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

ID SSV:96873
Type seebug
Reporter Root
Modified 2017-11-16T00:00:00


Here's a snippet of the method. void Lowerer::LowerBoundCheck(IR::Instr *const instr) { ... if(rightOpnd->IsIntConstOpnd()) { IntConstType newOffset; if(!IntConstMath::Add(offset, rightOpnd->AsIntConstOpnd()->GetValue(), &newOffset)) <<--- (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;