The Pathfinder Attack: A New Threat to Intel CPUs, A Quick look

In the realm of cybersecurity, a new threat has emerged. Researchers have discovered a novel attack method, dubbed ‘Pathfinder’, that targets high-performance Intel CPUs. This attack could potentially be exploited to stage a key recovery attack against the Advanced Encryption Standard (AES) algorithm.

Unveiling the Pathfinder

The Pathfinder attack allows attackers to read and manipulate key components of the branch predictor. This enables two main types of attacks: reconstructing program control flow history and launching high-resolution Spectre attacks. The lead author of the paper, Hosein Yavarzadeh, shared in a statement that this includes extracting secret images from libraries like libjpeg and recovering encryption keys from AES through intermediate value extraction.

The Mechanics of the Attack on Intel CPUs

The latest attack approach targets a feature in the branch predictor called the Path History Register (PHR) – which keeps a record of the last taken branches. This is used to induce branch mispredictions and cause a victim program to execute unintended code paths, thereby inadvertently exposing its confidential data.

The attack introduces new primitives that make it possible to manipulate PHR as well as the prediction history tables (PHTs) within the conditional branch predictor (CBR) to leak historical execution data and ultimately trigger a Spectre-style exploit.

The Impact of the Attack

In a set of demonstrations outlined in the study, the method has been found effective in extracting the secret AES encryption key as well as leaking secret images during processing by the widely used libjpeg image library.

The Response from Intel

Following responsible disclosure in November 2023, Intel, in an advisory released last month, said Pathfinder builds on Spectre v1 attacks and that previously deployed mitigations for Spectre v1 and traditional side-channels mitigate the reported exploits. There is no evidence that it impacts AMD CPUs.

The Implications of the Attack

This research demonstrates that the PHR is vulnerable to leakage, reveals data unavailable through the PHTs, exposes a far greater set of branching code as potential attack surfaces, and cannot be mitigated using techniques proposed for the PHTs.

In conclusion, the Pathfinder attack is a significant development in the field of cybersecurity. It underscores the ongoing challenges in balancing performance optimization with security. As we continue to rely on technology, it is crucial to stay informed and vigilant about potential threats and vulnerabilities.

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