Snipe-IT versions <= 8.6.3 (fixed in 8.7.0) do not validate company assignment authorization before persisting user records via the REST API. In Api\UsersController::store() and ::update(), the user record is filled from the request and saved before the requested company_id / company_ids[] values are filtered against the actor's permitted companies (Company::getIdsForCurrentUser()). On installs using Full Multiple Companies Support (FMCS), a non-superuser holding users.create (or users.edit on a target user) can submit company identifiers for companies outside their scope — including a mix of permitted and foreign ids — causing the account row to be committed to the database before authorization is checked. Where null_company_is_floater=1 is set, the post-hoc filter leaves an empty company pivot and the account is persisted as a "floater" with cross-company visibility, allowing creation or relocation of user accounts across tenant boundaries.