long Block::Parse(const Cluster* pCluster) {
 if (pCluster == NULL)
 return -1;

 if (pCluster->m_pSegment == NULL)
 return -1;

  assert(m_start >= 0);
  assert(m_size >= 0);
  assert(m_track <= 0);
  assert(m_frames == NULL);
  assert(m_frame_count <= 0);

 long long pos = m_start;
 const long long stop = m_start + m_size;

 long len;

 IMkvReader* const pReader = pCluster->m_pSegment->m_pReader;

  m_track = ReadUInt(pReader, pos, len);

 if (m_track <= 0)
 return E_FILE_FORMAT_INVALID;

 if ((pos + len) > stop)
 return E_FILE_FORMAT_INVALID;

  pos += len; // consume track number

 if ((stop - pos) < 2)
 return E_FILE_FORMAT_INVALID;

 long status;
 long long value;

  status = UnserializeInt(pReader, pos, 2, value);

 if (status)
 return E_FILE_FORMAT_INVALID;

 if (value < SHRT_MIN)
 return E_FILE_FORMAT_INVALID;

 if (value > SHRT_MAX)
 return E_FILE_FORMAT_INVALID;

  m_timecode = static_cast<short>(value);

  pos += 2;

 if ((stop - pos) <= 0)
 return E_FILE_FORMAT_INVALID;

  status = pReader->Read(pos, 1, &m_flags);

 if (status)
 return E_FILE_FORMAT_INVALID;

 const int lacing = int(m_flags & 0x06) >> 1;

 ++pos; // consume flags byte

 if (lacing == 0) { // no lacing
 if (pos > stop)
 return E_FILE_FORMAT_INVALID;

    m_frame_count = 1;
    m_frames = new (std::nothrow) Frame[m_frame_count];
 if (m_frames == NULL)
 return -1;

 Frame& f = m_frames[0];
    f.pos = pos;

 const long long frame_size = stop - pos;

 if (frame_size > LONG_MAX || frame_size <= 0)
 return E_FILE_FORMAT_INVALID;

    f.len = static_cast<long>(frame_size);

 return 0; // success
 }

 if (pos >= stop)
 return E_FILE_FORMAT_INVALID;

 unsigned char biased_count;

  status = pReader->Read(pos, 1, &biased_count);

 if (status)
 return E_FILE_FORMAT_INVALID;

 ++pos; // consume frame count
 if (pos > stop)
 return E_FILE_FORMAT_INVALID;

  m_frame_count = int(biased_count) + 1;

  m_frames = new (std::nothrow) Frame[m_frame_count];
 if (m_frames == NULL)
 return -1;

 if (!m_frames)
 return E_FILE_FORMAT_INVALID;

 if (lacing == 1) { // Xiph
 Frame* pf = m_frames;
 Frame* const pf_end = pf + m_frame_count;

 long long size = 0;
 int frame_count = m_frame_count;

 while (frame_count > 1) {
 long frame_size = 0;

 for (;;) {
 unsigned char val;

 if (pos >= stop)
 return E_FILE_FORMAT_INVALID;

        status = pReader->Read(pos, 1, &val);

 if (status)
 return E_FILE_FORMAT_INVALID;

 ++pos; // consume xiph size byte

        frame_size += val;

 if (val < 255)
 break;
 }

 Frame& f = *pf++;
      assert(pf < pf_end);
 if (pf >= pf_end)
 return E_FILE_FORMAT_INVALID;

      f.pos = 0; // patch later

 if (frame_size <= 0)
 return E_FILE_FORMAT_INVALID;

      f.len = frame_size;
      size += frame_size; // contribution of this frame

 --frame_count;
 }

 if (pf >= pf_end || pos > stop)
 return E_FILE_FORMAT_INVALID;

 {
 Frame& f = *pf++;

 if (pf != pf_end)
 return E_FILE_FORMAT_INVALID;

      f.pos = 0; // patch later

 const long long total_size = stop - pos;

 if (total_size < size)
 return E_FILE_FORMAT_INVALID;

 const long long frame_size = total_size - size;

 if (frame_size > LONG_MAX || frame_size <= 0)
 return E_FILE_FORMAT_INVALID;

      f.len = static_cast<long>(frame_size);
 }

    pf = m_frames;
 while (pf != pf_end) {
 Frame& f = *pf++;
      assert((pos + f.len) <= stop);

 if ((pos + f.len) > stop)
 return E_FILE_FORMAT_INVALID;

      f.pos = pos;
      pos += f.len;
 }

    assert(pos == stop);
 if (pos != stop)
 return E_FILE_FORMAT_INVALID;

