Memory safety bugs are the most numerous category of Chrome security issues and we’re continuing to investigate many solutions – both in C++ and in new programming languages. The most common type of memory safety bug is the “use-after-free”. We recently posted about an exciting series of technologies designed to prevent these. Those technologies (collectively, *Scan, pronounced “star scan”) are very powerful but likely require hardware support for sufficient performance.
Today we’re going to talk about a different approach to solving the same type of bugs.
It’s hard, if not impossible, to avoid use-after-frees in a non-trivial codebase. It’s rarely a mistake by a single programmer. Instead, one programmer makes reasonable assumptions about how a bit of code will work, then a later change invalidates those assumptions. Suddenly, the data isn’t valid as long as the original programmer expected, and an exploitable bug results.
These bugs have real consequences. For example, according to Google Threat Analysis Group, a use-after-free in the ChromeHTML engine was exploited this year by North Korea.
Half of the known exploitable bugs in Chrome are use-after-frees:
Diving Deeper: Not All Use-After-Free Bugs Are Equal
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