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. Permissions can also control what modules can be accessed by other modules.
- Module-based permissions control which files or URLs are available to other modules during application execution. This can be used to control what modules can be accessed by third-party dependencies, for example.
If you find a potential security vulnerability, please refer to our Security Policy.
Module-based permissions
Policies
自 v11.8.0 版本开始新增
Node.js contains experimental support for creating policies on loading code.
Policies are a security feature intended to allow guarantees about what code Node.js is able to load. The use of policies assumes safe practices for the policy files such as ensuring that policy files cannot be overwritten by the Node.js application by using file permissions.
A best practice would be to ensure that the policy manifest is read-only for the running Node.js application and that the file cannot be changed by the running Node.js application in any way. A typical setup would be to create the policy file as a different user id than the one running Node.js and granting read permissions to the user id running Node.js.
Enabling
The --experimental-policy flag can be used to enable features for policies
when loading modules.
Once this has been set, all modules must conform to a policy manifest file passed to the flag:
BASH
The policy manifest will be used to enforce constraints on code loaded by Node.js.
To mitigate tampering with policy files on disk, an integrity for
the policy file itself may be provided via --policy-integrity.
This allows running node and asserting the policy file contents
even if the file is changed on disk.
BASH
Features
Error behavior
When a policy check fails, Node.js by default will throw an error. It is possible to change the error behavior to one of a few possibilities by defining an "onerror" field in a policy manifest. The following values are available to change the behavior:
"exit": will exit the process immediately. No cleanup code will be allowed to run."log": will log the error at the site of the failure."throw": will throw a JS error at the site of the failure. This is the default.
JSON
Integrity checks
Policy files must use integrity checks with Subresource Integrity strings compatible with the browser integrity attribute associated with absolute URLs.
When using require() or import all resources involved in loading are checked
for integrity if a policy manifest has been specified. If a resource does not
match the integrity listed in the manifest, an error will be thrown.
An example policy file that would allow loading a file checked.js:
JSON
Each resource listed in the policy manifest can be of one the following formats to determine its location:
- A relative-URL string to a resource from the manifest such as
./resource.js,../resource.js, or/resource.js. - A complete URL string to a resource such as
file:///resource.js.
When loading resources the entire URL must match including search parameters
and hash fragment. ./a.js?b will not be used when attempting to load
./a.js and vice versa.
To generate integrity strings, a script such as
node -e 'process.stdout.write("sha256-");process.stdin.pipe(crypto.createHash("sha256").setEncoding("base64")).pipe(process.stdout)' < FILE
can be used.
Integrity can be specified as the boolean value true to accept any
body for the resource which can be useful for local development. It is not
recommended in production since it would allow unexpected alteration of
resources to be considered valid.
Dependency redirection
An application may need to ship patched versions of modules or to prevent modules from allowing all modules access to all other modules. Redirection can be used by intercepting attempts to load the modules wishing to be replaced.
JSON
The dependencies are keyed by the requested specifier string and have values
of either true, null, a string pointing to a module to be resolved,
or a conditions object.
The specifier string does not perform any searching and must match exactly what
is provided to the require() or import except for a canonicalization step.
Therefore, multiple specifiers may be needed in the policy if it uses multiple
different strings to point to the same module (such as excluding the extension).
Specifier strings are canonicalized but not resolved prior to be used for
matching in order to have some compatibility with import maps, for example if a
resource file:///C:/app/server.js was given the following redirection from a
policy located at file:///C:/app/policy.json:
JSON
Any specifier used to load file:///C:/app/utils.js would then be intercepted
and redirected to file:///C:/app/utils-v2.js instead regardless of using an
absolute or relative specifier. However, if a specifier that is not an absolute
or relative URL string is used, it would not be intercepted. So, if an import
such as import('#utils') was used, it would not be intercepted.
If the value of the redirection is true, a "dependencies" field at the top of
the policy file will be used. If that field at the top of the policy file is
true the default node searching algorithms are used to find the module.
If the value of the redirection is a string, it is resolved relative to the manifest and then immediately used without searching.
Any specifier string for which resolution is attempted and that is not listed in the dependencies results in an error according to the policy.
Redirection does not prevent access to APIs through means such as direct access
to require.cache or through module.constructor which allow access to
loading modules. Policy redirection only affects specifiers to require() and
import. Other means, such as to prevent undesired access to APIs through
variables, are necessary to lock down that path of loading modules.
A boolean value of true for the dependencies map can be specified to allow a
module to load any specifier without redirection. This can be useful for local
development and may have some valid usage in production, but should be used
only with care after auditing a module to ensure its behavior is valid.
