experimental_taintUniqueValue
taintUniqueValue
lets you prevent unique values from being passed to Client Components like passwords, keys, or tokens.
taintUniqueValue(errMessage, lifetime, value)
To prevent passing an object containing sensitive data, see taintObjectReference
.
Reference
taintUniqueValue(message, lifetime, value)
Call taintUniqueValue
with a password, token, key or hash to register it with React as something that should not be allowed to be passed to the Client as is:
import {experimental_taintUniqueValue} from 'react';
experimental_taintUniqueValue(
'Do not pass secret keys to the client.',
process,
process.env.SECRET_KEY
);
Parameters
-
message
: The message you want to display ifvalue
is passed to a Client Component. This message will be displayed as a part of the Error that will be thrown ifvalue
is passed to a Client Component. -
lifetime
: Any object that indicates how longvalue
should be tainted.value
will be blocked from being sent to any Client Component while this object still exists. For example, passingglobalThis
blocks the value for the lifetime of an app.lifetime
is typically an object whose properties containsvalue
. -
value
: A string, bigint or TypedArray.value
must be a unique sequence of characters or bytes with high entropy such as a cryptographic token, private key, hash, or a long password.value
will be blocked from being sent to any Client Component.
Returns
experimental_taintUniqueValue
returns undefined
.
Caveats
- Deriving new values from tainted values can compromise tainting protection. New values created by uppercasing tainted values, concatenating tainted string values into a larger string, converting tainted values to base64, substringing tainted values, and other similar transformations are not tainted unless you explicitly call
taintUniqueValue
on these newly created values. - Do not use
taintUniqueValue
to protect low-entropy values such as PIN codes or phone numbers. If any value in a request is controlled by an attacker, they could infer which value is tainted by enumerating all possible values of the secret.
Usage
Prevent a token from being passed to Client Components
To ensure that sensitive information such as passwords, session tokens, or other unique values do not inadvertently get passed to Client Components, the taintUniqueValue
function provides a layer of protection. When a value is tainted, any attempt to pass it to a Client Component will result in an error.
The lifetime
argument defines the duration for which the value remains tainted. For values that should remain tainted indefinitely, objects like globalThis
or process
can serve as the lifetime
argument. These objects have a lifespan that spans the entire duration of your app’s execution.
import {experimental_taintUniqueValue} from 'react';
experimental_taintUniqueValue(
'Do not pass a user password to the client.',
globalThis,
process.env.SECRET_KEY
);
If the tainted value’s lifespan is tied to a object, the lifetime
should be the object that encapsulates the value. This ensures the tainted value remains protected for the lifetime of the encapsulating object.
import {experimental_taintUniqueValue} from 'react';
export async function getUser(id) {
const user = await db`SELECT * FROM users WHERE id = ${id}`;
experimental_taintUniqueValue(
'Do not pass a user session token to the client.',
user,
user.session.token
);
return user;
}
In this example, the user
object serves as the lifetime
argument. If this object gets stored in a global cache or is accessible by another request, the session token remains tainted.
গভীরভাবে জানুন
If you’re running a Server Components environment that has access to private keys or passwords such as database passwords, you have to be careful not to pass that to a Client Component.
export async function Dashboard(props) {
// DO NOT DO THIS
return <Overview password={process.env.API_PASSWORD} />;
}
"use client";
import {useEffect} from '...'
export async function Overview({ password }) {
useEffect(() => {
const headers = { Authorization: password };
fetch(url, { headers }).then(...);
}, [password]);
...
}
This example would leak the secret API token to the client. If this API token can be used to access data this particular user shouldn’t have access to, it could lead to a data breach.
Ideally, secrets like this are abstracted into a single helper file that can only be imported by trusted data utilities on the server. The helper can even be tagged with server-only
to ensure that this file isn’t imported on the client.
import "server-only";
export function fetchAPI(url) {
const headers = { Authorization: process.env.API_PASSWORD };
return fetch(url, { headers });
}
Sometimes mistakes happen during refactoring and not all of your colleagues might know about this. To protect against this mistakes happening down the line we can “taint” the actual password:
import "server-only";
import {experimental_taintUniqueValue} from 'react';
experimental_taintUniqueValue(
'Do not pass the API token password to the client. ' +
'Instead do all fetches on the server.'
process,
process.env.API_PASSWORD
);
Now whenever anyone tries to pass this password to a Client Component, or send the password to a Client Component with a Server Action, an error will be thrown with message you defined when you called taintUniqueValue
.