? This helps determine the feasibility of certain controls (e.g., sandboxing).
  • What are the specific security concerns of the maintainers of Serde?

Assumptions:

  • BUSINESS POSTURE: Assumes that Serde's primary goal is to provide a reliable and efficient serialization/deserialization library for the Rust ecosystem.
  • SECURITY POSTURE: Assumes that Serde maintainers are committed to security best practices and actively address reported vulnerabilities.
  • DESIGN: Assumes that the design of Serde prioritizes memory safety and avoids unnecessary unsafe code.
  • DEPLOYMENT: Assumes that most users will use Serde as a direct dependency via Cargo.
  • BUILD: Assumes that the build process is automated and includes comprehensive testing.