AEX-NStep: Probabilistic Interrupt Counting Attacks on Intel SGX

Nicolas Dutly; Friederike Groschupp; Ivan Puddu; Kari Kostiainen; Srdjan Capkun

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arXiv · 2510.14675

AEX-NStep: Probabilistic Interrupt Counting Attacks on Intel SGX

Nicolas Dutly·Friederike Groschupp·Ivan Puddu·Kari Kostiainen·Srdjan Capkun

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Abstract

To mitigate interrupt-based stepping attacks (notably using SGX-Step), Intel introduced AEX-Notify, an ISA extension to Intel SGX that aims to prevent deterministic single-stepping. In this work, we introduce AEX-NStep, the first interrupt counting attack on AEX-Notify-enabled Enclaves. We show that deterministic single-stepping is not required for interrupt counting attacks to be practical and that, therefore, AEX-Notify does not entirely prevent such attacks. We specifically show that one of AEX-Notify's security guarantees, obfuscated forward progress, does not hold, and we introduce two new probabilistic interrupt counting attacks. We use these attacks to construct a practical ECDSA key leakage attack on an AEX-Notify-enabled SGX enclave. Our results extend the original security analysis of AEX-Notify and inform the design of future mitigations.

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BibTeX RIS

Nicolas Dutly, Friederike Groschupp, Ivan Puddu, Kari Kostiainen, Srdjan Capkun. 2025-10-16. AEX-NStep: Probabilistic Interrupt Counting Attacks on Intel SGX. https://arxiv.org/abs/2510.14675

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