Node.js v26.9.0 documentation

Permissions#

Permissions can be used to control what system resources the Node.js process has access to or what actions the process can take with those resources.

• Process-based permissions control the Node.js process's access to resources. The resource can be entirely allowed or denied, or actions related to it can be controlled. For example, file system reads can be allowed while denying writes. This feature does not protect against malicious code. According to the Node.js Security Policy, Node.js trusts any code it is asked to run.

The permission model implements a "seat belt" approach, which prevents trusted code from unintentionally changing files or using resources that access has not explicitly been granted to. It does not provide security guarantees in the presence of malicious code. Malicious code can bypass the permission model and execute arbitrary code without the restrictions imposed by the permission model.

If you find a potential security vulnerability, please refer to our Security Policy.

Process-based permissions#

Permission Model#

The Node.js Permission Model is a mechanism for restricting access to specific resources during execution. The API exists behind a flag --permission which when enabled, will restrict access to all available permissions.

The available permissions are documented by the --permission flag.

The Permission Model has two operational modes:

• Enforce mode (default when using --permission): Access is denied and an ERR_ACCESS_DENIED error is thrown for any operation the process has not been granted permission to perform.
• Audit mode (when using --permission-audit): Permission checks are performed and violations are published through the diagnostics channel, but access is not denied. Execution continues normally. This mode is useful for discovering what permissions your application requires before deploying with enforce mode.

When starting Node.js with --permission, the ability to access the file system through the fs module, access the network, spawn processes, use node:worker_threads, use native addons, use WASI, use FFI, and enable the runtime inspector will be restricted (the listener for SIGUSR1 won't be created).

$ node --permission index.js

Error: Access to this API has been restricted
    at node:internal/main/run_main_module:23:47 {
  code: 'ERR_ACCESS_DENIED',
  permission: 'FileSystemRead',
  resource: '/home/user/index.js'
}
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Allowing access to spawning a process and creating worker threads can be done using the --allow-child-process and --allow-worker respectively.

To allow network access, use --allow-net and for allowing native addons when using permission model, use the --allow-addons flag. For WASI, use the --allow-wasi flag. For FFI, use the --allow-ffi flag. The node:ffi module is only available in builds with FFI support.

To allow use of OpenSSL STORE loaders, for example to load a private key from a <URL> passed to crypto.createPrivateKey(), use the --allow-openssl-store flag. This flag grants broad authority to configured OpenSSL STORE loaders, which may access files, devices, tokens, or the network. Access performed by a loader is not constrained by the fs.read, fs.write, or net permission scopes.

Runtime API#

When enabling the Permission Model through the --permission or --permission-audit flags, a new property permission is added to the process object. This property contains the following functions:

permission.has(scope[, reference])#

API call to check permissions at runtime (permission.has())

process.permission.has('fs.write'); // true
process.permission.has('fs.write', '/home/rafaelgss/protected-folder'); // true

process.permission.has('fs.read'); // true
process.permission.has('fs.read', '/home/rafaelgss/protected-folder'); // false
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permission.drop(scope[, reference])#

API call to drop permissions at runtime. This operation is irreversible.

When called without a reference, the entire scope is dropped. When called with a reference, only the permission for that specific resource is revoked. Dropping a permission only affects future access checks. It does not close or revoke access to resources that are already open, such as file descriptors, network sockets, child processes, or worker threads. Applications are responsible for closing or terminating those resources when they are no longer needed.

You can only drop the exact resource that was explicitly granted. The reference passed to drop() must match the original grant. If a permission was granted using a wildcard (*), only the entire scope can be dropped (by calling drop() without a reference). If a directory was granted (e.g. --allow-fs-read=/my/folder), you cannot drop individual files inside it - you must drop the same directory that was originally granted.

const fs = require('node:fs');

// Read config at startup while we still have permission
const config = fs.readFileSync('/etc/myapp/config.json', 'utf8');

// Drop read access to /etc/myapp after initialization
process.permission.drop('fs.read', '/etc/myapp');

// This will now return false
process.permission.has('fs.read', '/etc/myapp/config.json'); // false

// Drop child process permission entirely
process.permission.drop('child');
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Audit Mode#

The --permission-audit flag enables audit mode for the Permission Model. In audit mode, permission checks are performed but access is not denied — no ERR_ACCESS_DENIED error is thrown. Instead, each permission violation is published through the node:diagnostics_channel module, allowing the application to observe and log which operations would be denied under enforce mode. Execution continues normally.

Audit mode is useful for discovering what permissions your application requires before deploying with --permission. It can also be combined with the --allow-fs-read, --allow-fs-write, --allow-net, --allow-child-process, --allow-worker, --allow-addons, --allow-wasi, and --allow-ffi flags to audit a subset of permissions while granting others.