Similar to "exports" in package.json, dependencies can also be specified to
be objects containing conditions which branch how dependencies are loaded. In
the preceding example, "http" is allowed when the "import" condition is
part of loading it.
A value of null for the resolved value causes the resolution to fail. This
can be used to ensure some kinds of dynamic access are explicitly prevented.
Unknown values for the resolved module location cause failures but are not guaranteed to be forward compatible.
Example: Patched dependency
Redirected dependencies can provide attenuated or modified functionality as fits the application. For example, log data about timing of function durations by wrapping the original:
JS
Scopes
Use the "scopes" field of a manifest to set configuration for many resources
at once. The "scopes" field works by matching resources by their segments.
If a scope or resource includes "cascade": true, unknown specifiers will
be searched for in their containing scope. The containing scope for cascading
is found by recursively reducing the resource URL by removing segments for
special schemes, keeping trailing "/" suffixes, and removing the query and
hash fragment. This leads to the eventual reduction of the URL to its origin.
If the URL is non-special the scope will be located by the URL's origin. If no
scope is found for the origin or in the case of opaque origins, a protocol
string can be used as a scope. If no scope is found for the URL's protocol, a
final empty string "" scope will be used.
Note, blob: URLs adopt their origin from the path they contain, and so a scope
of "blob:https://nodejs.org" will have no effect since no URL can have an
origin of blob:https://nodejs.org; URLs starting with
blob:https://nodejs.org/ will use https://nodejs.org for its origin and
thus https: for its protocol scope. For opaque origin blob: URLs they will
have blob: for their protocol scope since they do not adopt origins.
Example
JSON
Given a file located at file:///C:/app/bin/main.js, the following scopes would
be checked in order:
"file:///C:/app/bin/"
This determines the policy for all file based resources within
"file:///C:/app/bin/". This is not in the "scopes" field of the policy and
would be skipped. Adding this scope to the policy would cause it to be used
prior to the "file:///C:/app/" scope.
"file:///C:/app/"
This determines the policy for all file based resources within
"file:///C:/app/". This is in the "scopes" field of the policy and it would
determine the policy for the resource at file:///C:/app/bin/main.js. If the
scope has "cascade": true, any unsatisfied queries about the resource would
delegate to the next relevant scope for file:///C:/app/bin/main.js, "file:".
"file:///C:/"
This determines the policy for all file based resources within "file:///C:/".
This is not in the "scopes" field of the policy and would be skipped. It would
not be used for file:///C:/app/bin/main.js unless "file:///" is set to
cascade or is not in the "scopes" of the policy.
"file:///"
This determines the policy for all file based resources on the localhost. This
is not in the "scopes" field of the policy and would be skipped. It would not
be used for file:///C:/app/bin/main.js unless "file:///" is set to cascade
or is not in the "scopes" of the policy.
"file:"
This determines the policy for all file based resources. It would not be used
for file:///C:/app/bin/main.js unless "file:///" is set to cascade or is not
in the "scopes" of the policy.
""
This determines the policy for all resources. It would not be used for
file:///C:/app/bin/main.js unless "file:" is set to cascade.
Integrity using scopes
Setting an integrity to true on a scope will set the integrity for any
resource not found in the manifest to true.
Setting an integrity to null on a scope will set the integrity for any
resource not found in the manifest to fail matching.
Not including an integrity is the same as setting the integrity to null.
"cascade" for integrity checks will be ignored if "integrity" is explicitly
set.
The following example allows loading any file:
JSON
Dependency redirection using scopes
The following example, would allow access to fs for all resources within
./app/:
JSON
The following example, would allow access to fs for all data: resources:
JSON
Example: import maps emulation
Given an import map:
JSON
JSON
Import maps assume you can get any resource by default. This means
"dependencies" at the top level of the policy should be set to true.
Policies require this to be opt-in since it enables all resources of the
application cross linkage which doesn't make sense for many scenarios. They also
assume any given scope has access to any scope above its allowed dependencies;
all scopes emulating import maps must set "cascade": true.
Import maps only have a single top level scope for their "imports". So for
emulating "imports" use the "" scope. For emulating "scopes" use the
"scopes" in a similar manner to how "scopes" works in import maps.
Caveats: Policies do not use string matching for various finding of scope. They
do URL traversals. This means things like blob: and data: URLs might not be
entirely interoperable between the two systems. For example import maps can
partially match a data: or blob: URL by partitioning the URL on a /
character, policies intentionally cannot. For blob: URLs import map scopes do
not adopt the origin of the blob: URL.
Additionally, import maps only work on import so it may be desirable to add a
"import" condition to all dependency mappings.