sec-design-deep-analysis.md

Okay, here's a deep security analysis of mkcert, based on the provided security design review and the project's nature:

1. Objective, Scope, and Methodology

• Objective: To conduct a thorough security analysis of mkcert's key components, identify potential vulnerabilities, assess their impact, and propose actionable mitigation strategies. The analysis will focus on the core functionality of generating and installing locally trusted certificates, considering the business priorities and risks outlined in the security design review. We aim to identify weaknesses that could lead to root CA key compromise, unauthorized certificate issuance, or other security breaches.

• Scope: This analysis covers the following aspects of mkcert:

  • Root CA key generation and storage.
  • Certificate generation process.
  • Trust store installation mechanism.
  • Command-line interface and input validation.
  • Build and deployment processes.
  • Dependency management.
  • Code signing procedures (as described).

  The analysis excludes the security of the underlying operating system, browsers, and the developer's own security practices (beyond how they interact with mkcert). It also excludes a full code audit, focusing instead on architectural and design-level considerations.

• Methodology:

  1. Architecture and Component Inference: Based on the provided C4 diagrams, documentation, and general knowledge of similar tools, we'll infer the likely architecture, components, and data flow within mkcert.
  2. Threat Modeling: For each key component, we'll identify potential threats using a combination of STRIDE (Spoofing, Tampering, Repudiation, Information Disclosure, Denial of Service, Elevation of Privilege) and consideration of the business risks.
  3. Vulnerability Analysis: We'll assess the likelihood and impact of each identified threat, considering existing security controls.
  4. Mitigation Recommendations: We'll propose specific, actionable mitigation strategies tailored to mkcert's design and intended use. These recommendations will prioritize practical steps that align with the project's goal of simplicity.

2. Security Implications of Key Components

We'll break down the security implications of each component, using the C4 Container diagram as a guide:

• 2.1 Command Line Interface (CLI)

  • Threats:
    • Input Validation Bypass: Maliciously crafted command-line arguments could potentially exploit vulnerabilities in argument parsing, leading to unexpected behavior or code execution. (Tampering, Elevation of Privilege)
    • Insecure Defaults: If default settings are insecure (e.g., weak cryptographic parameters), users might unknowingly create vulnerable certificates. (Information Disclosure)
  • Vulnerabilities: Poorly validated domain names (e.g., allowing characters that could lead to command injection in underlying system calls), insufficient checks on file paths, or mishandling of user-supplied configuration.
  • Mitigation:
    • Strict Input Validation: Implement rigorous validation of all command-line arguments, including domain names (using allow-lists and regular expressions that adhere to RFC specifications), file paths, and any other user-supplied data. Reject any input that doesn't conform to expected patterns.
    • Secure Defaults: Ensure that all default settings (e.g., key size, algorithm) are secure by default. Provide clear warnings if the user chooses less secure options.
    • Principle of Least Privilege: Reiterate in documentation that mkcert should be run without elevated privileges whenever possible.

• 2.2 Certificate Generator

  • Threats:
    • Weak Cryptography: Use of weak cryptographic algorithms or insufficient key sizes could allow attackers to forge certificates or break encryption. (Information Disclosure, Tampering)
    • Insecure Random Number Generation: If the random number generator used for key generation is predictable, attackers could potentially recreate the private keys. (Information Disclosure, Spoofing)
    • Code Injection: Vulnerabilities in the certificate generation code could allow attackers to inject malicious data into the generated certificates. (Tampering)
  • Vulnerabilities: Using outdated or deprecated cryptographic libraries, relying on a weak PRNG (Pseudo-Random Number Generator), or failing to properly sanitize data included in the certificate.
  • Mitigation:
    • Strong Cryptography: Use only strong, well-vetted cryptographic algorithms and key sizes. Specifically:
      • RSA: Minimum 2048-bit keys, 4096-bit strongly recommended.
      • ECDSA: Use NIST-approved curves (e.g., P-256, P-384).
      • Signature Algorithm: SHA-256 or stronger.
    • Cryptographically Secure PRNG: Use a cryptographically secure PRNG provided by the Go standard library (crypto/rand). Explicitly verify this is used throughout the codebase.
    • Code Review and Testing: Thoroughly review and test the certificate generation code for potential vulnerabilities, including code injection and buffer overflows. Use static analysis tools.
    • Regular Updates: Keep cryptographic libraries up-to-date to address any newly discovered vulnerabilities.

