Thwarting Smartphone SMS Attacks at the Radio Interface Layer

—The short message service (SMS) is a cornerstone of modern smartphone communication that enables inter-personal text messaging and other SMS-based services (e.g., two-factor authentication). However, it can also be readily exploited to compromise unsuspecting remote victims. For instance, novel exploits such as Simjacker and WIBAttack enable transmission of binary SMS messages that could surreptitiously execute dangerous commands on a victim device. The SMS channel may also be subverted to drive other nefarious activities (e.g., spamming, DoS, and tracking), thereby undermining end-user security and privacy. Unfortunately, neither contemporary smart- phone operating systems nor existing defense techniques provide a comprehensive bulwark against the spectrum of evolving SMS- driven threats. To address this limitation, we develop a novel defense framework called R IL D EFENDER , which to the best of our knowledge is the first inline prevention system integrated into the radio interface layer (RIL) of Android smartphones. We describe an implementation of R IL D EFENDER on three smartphone models with five Android versions of the Android Open Source Project (AOSP), and show that it is able to protect users from six types of SMS attacks spanning four adversary models. We evaluate R IL D EFENDER against 19 reproduced SMS attacks and 11 contemporary SMS malware samples and find that R IL D EFENDER detects all and automatically prevents all but one of these threats without affecting normal cellular operations.