Ech0 is an open-source, self-hosted publishing platform for personal idea sharing. Prior to version 4.2.0, `GET /api/allusers` is mounted as a public endpoint and returns user records without authentication. This allows remote unauthenticated user enumeration and exposure of user profile metadata. A fix is available in v4.2.0.

Affected: Go: github.com/lin-snow/ech0

### Summary A public access-control flaw allows unauthenticated users to retrieve the full user list from `GET /api/allusers`. This exposes user profile metadata to anyone who can reach the application and enables remote user enumeration.

### Details The vulnerable route is registered as a public endpoint:

- `internal/router/user.go:17` - `appRouterGroup.PublicRouterGroup.GET("/allusers", h.UserHandler.GetAllUsers())`

However, the handler appears to have been intended as an authenticated endpoint:

- `internal/handler/user/user.go:177-185` - API annotations indicate an authentication requirement via `@Security ApiKeyAuth`

This creates a mismatch between the documented security model and the actual routing configuration. As a result, requests to `GET /api/allusers` succeed without authentication and return user records, including profile metadata such as usernames, email addresses, role-related flags, avatar values, and locale information.

A negative control against another endpoint that correctly requires authentication further supports that this exposure is unintended: `GET /api/user` returns `401 Unauthorized` when no token is supplied, while `GET /api/allusers` remains publicly accessible.

### Impact - **Type:** Access control bypass / unauthenticated data exposure - **Who is impacted:** Any deployment exposing the API to untrusted networks, and all users whose profile metadata is returned by the endpoint - **Security impact:** Enables remote user enumeration an…