GF_Err trex_Read(GF_Box *s, GF_BitStream *bs)
{
	GF_TrackExtendsBox *ptr = (GF_TrackExtendsBox *)s;

	ptr->trackID = gf_bs_read_u32(bs);
	ptr->def_sample_desc_index = gf_bs_read_u32(bs);
	ptr->def_sample_duration = gf_bs_read_u32(bs);
	ptr->def_sample_size = gf_bs_read_u32(bs);
	ptr->def_sample_flags = gf_bs_read_u32(bs);

	if (!ptr->def_sample_desc_index) {
		GF_LOG(GF_LOG_WARNING, GF_LOG_CONTAINER, ("[iso file] TREX with default sample description set to 0, likely broken ! Fixing to 1\n" ));
		ptr->def_sample_desc_index = 1;
	}
	return GF_OK;
}

The product reads data past the end, or before the beginning, of the intended buffer.