 } else if (lacing == 2) { // fixed-size lacing
 if (pos >= stop)
 return E_FILE_FORMAT_INVALID;

 const long long total_size = stop - pos;

 if ((total_size % m_frame_count) != 0)
 return E_FILE_FORMAT_INVALID;

 const long long frame_size = total_size / m_frame_count;

 if (frame_size > LONG_MAX || frame_size <= 0)
 return E_FILE_FORMAT_INVALID;

 Frame* pf = m_frames;
 Frame* const pf_end = pf + m_frame_count;

 while (pf != pf_end) {
      assert((pos + frame_size) <= stop);
 if ((pos + frame_size) > stop)
 return E_FILE_FORMAT_INVALID;

 Frame& f = *pf++;

      f.pos = pos;
      f.len = static_cast<long>(frame_size);

      pos += frame_size;
 }

    assert(pos == stop);
 if (pos != stop)
 return E_FILE_FORMAT_INVALID;

 } else {
    assert(lacing == 3); // EBML lacing

 if (pos >= stop)
 return E_FILE_FORMAT_INVALID;

 long long size = 0;
 int frame_count = m_frame_count;

 long long frame_size = ReadUInt(pReader, pos, len);

 if (frame_size <= 0)
 return E_FILE_FORMAT_INVALID;

 if (frame_size > LONG_MAX)
 return E_FILE_FORMAT_INVALID;

 if ((pos + len) > stop)
 return E_FILE_FORMAT_INVALID;

    pos += len; // consume length of size of first frame

 if ((pos + frame_size) > stop)
 return E_FILE_FORMAT_INVALID;

 Frame* pf = m_frames;
 Frame* const pf_end = pf + m_frame_count;

 {
 Frame& curr = *pf;

      curr.pos = 0; // patch later

      curr.len = static_cast<long>(frame_size);
      size += curr.len; // contribution of this frame
 }

 --frame_count;

 while (frame_count > 1) {
 if (pos >= stop)
 return E_FILE_FORMAT_INVALID;

      assert(pf < pf_end);
 if (pf >= pf_end)
 return E_FILE_FORMAT_INVALID;


 const Frame& prev = *pf++;
      assert(prev.len == frame_size);
 if (prev.len != frame_size)
 return E_FILE_FORMAT_INVALID;

      assert(pf < pf_end);
 if (pf >= pf_end)
 return E_FILE_FORMAT_INVALID;

 Frame& curr = *pf;

      curr.pos = 0; // patch later

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

 if (delta_size_ < 0)
 return E_FILE_FORMAT_INVALID;

 if ((pos + len) > stop)
 return E_FILE_FORMAT_INVALID;

      pos += len; // consume length of (delta) size
 if (pos > stop)
 return E_FILE_FORMAT_INVALID;

 const int exp = 7 * len - 1;
 const long long bias = (1LL << exp) - 1LL;
 const long long delta_size = delta_size_ - bias;

      frame_size += delta_size;

 if (frame_size <= 0)
 return E_FILE_FORMAT_INVALID;

 if (frame_size > LONG_MAX)
 return E_FILE_FORMAT_INVALID;

      curr.len = static_cast<long>(frame_size);
      size += curr.len; // contribution of this frame

 --frame_count;
 }

 if (frame_count > 0) {
 if (pos > stop || pf >= pf_end)
 return E_FILE_FORMAT_INVALID;

 const Frame& prev = *pf++;
      assert(prev.len == frame_size);
 if (prev.len != frame_size)
 return E_FILE_FORMAT_INVALID;

 if (pf >= pf_end)
 return E_FILE_FORMAT_INVALID;

 Frame& curr = *pf++;
 if (pf != pf_end)
 return E_FILE_FORMAT_INVALID;

      curr.pos = 0; // patch later

 const long long total_size = stop - pos;

 if (total_size < size)
 return E_FILE_FORMAT_INVALID;

      frame_size = total_size - size;

 if (frame_size > LONG_MAX || frame_size <= 0)
 return E_FILE_FORMAT_INVALID;

      curr.len = static_cast<long>(frame_size);
 }

    pf = m_frames;
 while (pf != pf_end) {
 Frame& f = *pf++;
      assert((pos + f.len) <= stop);
 if ((pos + f.len) > stop)
 return E_FILE_FORMAT_INVALID;

      f.pos = pos;
      pos += f.len;
 }

 if (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.