sec-design-deep-analysis.md

Deep Security Analysis of act

1. Objective, Scope, and Methodology

Objective: To conduct a thorough security analysis of act (https://github.com/nektos/act), focusing on its key components, architecture, data flow, and interactions with external systems (primarily Docker and GitHub). The goal is to identify potential security vulnerabilities, assess their impact, and propose actionable mitigation strategies. This analysis will focus on the core functionality of simulating GitHub Actions workflows.

Scope:

• Codebase Analysis: Examining the act source code (Go) to understand its internal workings, including workflow parsing, Docker container management, and interaction with the Docker API.
• Dependency Analysis: Identifying and assessing the security posture of act's dependencies (Go modules, Docker client libraries, base Docker images).
• Workflow Execution: Analyzing how act executes GitHub Actions workflows, including the handling of secrets, environment variables, and user inputs.
• Interaction with External Systems: Evaluating the security implications of act's interactions with Docker Engine and GitHub (repositories, Actions API, etc.).
• Deployment and Build Process: Reviewing the security of the build pipeline and distribution mechanisms.

Methodology:

1. Architecture and Data Flow Inference: Based on the provided design review, codebase, and documentation, we will infer the architecture, components, and data flow of act. This includes identifying key components like the CLI, workflow parser, container manager, and Docker API interactions.
2. Threat Modeling: For each identified component and interaction, we will perform threat modeling using a combination of STRIDE (Spoofing, Tampering, Repudiation, Information Disclosure, Denial of Service, Elevation of Privilege) and attack trees to identify potential threats.
3. Vulnerability Analysis: We will analyze the identified threats to determine their likelihood and impact, considering factors like attack complexity, required privileges, and potential consequences.
4. Mitigation Strategy Recommendation: For each identified vulnerability, we will propose specific, actionable mitigation strategies tailored to act's architecture and implementation. These will go beyond generic recommendations and focus on concrete changes to the code, configuration, or usage of act.

2. Security Implications of Key Components

Based on the C4 diagrams and descriptions, here's a breakdown of the security implications of each key component:

2.1 User (Developer)

• Threats: Compromised developer machine, weak GitHub credentials, malicious workflow files.
• Implications: An attacker with access to the developer's machine could inject malicious code into workflow files, steal credentials, or directly manipulate act. Weak credentials could allow unauthorized access to GitHub repositories.
• Mitigations: This is largely outside the direct control of act. However, act documentation should emphasize the importance of securing the development environment and using strong authentication for GitHub.

2.2 act CLI

• Threats: Command injection, argument injection, denial of service (resource exhaustion).
• Implications: If user-supplied arguments to the act CLI are not properly sanitized, an attacker could inject arbitrary commands to be executed by the host system or Docker. Maliciously crafted input could also cause act to consume excessive resources, leading to a denial of service.
• Mitigations:
  • Strict Input Validation: Implement rigorous input validation and sanitization for all command-line arguments and options. Use a whitelist approach where possible, defining allowed characters and patterns.
  • Avoid Shell Execution: Minimize the use of shell commands and, if necessary, use parameterized commands or libraries that prevent command injection. Prefer direct API calls to Docker over shell-based interactions.
  • Resource Limits: Implement resource limits (CPU, memory, file descriptors) for the act process itself to prevent denial-of-service attacks.

2.3 Workflow Parser

• Threats: YAML parsing vulnerabilities (e.g., billion laughs attack, injection attacks), schema validation bypass, malicious workflow definitions.
• Implications: Vulnerabilities in the YAML parser could allow an attacker to execute arbitrary code, crash the act process, or cause unexpected behavior. Bypassing schema validation could allow for workflows that violate security constraints. A malicious workflow file could contain steps designed to compromise the system.
• Mitigations:
  • Secure YAML Parser: Use a well-vetted, secure YAML parsing library that is known to be resistant to common YAML vulnerabilities. Keep the library up-to-date.
  • Strict Schema Validation: Enforce strict schema validation against the official GitHub Actions workflow schema. Reject any workflow that does not conform to the schema. Regularly update the schema definition.
  • Workflow Sanitization: Even after schema validation, implement additional checks to identify and reject potentially malicious workflow constructs. For example, limit the use of custom scripts or actions from untrusted sources.
  • Regular Expression Review: Carefully review and test any regular expressions used in the parser to avoid ReDoS (Regular Expression Denial of Service) vulnerabilities.

