Fantastic Timers and Where to Find Them: High-Resolution Microarchitectural Attacks in JavaScript

  • Michael SchwarzEmail author
  • Clémentine Maurice
  • Daniel Gruss
  • Stefan Mangard
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 10322)


Research showed that microarchitectural attacks like cache attacks can be performed through websites using JavaScript. These timing attacks allow an adversary to spy on users secrets such as their keystrokes, leveraging fine-grained timers. However, the W3C and browser vendors responded to this significant threat by eliminating fine-grained timers from JavaScript. This renders previous high-resolution microarchitectural attacks non-applicable.

We demonstrate the inefficacy of this mitigation by finding and evaluating a wide range of new sources of timing information. We develop measurement methods that exceed the resolution of official timing sources by 3 to 4 orders of magnitude on all major browsers, and even more on Tor browser. Our timing measurements do not only re-enable previous attacks to their full extent but also allow implementing new attacks. We demonstrate a new DRAM-based covert channel between a website and an unprivileged app in a virtual machine without network hardware. Our results emphasize that quick-fix mitigations can establish a dangerous false sense of security.



We would like to thank our shepherd Jean Paul Degabriele, Georg Koppen from the Tor Browser project as well as all our anonymous reviewers. We would also like to thank the major browser vendors for their quick responses when reporting our findings. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 681402).

Supplementary material


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Copyright information

© International Financial Cryptography Association 2017

Authors and Affiliations

  • Michael Schwarz
    • 1
    Email author
  • Clémentine Maurice
    • 1
  • Daniel Gruss
    • 1
  • Stefan Mangard
    • 1
  1. 1.Graz University of TechnologyGrazAustria

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