• 2.3 Trust Store Installer

  • Threats:
    • Incorrect Installation: Failure to correctly install the root CA into the appropriate trust stores could lead to browsers not trusting the generated certificates. (Denial of Service)
    • Privilege Escalation: If mkcert requires elevated privileges to install the CA, a vulnerability in this component could be exploited to gain full system control. (Elevation of Privilege)
    • Tampering with Trust Store: A malicious actor could potentially tamper with the trust store installation process to install their own CA or remove existing trusted CAs. (Tampering)
  • Vulnerabilities: Incorrectly identifying the operating system or browser, using insecure system commands to modify the trust store, or failing to handle errors gracefully.
  • Mitigation:
    • Minimize Privilege Requirements: Design the installation process to require the least possible privileges. If elevated privileges are absolutely necessary, clearly document this and provide warnings. Explore alternative installation methods that don't require full system access.
    • Robust Error Handling: Implement robust error handling to gracefully handle cases where the trust store cannot be modified (e.g., insufficient permissions, unsupported platform). Provide clear error messages to the user.
    • Platform-Specific Security Best Practices: Follow platform-specific security best practices for modifying trust stores. Use well-documented and secure APIs whenever possible. Avoid using shell commands directly if safer alternatives exist.
    • Verification: After installation, verify that the CA was correctly installed and is trusted by the system and browsers. This could involve checking the trust store contents or attempting to connect to a site using a certificate generated by mkcert.

• 2.4 File System

  • Threats:
    • Unauthorized Access to Private Key: If the root CA private key is stored with weak permissions, an attacker could gain access to it. (Information Disclosure)
    • Key Compromise via File System Vulnerabilities: Exploits in the underlying file system could allow attackers to read or modify the private key file. (Information Disclosure, Tampering)
  • Vulnerabilities: Storing the private key in a world-readable location, failing to encrypt the private key at rest, or relying on weak file system permissions.
  • Mitigation:
    • Secure Key Storage:
      • Permissions: Store the root CA private key with the most restrictive permissions possible (e.g., readable and writable only by the user who created it). On Unix-like systems, this would typically be chmod 600.
      • Location: Store the key in a well-defined, secure location (e.g., a dedicated directory within the user's home directory). Clearly document this location.
      • Encryption at Rest (Optional, but Recommended): Consider encrypting the private key at rest using a passphrase provided by the user. This adds an extra layer of protection if the file system is compromised. However, this adds complexity for the user.
    • File System Security: Rely on the underlying operating system's file system security mechanisms to protect the key file. Encourage users to keep their systems up-to-date with security patches.

