A TOCTOU Attack on DICE Attestation
Stefan Hristozov, Moritz Wettermann, Manuel Huber

TL;DR
This paper reveals a remote TOCTOU attack on DICE-based IoT attestation, showing malware can persist undetected by exploiting runtime vulnerabilities and key theft during firmware execution.
Contribution
It demonstrates a novel TOCTOU attack on DICE attestation in constrained microcontrollers, highlighting security vulnerabilities and discussing potential countermeasures.
Findings
Malware can be installed during runtime without detection.
Attacker can steal attestation keys and reuse them after reboot.
The attack is demonstrated on Cortex-M microcontrollers.
Abstract
A major security challenge for modern Internet of Things (IoT) deployments is to ensure that the devices run legitimate firmware free from malware. This challenge can be addressed through a security primitive called attestation which allows a remote backend to verify the firmware integrity of the devices it manages. In order to accelerate broad attestation adoption in the IoT domain the Trusted Computing Group (TCG) has introduced the Device Identifier Composition Engine (DICE) series of specifications. DICE is a hardware-software architecture for constrained, e.g., microcontroller-based IoT devices where the firmware is divided into successively executed layers. In this paper, we demonstrate a remote Time-Of-Check Time-Of-Use (TOCTOU) attack on DICE-based attestation. We demonstrate that it is possible to install persistent malware in the flash memory of a constrained microcontroller…
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