behind-bars — ensure your script is sandboxed

Does it bug you to think that maybe a dependency of a dependency that your script uses, could become malicious and look through your files then phone home anything it wants, as recently seen with crypto wallets in the event-stream attack, or sensitive Linux files? Open source supply chain attacks have been on the rise.

The solution is to run your scripts in a sandboxed environment such as firejail, bubblewrap, or a VM (Docker is a containerization solution, not aimed at security). This module lets you make sure that the sandbox is working as intended. Note that the module doesn't provide sandboxing capabilities itself; use a dedicated tool for that, such as the ones mentioned earlier.

Usage

Simply add import 'behind-bars'; as the first line of your script, and rest assured the script will exit immediately if it can access sensitive files or directories (browser profiles, cryptocurrency wallets, ~/*_history etc.) on Linux/MacOS systems. (PRs welcome for Windows paths)

Config file

You can optionally ensure there's no network access either, or specify custom files/directories to check against, by creating a configuration file behind-bars.json with the following syntax:

{
  "paths": ["~/.conf*"],
  "pathsExtra": ["~/.ssh"],
  "urls": ["https://google.com"]
}

• paths - exit if any of these paths can be read; overrides the default paths
• pathsExtra - check these paths aren't readable in addition to the default ones
• urls - exit if any of these URLs is accessible

Notes:

1. Specify at most one of paths or pathsExtra.
2. The paths* arrays support standard globbing and ~.
3. This configuration file may be a bit awkward compared to exporting a method like ensureNoAccess(), but it's necessary because it's impossible to pass options via ES6 imports, and import statements are hoisted at the top of the script. This means that calling that method would happen after your script had already imported other packages, which could include a malicious dependency that would get a chance to exfiltrate data before ensureNoAccess() runs.

Install

npm i behind-bars

Importing

• TypeScript: import 'behind-bars';
• ES modules .mjs files: import 'behind-bars/index.mjs';
• Old school CommonJS: require('behind-bars/index.js');

This is a hybrid npm package (created using variation 2.4.1 described on that page), with conditional exports that enable named imports even from TypeScript code generating ES Modules, which would otherwise only support default (not named) imports from the CommonJS target of this package (TypeScript doesn't support .mjs input files).

Example

// 'behind-bars' must be the first import
import 'behind-bars';

// ... your code here
// ... imported packages don't have access to sandboxed files

Exit codes

• 1 - one of the checks failed, i.e. the process was able to access a URL or path
• 2 - incorrect usage, e.g. specifying both paths and pathsExtra in the configuration file

Author

Dan Dascalescu

License

MIT