Mobile Network Operators (MNOs) keep a strict control over users accessing the networks by means of the Subscriber Identity Module (SIM). This module grants the user access to the network, by performing the registration and authentication of the user’s device. Without a valid Subscribe IdentityModule (SIM) module and a successful authentication, mobile devices are not granted access and, hence, they are not allowed to inject any traffic in the mobile infrastructure. Nevertheless, in this paper we describe an attack to the security of a mobile network allowing an unauthenticated malicious mobile device to inject traffic in the mobile operator’s infrastructure. We show that even with devices without any SIM module it is possible to inject high levels of signaling traffic in the mobile infrastructure, causing significant service degradation up to a full-fledged Denial of Service (DoS) attack.