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attack-surface.md

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Attack Surface Analysis for comfyanonymous/comfyui

Attack Surface: 1. Malicious Workflow Execution (Arbitrary Code Execution)

  • Description: Attackers can craft malicious workflow files (JSON) that, when loaded, execute arbitrary code on the ComfyUI server. This is the most significant risk due to ComfyUI's core design.
  • How ComfyUI Contributes: ComfyUI's flexibility in allowing users to define workflows and load them from files, combined with the ability to create custom nodes in Python, creates a direct path for code execution. This is the defining characteristic that makes this attack surface so critical specifically for ComfyUI.
  • Example: An attacker creates a workflow file containing a custom node with a Python script that uses os.system() to execute shell commands, or subprocess.Popen() to spawn a reverse shell. The attacker then convinces a user to load this workflow, or uploads it to a shared ComfyUI instance.
  • Impact: Complete server compromise. The attacker gains full control over the ComfyUI server and potentially the underlying host system. Data theft, data destruction, and lateral movement within the network are all possible.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Workflow Validation: Implement rigorous validation of workflow files before execution. This includes:
      • Schema Validation: Ensure the JSON structure conforms to a predefined schema.
      • Node Type Whitelisting: Only allow known, safe node types. Maintain a whitelist of approved built-in and custom nodes.
      • Parameter Validation: Validate all node parameters (types, ranges, allowed values).
      • Connection Validation: Ensure connections between nodes are valid and do not create unexpected data flows.
    • Sandboxing: Execute custom nodes in a highly restricted environment:
      • Containers: Use Docker or similar containerization technologies to isolate node execution. Limit container resources (CPU, memory, network access).
      • WebAssembly (Wasm): Explore using WebAssembly for custom node execution. Wasm provides a secure, sandboxed environment with limited access to the host system.
      • Restricted Python Environments: If using Python, use techniques like chroot, jailkit, or restricted Python interpreters (e.g., RestrictedPython) to limit the capabilities of the Python code.
    • Digital Signatures: Implement digital signatures for trusted workflows and nodes. Allow users to verify the integrity and origin of workflows before loading them.
    • Safe Mode: Provide a "safe mode" option that disables custom nodes entirely, allowing users to work with only built-in, vetted nodes.
    • User Permissions: Implement user roles and permissions. Restrict the ability to load custom nodes or arbitrary workflows to trusted users.
    • Code Review: Mandatory code review for all custom nodes before they are allowed to be used.

Attack Surface: 2. Denial of Service (Resource Exhaustion)

  • Description: Attackers can create workflows designed to consume excessive server resources (CPU, memory, GPU, disk I/O), leading to a denial of service for legitimate users.
  • How ComfyUI Contributes: ComfyUI's ability to chain together computationally intensive nodes (especially image processing and machine learning operations) and execute them based on user-provided workflows makes it uniquely susceptible to resource exhaustion attacks. The user-defined workflow is the key differentiator.
  • Example: An attacker creates a workflow that repeatedly resizes a very large image to extremely high resolutions, or performs complex image transformations in a loop, consuming all available memory or CPU. Alternatively, a workflow could repeatedly generate and save large images, filling up disk space.
  • Impact: ComfyUI becomes unresponsive, preventing legitimate users from accessing and using the service. Potentially crashes the server.
  • Risk Severity: High
  • Mitigation Strategies:
    • Resource Limits: Implement per-user and per-workflow resource limits:
      • CPU Time Limits: Limit the maximum CPU time a workflow can consume.
      • Memory Limits: Limit the maximum memory a workflow can allocate.
      • GPU Memory Limits: Limit GPU memory usage per workflow.
      • Disk Space Quotas: Limit the amount of disk space a user or workflow can use.
    • Timeouts: Implement timeouts for node execution. If a node takes longer than a specified time to complete, terminate it.
    • Queue Management: Use a queue system to manage workflow execution. Prioritize shorter, less resource-intensive workflows. Implement rate limiting to prevent users from submitting too many workflows in a short period.
    • Monitoring and Alerting: Monitor server resource usage (CPU, memory, GPU, disk I/O). Set up alerts to notify administrators when resource usage exceeds predefined thresholds.

Attack Surface: 3. Vulnerable Custom Nodes (API and Code Injection)

  • Description: Poorly written or malicious custom nodes can introduce vulnerabilities, including command injection, path traversal, and insecure API endpoints.
  • How ComfyUI Contributes: The custom node API is a core ComfyUI feature that allows developers to extend ComfyUI's functionality. This inherent extensibility, while powerful, is the direct source of this attack surface.
  • Example:
    • Command Injection: A custom node takes a user-provided string as input and uses it directly in a shell command without proper sanitization (e.g., os.system("echo " + user_input)).
    • Path Traversal: A custom node allows the user to specify a file path, but does not validate the path, allowing the attacker to access files outside the intended directory (e.g., ../../etc/passwd).
    • Insecure API Endpoint: A custom node exposes a new API endpoint without authentication or authorization, allowing anyone to access and potentially exploit it.
  • Impact: Varies depending on the vulnerability. Could range from data leakage to complete server compromise.
  • Risk Severity: High
  • Mitigation Strategies:
    • Secure Coding Practices: Enforce secure coding guidelines for custom node development. This includes:
      • Input Validation: Thoroughly validate and sanitize all user-provided inputs. Use whitelisting whenever possible.
      • Output Encoding: Properly encode all outputs to prevent cross-site scripting (XSS) vulnerabilities.
      • Avoid Dangerous Functions: Avoid using dangerous functions like os.system(), eval(), exec(), and pickle.loads() without extreme caution and proper sanitization.
    • Sandboxing: (As described in Mitigation for #1 - applies equally here). Isolate custom node execution.
    • API Security:
      • Authentication and Authorization: Implement authentication and authorization for all custom node API endpoints.
      • Rate Limiting: Limit the number of requests to API endpoints to prevent abuse.
      • Input Validation: Validate all API requests and parameters.
    • Code Review: Mandatory code review for all custom nodes.