When a permission check fails in audit mode, a message is published to the diagnostics channel corresponding to the denied scope. The channel names are:

• node:permission-model:fs — File System (read and write)
• node:permission-model:net — Network
• node:permission-model:child — Child Process
• node:permission-model:worker — Worker Threads
• node:permission-model:inspector — Inspector
• node:permission-model:wasi — WASI
• node:permission-model:addon — Native Addons
• node:permission-model:ffi — FFI

Each message is an object with the following properties:

• permission <string> The name of the denied permission scope.
• resource <string> The resource that access was denied to (e.g. a file path or host).

const diagnostics_channel = require('node:diagnostics_channel');

diagnostics_channel.channel('node:permission-model:fs').subscribe((msg) => {
  console.log(`Permission denied: ${msg.permission} on ${msg.resource}`);
});

// Running with --permission-audit, this publishes a diagnostics channel
// message but does not throw
const fs = require('node:fs');
fs.readFileSync('/etc/passwd');
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If both --permission and --permission-audit are specified, --permission takes precedence and the Permission Model runs in enforce mode.

File System Permissions#

The Permission Model, by default, restricts access to the file system through the node:fs module. It does not guarantee that users will not be able to access the file system through other means, such as through the node:sqlite module.

To allow access to the file system, use the --allow-fs-read and --allow-fs-write flags:

$ node --permission --allow-fs-read=* --allow-fs-write=* index.js
Hello world!
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By default the entrypoints of your application are included in the allowed file system read list. For example:

$ node --permission index.js
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• index.js will be included in the allowed file system read list

$ node -r /path/to/custom-require.js --permission index.js
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• /path/to/custom-require.js will be included in the allowed file system read list.
• index.js will be included in the allowed file system read list.

The valid arguments for both flags are:

• * - To allow all FileSystemRead or FileSystemWrite operations, respectively.
• Relative paths to the current working directory.
• Absolute paths.

Example:

• --allow-fs-read=* - It will allow all FileSystemRead operations.
• --allow-fs-write=* - It will allow all FileSystemWrite operations.
• --allow-fs-write=/tmp/ - It will allow FileSystemWrite access to the /tmp/ folder.
• --allow-fs-read=/tmp/ --allow-fs-read=/home/.gitignore - It allows FileSystemRead access to the /tmp/ folder and the /home/.gitignore path.

Wildcards are supported too:

• --allow-fs-read=/home/test* will allow read access to everything that matches the wildcard. e.g: /home/test/file1 or /home/test2

After passing a wildcard character (*) all subsequent characters will be ignored. For example: /home/*.js will work similar to /home/*.

When the permission model is initialized, it will automatically add a wildcard (*) if the specified directory exists. For example, if /home/test/files exists, it will be treated as /home/test/files/*. However, if the directory does not exist, the wildcard will not be added, and access will be limited to /home/test/files. If you want to allow access to a folder that does not exist yet, make sure to explicitly include the wildcard: /my-path/folder-do-not-exist/*.

Some node:fs operations act on an already-open file descriptor rather than a path, so they cannot be tied to a --allow-fs-read or --allow-fs-write grant. When the permission model is enabled these operations are disabled and throw ERR_ACCESS_DENIED, regardless of how the descriptor was obtained. This applies both to the top-level node:fs functions and to the equivalent FileHandle methods, and currently includes fsync/fdatasync, fchmod, and fchown (and their synchronous variants).

Configuration file support#

In addition to passing permission flags on the command line, they can also be declared in a Node.js configuration file when using the experimental [--experimental-config-file][] flag. Permission options must be placed inside the permission top-level object.

Example node.config.json:

{
  "permission": {
    "allow-fs-read": ["./foo"],
    "allow-fs-write": ["./bar"],
    "allow-child-process": true,
    "allow-worker": true,
    "allow-net": true,
    "allow-addons": false,
    "allow-ffi": false,
    "allow-openssl-store": false
  }
}
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When the permission namespace is present in the configuration file, Node.js automatically enables the --permission flag. Run with:

$ node --experimental-default-config-file app.js
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Using the Permission Model with npx#

If you're using npx to execute a Node.js script, you can enable the Permission Model by passing the --node-options flag. For example:

npx --node-options="--permission" package-name
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This sets the NODE_OPTIONS environment variable for all Node.js processes spawned by npx, without affecting the npx process itself.

FileSystemRead Error with npx

The above command will likely throw a FileSystemRead invalid access error because Node.js requires file system read access to locate and execute the package. To avoid this:

1. Using a Globally Installed Package Grant read access to the global node_modules directory by running:

   npx --node-options="--permission --allow-fs-read=$(npm prefix -g)" package-name
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2. Using the npx Cache If you are installing the package temporarily or relying on the npx cache, grant read access to the npm cache directory:

   npx --node-options="--permission --allow-fs-read=$(npm config get cache)" package-name
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Any arguments you would normally pass to node (e.g., --allow-* flags) can also be passed through the --node-options flag. This flexibility makes it easy to configure permissions as needed when using npx.

Permission Model constraints#

There are constraints you need to know before using this system:

• The model does not inherit to a worker thread.
• When using the Permission Model the following features will be restricted:
  • Native modules
  • Network
  • Child process
  • Worker Threads
  • Inspector protocol