GHSA-j2w3-9c3r-g83q

### Summary

A user who previously had access to a private repository can continue to obtain repository metadata through `GET /api/v1/user/starred` after their access to the repository has been revoked.

After a collaborator is removed from a private repository, direct access to the repository is correctly denied. However, the repository may still appear in the user's starred repository list, and the endpoint continues to return repository metadata. Changes made to that metadata after access revocation are also reflected in subsequent responses.

### Details

The issue affects the authenticated endpoint:

```http GET /api/v1/user/starred ```

The same behavior was also observed on:

```http GET /api/v1/user/subscriptions ```

A reproducible scenario is:

1. User `alice` creates a private repository. 2. User `bob` is granted collaborator access. 3. `bob` stars the repository. 4. `alice` removes `bob` from the repository collaborators. 5. Direct repository access by `bob` is denied. 6. `bob` requests `/api/v1/user/starred`. 7. The repository is still present in the response together with repository metadata.

Additionally, if repository metadata is modified after access revocation, the updated values are returned by `/api/v1/user/starred`.

As a result, a user who no longer has permission to access the repository can continue to obtain repository metadata through the starred repository list.

### PoC

#### PoC Link https://anonymous.4open.science/r/Gitea_PoC-EC93/5_poc_starred_list

#### PoC Details 1. Create a private repository:

```text alice/P description = "INITIAL" ```

2. Add `bob` as a collaborator with read access.

3. As `bob`, star the repository:

```http PUT /api/v1/user/starred/alice/P ```

Response:

```http 204 No Content ```

4. Remove `bob` from the collaborator list.

5. Update the repository description:

```text description = "AFTER-REVOKE" ```

6. Verify that direct repository access is no longer allowed:

```http GET /api/v1/repos/alice/P ```

Response:

```http 404 Not Found ```

7. As `bob`, request the starred repository list:

```http GET /api/v1/user/starred ```

The response still contains the repository entry and reflects the updated description:

```json { "full_name": "alice/P", "description": "AFTER-REVOKE", "private": true } ```

This demonstrates that repository metadata remains accessible through the starred repository list even after repository access has been revoked.

### Impact

A user who previously had legitimate access to a private repository can continue to retrieve repository metadata after losing access to the repository.

The exposed information includes repository metadata returned by the endpoint, such as:

* Repository name (`full_name`) * Repository description * Repository visibility status (`private`)

This issue does not expose repository contents, source code, issues, pull requests, secrets, or collaborator information.

The impact is limited to continued access to repository metadata after repository permissions have been revoked.