Characterizing Microarchitectural Side-channel Threats on the Security of Web Browsers
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Kim, Jason
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Abstract
Improving the performance of modern processors faces challenges in frequency, power consumption, and relatively slower memory subsystems. In response, architects have devised complex caching, speculation, and prefetching mechanisms for cutting-edge processors to sidestep such limitations. The resulting products have paved the way for an ecosystem of high-performance web applications, leading to users 'living in the browser' for several hours each day. In turn, these habits have led to web browsers becoming a central store for users' secrets, such as passwords and payment information.
This thesis explores the effect of recent hardware optimizations in processors on the security of web applications rendered by browser engines. Building on the knowledge that some hardware optimizations may backfire for isolation across security domains in the form of microarchitectural side-channels, this thesis discovers optimizations that were previously unseen in production, and demonstrates that both old and new optimizations carry consequences that permeate through the layers of computing abstraction -- all the way to high-stakes application software on top.
The multifaceted attacks that cause the disclosure of users' secrets in this thesis propound that the current landscape of retroactive and incremental side-channel mitigations in web browsers are insufficient to defend against future threats, especially by demonstrating how to undermine several such countermeasures with novel hardware and software primitives. By characterizing the adversarial capabilities of web-based microarchitectural threat actors, this thesis intends to serve as an initial step towards principled defenses for hardening future web browsers.
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Date
2025-12
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Dissertation (PhD)