threat-modeling.md

Threat Model Analysis for nushell/nushell

Threat: Threat 1: Command Injection via run or Direct Execution

• Threat 1: Command Injection via run or Direct Execution

  • Description: An attacker crafts malicious input that is directly incorporated into a NuShell command string executed via the run command or through direct execution of a NuShell script. The attacker might use special characters like semicolons, backticks, pipes, or variable substitutions to inject their own commands. If the application uses user input user_input in a command like run $"ls ($user_input)", an attacker could provide input like "; rm -rf /; #" to execute arbitrary commands.
  • Impact:
    • Complete system compromise.
    • Arbitrary code execution with the privileges of the application.
    • Data exfiltration, modification, or deletion.
    • Denial of service.
  • NuShell Component Affected:
    • run command (and any other command that executes external programs or NuShell scripts).
    • String interpolation and command construction logic within the application.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Primary: Parameterization: Use NuShell's argument passing mechanism to treat user input as data, not code. For example, instead of run $"ls ($user_input)", use run ls $user_input (where $user_input is a NuShell variable containing the user's input). This prevents the input from being interpreted as part of the command itself.
    • Secondary: Strict Input Validation (Whitelist): Implement a very strict whitelist of allowed characters and patterns for user input. Reject any input that doesn't conform to the whitelist. This is a fallback mechanism, not the primary defense. Define exactly what is allowed, not what is forbidden.
    • Avoid run if Possible: If the application's functionality can be achieved using built-in NuShell commands and data manipulation features without resorting to run or external program execution, do so.
    • Least Privilege: Run the NuShell process with the absolute minimum necessary operating system privileges.
    • Sandboxing: Use operating system sandboxing mechanisms (e.g., containers, chroot) to isolate the NuShell process.

Threat: Threat 2: Denial of Service via Resource Exhaustion (Loops, Large Data)

• Threat 2: Denial of Service via Resource Exhaustion (Loops, Large Data)

  • Description: An attacker provides input that causes a NuShell script to enter an infinite loop, consume excessive memory, or perform computationally expensive operations. This could involve large datasets, deeply nested structures, or deliberately crafted input designed to trigger worst-case performance in NuShell's parsing or processing logic.
  • Impact:
    • Application unavailability.
    • System instability due to resource starvation.
  • NuShell Component Affected:
    • NuShell's parser.
    • NuShell's data processing pipeline (various commands, depending on the specific attack).
    • Looping constructs (for, while).
  • Risk Severity: High
  • Mitigation Strategies:
    • Timeouts: Set strict timeouts for NuShell script execution. Terminate any script that exceeds the timeout.
    • Resource Limits (ulimit): Use operating system tools like ulimit (on Linux) or container resource limits to restrict the CPU time, memory, and file descriptors available to the NuShell process.
    • Input Size Limits: Impose strict limits on the size of any input data processed by NuShell.
    • Loop Guards: If using loops, implement safeguards to prevent infinite loops (e.g., maximum iteration counts).
    • Careful Use of Recursive Functions: Avoid or carefully control recursive function calls within NuShell scripts.

Threat: Threat 3: Vulnerability in NuShell Core or Plugins

• Threat 3: Vulnerability in NuShell Core or Plugins

  • Description: A vulnerability exists in the NuShell core engine, a built-in command, or a plugin used by the application. An attacker exploits this vulnerability by providing specially crafted input or interacting with the application in a specific way.
  • Impact:
    • Varies depending on the vulnerability, but could range from denial of service to arbitrary code execution.
  • NuShell Component Affected:
    • Potentially any part of NuShell (core engine, built-in commands, plugins).
  • Risk Severity: High (depending on the specific vulnerability)
  • Mitigation Strategies:
    • Keep NuShell Updated: Regularly update to the latest stable version of NuShell. Monitor NuShell's security advisories and release notes.
    • Plugin Management:
      • Use only trusted plugins from reputable sources.
      • Carefully review the code of any plugins before using them.
      • Keep plugins updated to the latest versions.
      • Consider sandboxing plugins if possible.
    • Vulnerability Scanning: Use vulnerability scanners that can detect known vulnerabilities in NuShell and its dependencies.

Threat: Threat 4: Unintended File System Access

• Threat 4: Unintended File System Access

  • Description: Due to misconfigured file permissions or overly broad access rights, NuShell scripts can read, write, or delete files outside of their intended scope. An attacker might exploit this to access sensitive data or modify critical system files. This is directly related to NuShell because NuShell's commands are the mechanism for file system interaction.
  • Impact:
    • Data exfiltration.
    • Data modification or deletion.
    • System compromise.
  • NuShell Component Affected:
    • Any NuShell command that interacts with the file system (e.g., ls, cp, mv, rm, save, open).
  • Risk Severity: High
  • Mitigation Strategies:
    • Least Privilege (File System): Ensure that the user account running the NuShell process has the absolute minimum necessary file system permissions.
    • Chroot Jail: Run NuShell within a chroot jail to restrict its access to a specific directory subtree.
    • Containerization: Use containers (e.g., Docker) to isolate the NuShell process and its file system access.
    • Regular Permission Audits: Regularly audit file system permissions to identify and correct any overly permissive settings.