A Malicious SIM Card Can Run Attacker Code Inside the Modems Behind Cellular IoT Devices

Researchers showed malicious SIM cards can issue RUN AT commands to execute code on Qualcomm modems, compromising Quectel-based cellular IoT devices like EV chargers.

Researchers at the University of Birmingham and Fuzzware found 9 of 26 tested devices accept SIM proactive commands, including six Qualcomm-based cellular modules, five of them Quectel. They achieved code execution on a commercial Autel EV charger via the Quectel EC25's atfwd_daemon unsafe format string, and demonstrated an irreversible 2G downgrade, modem power-off, and arbitrary file reads via a root TFTP daemon on a Quectel EG25-G. Attacks require a hostile SIM already in the slot or an interposer; no attacks have been reported in the wild. Qualcomm has built a hardened configuration disabling the interface by default and Quectel mitigated the file-access flaw; the paper was presented at USENIX WOOT.