2.4 Container Manager

• Threats: Container escape, privilege escalation, denial of service (resource exhaustion within containers), insecure container configuration.
• Implications: If a container is misconfigured or a vulnerability exists in Docker, an attacker could escape the container and gain access to the host system. Privilege escalation within the container could lead to further compromise. Resource exhaustion within containers could impact the availability of act or other services on the host.
• Mitigations:
  • Least Privilege: Run containers with the minimum necessary privileges. Avoid running containers as root whenever possible. Use Docker's user namespace remapping to map the container's root user to a non-root user on the host.
  • Resource Limits (Docker): Use Docker's resource limits (CPU, memory, disk I/O) to constrain the resources available to each container. This prevents a single compromised container from consuming all available resources.
  • Secure Container Configuration: Follow Docker security best practices when configuring containers. This includes:
    • Using minimal base images.
    • Regularly updating base images.
    • Avoiding unnecessary software in containers.
    • Using read-only file systems where possible.
    • Disabling unnecessary capabilities.
    • Using seccomp profiles to restrict system calls.
    • Using AppArmor or SELinux profiles to enforce mandatory access control.
  • Image Provenance: Verify the source and integrity of Docker images used by act. Use signed images from trusted registries.
  • Network Isolation: Carefully configure network access for containers. Limit network access to only what is strictly necessary. Use Docker networks to isolate containers from each other and from the host network.

2.5 Docker API

• Threats: Man-in-the-middle attacks (if not using TLS), unauthorized access to the Docker daemon.
• Implications: If communication with the Docker API is not secured, an attacker could intercept and modify requests or responses, potentially leading to container compromise. Unauthorized access to the Docker daemon could allow an attacker to control all containers on the system.
• Mitigations:
  • TLS Encryption: Enforce TLS encryption for all communication with the Docker API. Verify the Docker daemon's certificate.
  • Authentication: If the Docker daemon is exposed remotely, require authentication to access the API.
  • Authorization: Implement authorization policies to restrict access to the Docker API based on user roles and permissions. act should only have the minimum necessary permissions.
  • Audit Logging: Enable audit logging for the Docker daemon to track API requests and identify suspicious activity.

2.6 Action Containers

• Threats: Vulnerabilities in base images, malicious code within actions, insecure handling of secrets.
• Implications: Vulnerabilities in the base images used for action containers could be exploited by an attacker. Malicious code within actions could compromise the container and potentially the host system. Insecure handling of secrets could expose sensitive information.
• Mitigations:
  • Base Image Scanning: Regularly scan base images for vulnerabilities using a container image scanning tool (e.g., Trivy, Clair, Anchore). Update base images promptly when vulnerabilities are found.
  • Action Auditing: Encourage users to audit the actions they use, especially those from untrusted sources. Provide guidance on identifying and avoiding malicious actions.
  • Secrets Management: Implement a secure mechanism for handling secrets within act. This could involve:
    • Using environment variables securely (avoiding hardcoding secrets in workflow files).
    • Integrating with a secrets management solution (e.g., HashiCorp Vault, AWS Secrets Manager, Azure Key Vault). This is complex but offers the best security.
    • Providing clear documentation and examples on how to securely pass secrets to actions.
    • Never store secrets directly within the act codebase or configuration.
    • Consider using a temporary, in-memory filesystem for secrets within the container, and ensure it's cleaned up after the action completes.
  • Runtime Monitoring: Consider integrating runtime security monitoring tools to detect and prevent malicious activity within containers.

2.7 Docker Engine

• Threats: Docker daemon vulnerabilities, container escape vulnerabilities, kernel exploits.
• Implications: Vulnerabilities in the Docker daemon or the underlying kernel could allow an attacker to gain complete control of the host system.
• Mitigations:
  • Keep Docker Updated: Regularly update the Docker Engine to the latest stable version to patch known vulnerabilities.
  • Kernel Security: Keep the host operating system's kernel up-to-date and patched.
  • Docker Security Best Practices: Follow Docker's security best practices, including those related to daemon configuration, user namespaces, and resource limits.
  • Consider Rootless Docker: Explore using rootless Docker to run the Docker daemon and containers without root privileges. This significantly reduces the impact of potential vulnerabilities.

