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attack-surface.md

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Attack Surface Analysis for urfave/cli

Attack Surface: 1. Command/Flag Injection (Unvalidated Input)

  • Description: Attackers inject malicious data into command-line flags or arguments, leading to unintended behavior, often including arbitrary code execution or data manipulation. This is the most direct and dangerous attack vector related to CLI usage.
  • How cli Contributes: urfave/cli provides the mechanism for accepting user input via flags and arguments. It does not automatically validate this input. The framework's purpose is to handle command-line input, making this the core area of concern.
  • Example:
    • A flag --filename=/path/to/file used directly in an os.Remove call: --filename="; rm -rf /"
    • A numeric flag --size=10 used in a memory allocation: --size=999999999999 (leading to a denial-of-service, though this is also resource exhaustion).
    • A flag --query="SELECT * FROM users" used directly in a database query: --query="; DROP TABLE users;"
  • Impact: Arbitrary code execution, data breaches, data loss, denial of service, system compromise.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Developer:
      • Strict Input Validation: Implement rigorous validation for all flag and argument values. Use regular expressions, whitelists, type checks (e.g., strconv for numeric input), and range checks. This is the primary defense.
      • Safe Command Construction: Avoid directly concatenating user input into shell commands or system calls. Use exec.Command with separate arguments, not a single string. Prefer safer alternatives to os/exec when possible.
      • Parameterization: For database interactions, use parameterized queries (prepared statements) to prevent SQL injection.
      • Context-Aware Validation: Use the cli.Context within the Action function to access flag values and perform validation before any potentially dangerous operations.
      • Custom Validators: Utilize the Value field of a Flag to implement custom validation logic.
    • User:
      • Be extremely cautious about the input you provide to CLI applications. Avoid using special characters or potentially dangerous strings unless you are absolutely certain of the application's behavior and have verified its security.

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

  • Description: Attackers provide input to flags designed to consume excessive resources (CPU, memory, disk), making the application unavailable. This leverages the CLI's input mechanism for malicious purposes.
  • How cli Contributes: urfave/cli allows defining flags that can directly control resource allocation (e.g., number of threads, file sizes, buffer sizes). The framework provides the means for the attacker to specify these resource-consuming values.
  • Example:
    • --max-connections=1000000 (attempting to open too many network connections).
    • --buffer-size=10GB (allocating a huge memory buffer).
  • Impact: Application unavailability, service disruption.
  • Risk Severity: High
  • Mitigation Strategies:
    • Developer:
      • Input Limits: Enforce strict limits on flag values that control resource allocation. Use reasonable maximum values, validated using appropriate data types and ranges.
      • Timeouts: Implement timeouts for all potentially slow or blocking operations initiated via CLI commands.
    • User:
      • Avoid providing excessively large values to flags that control resource allocation.

Attack Surface: 3. Hidden/Undocumented Flags

  • Description: Developers include flags not shown in the help output (often for debugging or testing), which attackers might discover and exploit. This is a direct misuse of the CLI framework's features.
  • How cli Contributes: urfave/cli explicitly allows flags to be marked as "hidden," making them invisible in the default help output. This feature, intended for development, creates the vulnerability.
  • Example: A hidden flag --backdoor-access that bypasses authentication.
  • Impact: Unauthorized access, privilege escalation, system compromise.
  • Risk Severity: High
  • Mitigation Strategies:
    • Developer:
      • Remove in Production: Remove or disable hidden flags in production builds. Use build tags or conditional compilation (//go:build !production). This is the most important mitigation.
      • Strong Protection: If absolutely necessary in production (extremely discouraged), protect hidden flags with multiple layers of security (e.g., requiring specific environment variables, configuration file entries, and strong authentication).
    • User: N/A (Users generally cannot mitigate this directly).