Black Hat USA 2025 | Conjuring Hardware Failures to Breach CPU Privilege Boundaries

Why It Matters

MCE‑driven attacks bypass traditional interrupt defenses, exposing a new hardware‑rooted privilege‑escalation vector that could compromise even hardened operating systems.

Key Takeaways

• Machine check exceptions cannot be masked or delayed by software.
• Interrupt suppression fails against hardware‑induced machine checks in critical sections.
• Exploiting rare MCEs offers a new privilege‑escalation vector.
• North‑bridge master abort can be induced to trigger MCEs.
• Disabling MCE handling forces CPU reset, limiting mitigation options.

Summary

The Black Hat talk spotlights machine‑check exceptions (MCEs) – hardware‑level fault signals that fire when a CPU detects catastrophic errors such as cache corruption, thermal trips, or external interference. Christopher Domas demonstrates that, unlike ordinary interrupts, MCEs cannot be masked, delayed, or handled in a conventional critical‑section fashion, making them a unique conduit for privilege‑escalation attacks.

He reviews historic exploits – Rafal’s 2012 kernel‑privilege escalation via untimely interrupts, Peterson’s pop‑ss timing trick, and Google Project Zero’s TDX seam‑loader breach – to illustrate how unexpected exceptions can subvert secure transitions. The talk then explains why typical mitigations (IRQ save/restore, flag clearing, NMI masking) fall short: MCEs arrive at the 18th IDT entry and must be serviced immediately, even when all other interrupts are disabled.

Domas proposes a practical trigger: using a PCI master‑abort from the north‑bridge, a controllable hardware condition that forces the CPU to raise an MCE. He walks through the Linux proc‑interrupts view, the layout of machine‑check banks, and the consequences of disabling MCE handling in CR4 – a forced CPU reset. This concrete example shows how an attacker can reliably generate a rare hardware fault to hijack execution.

The implication is clear: hardware‑level fault handling is now an attack surface. Vendors must reconsider default MCE policies, provide finer‑grained reporting, and possibly redesign critical‑path code to be MCE‑aware. Security teams should monitor MCE counters and treat spikes as potential exploitation attempts rather than benign hardware glitches.

Original Description

Catastrophic hardware failures. From an aging I/O device to cosmic ray bit flips, memory degradation to CPU fires. When an unrecoverable hardware error is detected, the common platform response is to generate a Machine Check Exception, and shut down before the problem gets worse.

In this talk, we'll see what happens when we circumvent all the traditional fail safes. What happens when, instead of exceptionally rare failures from natural causes, we deliberately create these fatal events from software. When instead of a platform shutdown, we force the system to limp along, damaged but alive. We'll show how carefully injecting these signals during privileged CPU operations can disrupt secure transitions, how those disruptions progress to cascading system failures, and how to ride the chaos to gain hardware privilege escalation. Finally, we'll see how to undo the damage, recover from the unrecoverable, and let the system continue as if nothing happened - now with a foothold in privileged space, all through hardware failure events synthesized through software-only attacks.

We'll conclude by showing how to use this previously unknown vector against [redacted], to reveal another [redacted] hardware vulnerability, and walk through a brave new world of machine check research opportunities - for both attackers and defenders - across technologies and architectures.

By:

Christopher Domas | Independent Security Researcher, Dazzle Cat Duo

Presentation Materials Available at:

https://blackhat.com/us-25/briefings/schedule/?#ghosts-in-the-machine-check---conjuring-hardware-failures-to-breach-cpu-privilege-boundaries-46846