long ParseElementHeader(IMkvReader* pReader, long long& pos,
 long long stop, long long& id,
 long long& size) {
 if (stop >= 0 && pos >= stop)
 return E_FILE_FORMAT_INVALID;

 long len;

  id = ReadID(pReader, pos, len);

 if (id < 0)
 return E_FILE_FORMAT_INVALID;

  pos += len; // consume id

 if (stop >= 0 && pos >= stop)
 return E_FILE_FORMAT_INVALID;

  size = ReadUInt(pReader, pos, len);

 if (size < 0 || len < 1 || len > 8) {
 return E_FILE_FORMAT_INVALID;
 }

 const unsigned long long rollover_check =
 static_cast<unsigned long long>(pos) + len;
 if (rollover_check > LONG_LONG_MAX)
 return E_FILE_FORMAT_INVALID;

  pos += len; // consume length of size

 
 
  if (stop >= 0 && pos >= stop)
     return E_FILE_FORMAT_INVALID;
 
   return 0;  // success
}

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.