1. Introduction
By starting Node.js with the --permission flag, access to resources such as the file system, network, child processes, worker threads, native addons, WASI, and the inspector is restricted.
$ node --permission index.js Error: Access to this API has been restricted
2. Runtime API
When the Permission Model is enabled, the process.permission property is available with the has() method to check permissions:
process.permission.has('fs.write'); // true
process.permission.has('fs.read', '/home/protected'); // false
3. File System Permissions
By default, file system access is restricted. To allow read or write operations, use:
--allow-fs-read=*: Allow all read operations.--allow-fs-write=/tmp/: Allow write access to /tmp.- Supports wildcards:
--allow-fs-read=/home/test*.
4. Using with npx
Enable the Permission Model when running scripts via npx using --node-options:
npx --node-options="--permission" package-name
To avoid FileSystemRead errors, grant read access to global node_modules or npm cache directories.
5. Permission Model Constraints
- Permissions do not inherit to worker threads.
- Restricted features include native modules, network, child processes, file system, WASI, and inspector.
- Certain flags like
--env-fileor--openssl-configbypass the model since they run before initialization. - Existing file descriptors can bypass restrictions.
6. Limitations and Known Issues
- Symbolic links are followed even outside allowed paths.
- Relative symlinks may grant access to arbitrary files and directories.
Conclusion
The Node.js Permission Model is a useful tool for controlling resource access at runtime. While it prevents unintended actions, it does not fully protect against malicious code. Developers must carefully configure allowed paths and be aware of constraints and known issues.