long Cluster::Parse(long long& pos, long& len) const {
 long status = Load(pos, len);

 if (status < 0)
 return status;

  assert(m_pos >= m_element_start);
  assert(m_timecode >= 0);

 const long long cluster_stop =
 (m_element_size < 0) ? -1 : m_element_start + m_element_size;

 if ((cluster_stop >= 0) && (m_pos >= cluster_stop))
 return 1; // nothing else to do

 IMkvReader* const pReader = m_pSegment->m_pReader;

 long long total, avail;

  status = pReader->Length(&total, &avail);

 if (status < 0) // error
 return status;

  assert((total < 0) || (avail <= total));

  pos = m_pos;

 for (;;) {
 if ((cluster_stop >= 0) && (pos >= cluster_stop))
 break;

 if ((total >= 0) && (pos >= total)) {
 if (m_element_size < 0)
        m_element_size = pos - m_element_start;

 break;
 }


 if ((pos + 1) > avail) {
      len = 1;
 return E_BUFFER_NOT_FULL;
 }

 long long result = GetUIntLength(pReader, pos, len);

 if (result < 0) // error
 return static_cast<long>(result);

 if (result > 0) // weird
 return E_BUFFER_NOT_FULL;

 if ((cluster_stop >= 0) && ((pos + len) > cluster_stop))
 return E_FILE_FORMAT_INVALID;

 if ((pos + len) > avail)
 return E_BUFFER_NOT_FULL;

 const long long id = ReadUInt(pReader, pos, len);

 if (id < 0) // error
 return static_cast<long>(id);

 if (id == 0) // weird
 return E_FILE_FORMAT_INVALID;


 if ((id == 0x0F43B675) || (id == 0x0C53BB6B)) { // Cluster or Cues ID
 if (m_element_size < 0)
        m_element_size = pos - m_element_start;

 break;
 }

    pos += len; // consume ID field


 if ((pos + 1) > avail) {
      len = 1;
 return E_BUFFER_NOT_FULL;
 }

    result = GetUIntLength(pReader, pos, len);

 if (result < 0) // error
 return static_cast<long>(result);

 if (result > 0) // weird
 return E_BUFFER_NOT_FULL;

 if ((cluster_stop >= 0) && ((pos + len) > cluster_stop))
 return E_FILE_FORMAT_INVALID;

 if ((pos + len) > avail)
 return E_BUFFER_NOT_FULL;

 const long long size = ReadUInt(pReader, pos, len);

 if (size < 0) // error
 return static_cast<long>(size);

 const long long unknown_size = (1LL << (7 * len)) - 1;

 if (size == unknown_size)
 return E_FILE_FORMAT_INVALID;

    pos += len; // consume size field

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


 if (size == 0) // weird
 continue;

 const long long block_stop = pos + size;

 if (cluster_stop >= 0) {
 if (block_stop > cluster_stop) {
 if ((id == 0x20) || (id == 0x23))
 return E_FILE_FORMAT_INVALID;

        pos = cluster_stop;
 break;
 }
 } else if ((total >= 0) && (block_stop > total)) {
      m_element_size = total - m_element_start;
      pos = total;
 break;
 } else if (block_stop > avail) {
      len = static_cast<long>(size);
 return E_BUFFER_NOT_FULL;
 }

 Cluster* const this_ = const_cast<Cluster*>(this);

 if (id == 0x20) // BlockGroup
 return this_->ParseBlockGroup(size, pos, len);

 if (id == 0x23) // SimpleBlock
 return this_->ParseSimpleBlock(size, pos, len);

    pos += size; // consume payload
 if (cluster_stop >= 0 && pos > cluster_stop)
 return E_FILE_FORMAT_INVALID;
 }

  assert(m_element_size > 0);

  m_pos = pos;
 if (cluster_stop >= 0 && m_pos > cluster_stop)
 return E_FILE_FORMAT_INVALID;

 if (m_entries_count > 0) {
 const long idx = m_entries_count - 1;

 const BlockEntry* const pLast = m_entries[idx];
    assert(pLast);

 const Block* const pBlock = pLast->GetBlock();
    assert(pBlock);

 const long long start = pBlock->m_start;

 if ((total >= 0) && (start > total))
 return -1; // defend against trucated stream

 const long long size = pBlock->m_size;

 const long long stop = start + size;
    assert((cluster_stop < 0) || (stop <= cluster_stop));

 if ((total >= 0) && (stop > total))
 return -1; // defend against trucated stream
 }

 return 1; // no more entries
}

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.