function bufferCopy(src, dest, srcStart, srcEnd, destStart) {
  if (!destStart)
    destStart = 0;
  if (srcEnd > src.length)
    srcEnd = src.length;
  let nb = srcEnd - srcStart;
  const destLeft = (dest.length - destStart);
  if (nb > destLeft)
    nb = destLeft;
  dest.set(new Uint8Array(src.buffer, src.byteOffset + srcStart, nb),
           destStart);
  return nb;
}
The software constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command when it is sent to a downstream component.