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The cellular network offers a ubiquitous emergency call service with its pervasive coverage. In the United States, it can be consumed by dialing 911 for cellular users, and the emergency call is forwarded to the public safety answer point (PSAP), which handles emergency service requests. According to regulatory authority requirements [1,2,3] for cellular emergency services, anonymous user equipment (UE) is allowed to access them without a SIM (Subscriber Identity Module) card, a valid mobile subscription, or a roaming agreement with the visited cellular network. Such support of the cellular emergency services requires different operations from conventional cellular services, thereby increasing the attack surface of the cellular infrastructure.

 

The serine palmitoyltransferase (SPT) complex catalyzes the first and rate-limiting step in sphingolipid biosynthesis in all eukaryotes. ORM/ORMDL proteins are negative regulators of SPT that respond to cellular sphingolipid levels. However, the molecular basis underlying ORM/ORMDL-dependent homeostatic regulation of SPT is not well understood. We determined the cryo–electron microscopy structure ofArabidopsisSPT-ORM1 complex, composed of LCB1, LCB2a, SPTssa, and ORM1, in an inhibited state. A ceramide molecule is sandwiched between ORM1 and LCB2a in the cytosolic membrane leaflet. Ceramide binding is critical for the ORM1-dependent SPT repression, and dihydroceramides and phytoceramides differentially affect this repression. A hybrid β sheet, formed by the amino termini of ORM1 and LCB2a and induced by ceramide binding, stabilizes the amino terminus of ORM1 in an inhibitory conformation. Our findings provide mechanistic insights into sphingolipid homeostatic regulation via the binding of ceramide to the SPT-ORM/ORMDL complex that may have implications for plant-specific processes such as the hypersensitive response for microbial pathogen resistance.

 

More than 150 cellular networks worldwide have rolled out LTE-M (LTE-Machine Type Communication) and/or NB-IoT (Narrow Band Internet of Things) technologies to support massive IoT services such as smart metering and environmental monitoring. Such cellular IoT services share the existing cellular network architecture with non-IoT (e.g., smartphone) ones. When they are newly integrated into the cellular network, new security vulnerabilities may happen from imprudent integration. In this work, we explore the security vulnerabilities of the cellular IoT from both system-integrated and service-integrated aspects. We discover several vulnerabilities spanning cellular standard design defects, network operation slips, and IoT device implementation flaws. Threateningly, they allow an adversary to remotely identify IP addresses and phone numbers assigned to cellular IoT devices, interrupt their power saving services, and launch various attacks, including data/text spamming, battery draining, device hibernation against them. We validate these vulnerabilities over five major cellular IoT carriers in the U.S. and Taiwan using their certified cellular IoT devices. The attack evaluation result shows that the adversary can raise an IoT data bill by up to $226 with less than 120 MB spam traffic, increase an IoT text bill at a rate of $5 per second, and prevent an IoT device from entering/leaving power saving mode; moreover, cellular IoT devices may suffer from denial of IoT services. We finally propose, prototype, and evaluate recommended solutions.