CVE-2026-44329: free5GC's SMF UPI management interface lacks auth middleware; unauthenticated topology read/write requests reach handlers

free5GC’s SMF mounts the UPI management route group without OAuth2/bearer-token authorization middleware. A network attacker who can reach SMF on the SBI can hit UPI endpoints with no Authorization header at all, and the requests reach the SMF business handlers. In the running Docker lab this was directly demonstrated for read (GET /upi/v1/upNodesLinks), write (POST /upi/v1/upNodesLinks with attacker-controlled UP-node and link payload), and delete (DELETE /upi/v1/upNodesLinks/{nodeID}) operations.

The defect is route-group-scoped: there is no inbound auth middleware on the UPI group at all, while a control comparison against the sibling nsmf-oam group on the same SMF instance shows OAM IS protected (no-token request returns 401 Unauthorized). So this is not a global config gap – it is specifically that the UPI group was mounted without the auth middleware that the OAM group has.