2.8 GitHub Actions (Cloud) & GitHub Repository

• Threats: Compromised GitHub account, malicious pull requests, supply chain attacks on GitHub Actions.
• Implications: These are largely outside the control of act but can impact its security. A compromised GitHub account could allow an attacker to modify workflow files or inject malicious code.
• Mitigations: act cannot directly mitigate these threats. Users should follow GitHub's security best practices, including using strong passwords, enabling multi-factor authentication, and carefully reviewing pull requests.

3. Build and Deployment Security

3.1 Build Process

• Threats: Compromised build server, malicious dependencies introduced during the build, unsigned releases.
• Implications: A compromised build server could allow an attacker to inject malicious code into the act binaries. Malicious dependencies could introduce vulnerabilities. Unsigned releases make it difficult to verify the integrity of the downloaded binaries.
• Mitigations:
  • SAST and SCA: Integrate Static Application Security Testing (SAST) and Software Composition Analysis (SCA) tools into the GitHub Actions CI pipeline. Configure these tools to fail the build if vulnerabilities are found above a certain severity threshold. Examples:
    • SAST: GoSec, Snyk Code.
    • SCA: Snyk, Dependabot (built into GitHub), OWASP Dependency-Check.
  • Reproducible Builds: Strive for reproducible builds, where the same source code and build environment always produce the same binary output. This makes it easier to detect tampering.
  • Code Signing: Digitally sign all released act binaries. This allows users to verify the authenticity and integrity of the binaries they download. Use a secure code signing key management system.
  • Build Environment Hardening: Ensure the GitHub Actions runners used for building act are secure. Use minimal base images and keep them up-to-date.

3.2 Deployment (Local Installation - Binary)

• Threats: Man-in-the-middle attacks during download, tampered binaries on GitHub Releases.
• Implications: An attacker could intercept the download of an act binary and replace it with a malicious version. Tampered binaries on GitHub Releases could compromise users who download them.
• Mitigations:
  • HTTPS: Ensure all downloads from GitHub Releases are served over HTTPS.
  • Checksum Verification: Provide checksums (e.g., SHA-256) for all released binaries. Instruct users to verify the checksum of the downloaded binary before executing it. Automate this verification in installation scripts if possible.
  • Code Signing (as mentioned above): Code signing provides a strong guarantee of integrity and authenticity.

4. Risk Assessment and Prioritization

The following table summarizes the key risks, their potential impact, and recommended mitigation priorities:

| Risk | Impact | Likelihood | Priority | Mitigation Strategies

5. Actionable Mitigation Strategies

Based on the analysis above, here are the actionable mitigation strategies, categorized and prioritized:

High Priority (Implement Immediately):

1. Input Validation and Sanitization (CLI & Workflow Parser):

   • Implement strict whitelisting for all user-provided inputs (command-line arguments, workflow file content, environment variables). Define allowed characters, patterns, and data types. Reject any input that doesn't conform.
   • Avoid using shell execution wherever possible. If shell commands are absolutely necessary, use parameterized commands or libraries that prevent command injection (e.g., using exec.Command with separate arguments in Go instead of string concatenation).
   • Use a secure YAML parsing library (like gopkg.in/yaml.v3 or a similar well-vetted library) and ensure it's kept up-to-date. Enable strict mode to prevent known YAML vulnerabilities.
   • Implement strict schema validation against the GitHub Actions workflow schema. Reject any workflow that doesn't conform. Regularly update the schema.
   • Sanitize any user-provided data before using it in Docker commands or file paths.

2. Secure Container Configuration (Container Manager & Docker API):

   • Enforce least privilege for containers. Run containers with non-root users whenever possible. Utilize Docker's user namespace remapping.
   • Set resource limits (CPU, memory, file descriptors, network bandwidth) on all containers to prevent resource exhaustion attacks. Use Docker's built-in resource control features.
   • Use read-only file systems for containers where possible. Mount only necessary volumes with appropriate permissions.
   • Disable unnecessary capabilities within containers using --cap-drop.
   • Use seccomp profiles to restrict the system calls a container can make. Create custom profiles tailored to the specific needs of each action.
   • Use AppArmor or SELinux profiles to enforce mandatory access control within containers.
   • Ensure secure communication with the Docker Engine using TLS. Verify certificates