3. Build and Deployment Processes

• Threats:
  • Supply Chain Attack: Compromise of the GitHub repository, build server, or code signing keys could allow attackers to distribute a malicious version of mkcert. (Tampering)
  • Dependency Vulnerabilities: Vulnerabilities in third-party libraries used by mkcert could be exploited. (Tampering, Elevation of Privilege, etc.)
  • Insecure Build Environment: A compromised build server could inject malicious code into the mkcert binary. (Tampering)
• Vulnerabilities: Weak access controls on the GitHub repository, using outdated or vulnerable dependencies, failing to verify the integrity of downloaded dependencies, or using a compromised build server.
• Mitigation:
  • Secure Code Repository: Use strong access controls and multi-factor authentication for the GitHub repository. Regularly review and audit repository access.
  • Dependency Management:
    • Go Modules: Use Go modules to manage dependencies and ensure that the versions of all dependencies are explicitly specified.
    • Vulnerability Scanning: Regularly scan dependencies for known vulnerabilities using tools like go list -m -u all and govulncheck. Update dependencies promptly to address any identified vulnerabilities.
    • Dependency Pinning: Pin dependencies to specific versions to prevent unexpected changes.
    • Vendor Directory (Optional): Consider using a vendor directory to store copies of dependencies, ensuring that the build process is not affected by external changes.
  • Secure Build Environment: Use a trusted and secure build server (e.g., GitHub Actions). Ensure that the build environment is isolated and that build artifacts are protected from tampering.
  • Code Signing: Continue to code-sign releases to ensure authenticity and integrity. Protect the code signing keys with strong passwords and store them securely. Consider using a hardware security module (HSM) to store the code signing keys.
  • Reproducible Builds (Ideal): Strive for reproducible builds, where the same source code always produces the same binary. This makes it easier to verify that the distributed binary has not been tampered with.

4. Addressing Specific Questions and Assumptions

• Cryptographic Algorithms and Key Sizes: The analysis strongly recommends confirming the specific algorithms and key sizes used. The mitigation section above provides specific recommendations (RSA 2048/4096, ECDSA with NIST curves, SHA-256+).
• Code Signing Process: The details of the code signing process should be documented, including the tools used, key management procedures, and verification steps.
• Trust Store Installation: The platform-specific commands and libraries used for trust store installation should be carefully reviewed for security implications. Avoid using deprecated or insecure methods.
• HSM/Secure Enclave Support: This is a highly recommended enhancement for future versions of mkcert. It would significantly improve the security of the root CA key.
• Certificate Revocation: Implementing a mechanism for revoking certificates is crucial. This could involve creating a simple CRL (Certificate Revocation List) or using a more sophisticated approach. This is a high-priority recommendation.
• Dependency Management: The use of Go modules is a good start, but regular vulnerability scanning and dependency updates are essential.
• Vulnerability Handling Process: A clear process for handling security vulnerabilities should be established and documented. This should include a way for users to report vulnerabilities and a process for disclosing vulnerabilities responsibly.

5. Risk Assessment Summary

The most critical risk is the compromise of the root CA private key. This risk is mitigated by secure key storage practices, but could be further reduced by HSM support. Other significant risks include supply chain attacks and vulnerabilities in dependencies. These risks are mitigated by code signing, dependency management, and secure build practices. The risk of misuse by developers is acknowledged, and mitigation relies primarily on documentation and user education.

6. Actionable Recommendations (Prioritized)

1. High Priority:

   • Verify and Document Cryptography: Confirm and document the exact cryptographic algorithms and key sizes used. Ensure they meet the recommendations outlined above.
   • Implement Certificate Revocation: Develop a mechanism for revoking certificates.
   • Dependency Vulnerability Scanning: Integrate regular dependency vulnerability scanning into the build process.
   • Input Validation: Implement strict input validation for all command-line arguments.
   • Secure Key Storage Documentation: Clearly document the secure key storage practices, including file permissions and recommended location.

2. Medium Priority:

   • HSM/Secure Enclave Support: Investigate and implement support for hardware security modules or secure enclaves.
   • Code Signing Process Documentation: Document the code signing process in detail.
   • Trust Store Installation Review: Review the platform-specific trust store installation mechanisms for security best practices.
   • Vulnerability Handling Process: Establish and document a clear vulnerability handling process.

3. Low Priority:

   • Reproducible Builds: Explore the feasibility of implementing reproducible builds.
   • Encryption at Rest for Private Key: Consider adding an option to encrypt the private key at rest.

This deep analysis provides a comprehensive overview of the security considerations for mkcert. By implementing the recommended mitigation strategies, the development team can significantly enhance the security of the tool and reduce the risk of compromise. Remember that security is an ongoing process, and regular reviews and updates are essential to maintain a strong security posture.