Phying News
Curated security research, vulnerabilities, advisories and tools for practitioners.

Trashing the Flow of Data

Summary

In this blog post I want to present crbug.com/944062, a vulnerability in Chrome’s JavaScript compiler TurboFan that was discovered independently by Samuel (saelo@) via fuzzing with fuzzilli, and by myself via manual code auditing. The bug was found in beta and was fixed before it made it into the stable release of Chrome, but I think it’s interesting for a few reasons and decided to write about it. The issue was in TurboFan’s handling of the Array.indexOf builtin and at first it looked like an info leak at best, so it was not clear that you can turn this into an arbitrary write primitive. Besides that, it’s an instance of a common bug pattern in JIT compilers: the code was making assumptions at compile time without inserting the corresponding runtime checks for these assumptions.
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