int ff_mms_asf_header_parser(MMSContext *mms)
{
    uint8_t *p = mms->asf_header;
    uint8_t *end;
    int flags, stream_id;
    mms->stream_num = 0;

    if (mms->asf_header_size < sizeof(ff_asf_guid) * 2 + 22 ||
        memcmp(p, ff_asf_header, sizeof(ff_asf_guid))) {
        av_log(NULL, AV_LOG_ERROR,
               "Corrupt stream (invalid ASF header, size=%d)\n",
               mms->asf_header_size);
        return AVERROR_INVALIDDATA;
    }

    end = mms->asf_header + mms->asf_header_size;

    p += sizeof(ff_asf_guid) + 14;
    while(end - p >= sizeof(ff_asf_guid) + 8) {
        uint64_t chunksize;
        if (!memcmp(p, ff_asf_data_header, sizeof(ff_asf_guid))) {
            chunksize = 50; // see Reference [2] section 5.1
        } else {
            chunksize = AV_RL64(p + sizeof(ff_asf_guid));
        }
        if (!chunksize || chunksize > end - p) {
            av_log(NULL, AV_LOG_ERROR,
                   "Corrupt stream (header chunksize %"PRId64" is invalid)\n",
                   chunksize);
            return AVERROR_INVALIDDATA;
        }
        if (!memcmp(p, ff_asf_file_header, sizeof(ff_asf_guid))) {
            /* read packet size */
            if (end - p > sizeof(ff_asf_guid) * 2 + 68) {
                mms->asf_packet_len = AV_RL32(p + sizeof(ff_asf_guid) * 2 + 64);
                if (mms->asf_packet_len <= 0 || mms->asf_packet_len > sizeof(mms->in_buffer)) {
                    av_log(NULL, AV_LOG_ERROR,
                           "Corrupt stream (too large pkt_len %d)\n",
                           mms->asf_packet_len);
                    return AVERROR_INVALIDDATA;
                 }
             }
         } else if (!memcmp(p, ff_asf_stream_header, sizeof(ff_asf_guid))) {
            if (end - p >= (sizeof(ff_asf_guid) * 3 + 26)) {
                flags     = AV_RL16(p + sizeof(ff_asf_guid)*3 + 24);
                stream_id = flags & 0x7F;
                //The second condition is for checking CS_PKT_STREAM_ID_REQUEST packet size,
                //we can calculate the packet size by stream_num.
                //Please see function send_stream_selection_request().
                if (mms->stream_num < MMS_MAX_STREAMS &&
                        46 + mms->stream_num * 6 < sizeof(mms->out_buffer)) {
                    mms->streams = av_fast_realloc(mms->streams,
                                       &mms->nb_streams_allocated,
                                       (mms->stream_num + 1) * sizeof(MMSStream));
                    if (!mms->streams)
                        return AVERROR(ENOMEM);
                    mms->streams[mms->stream_num].id = stream_id;
                    mms->stream_num++;
                } else {
                    av_log(NULL, AV_LOG_ERROR,
                           "Corrupt stream (too many A/V streams)\n");
                    return AVERROR_INVALIDDATA;
                }
             }
         } else if (!memcmp(p, ff_asf_ext_stream_header, sizeof(ff_asf_guid))) {
             if (end - p >= 88) {
                int stream_count = AV_RL16(p + 84), ext_len_count = AV_RL16(p + 86);
                uint64_t skip_bytes = 88;
                while (stream_count--) {
                    if (end - p < skip_bytes + 4) {
                        av_log(NULL, AV_LOG_ERROR,
                               "Corrupt stream (next stream name length is not in the buffer)\n");
                        return AVERROR_INVALIDDATA;
                    }
                    skip_bytes += 4 + AV_RL16(p + skip_bytes + 2);
                }
                while (ext_len_count--) {
                    if (end - p < skip_bytes + 22) {
                        av_log(NULL, AV_LOG_ERROR,
                               "Corrupt stream (next extension system info length is not in the buffer)\n");
                        return AVERROR_INVALIDDATA;
                    }
                    skip_bytes += 22 + AV_RL32(p + skip_bytes + 18);
                }
                if (end - p < skip_bytes) {
                    av_log(NULL, AV_LOG_ERROR,
                           "Corrupt stream (the last extension system info length is invalid)\n");
                    return AVERROR_INVALIDDATA;
                }
                if (chunksize - skip_bytes > 24)
                    chunksize = skip_bytes;
             }
         } else if (!memcmp(p, ff_asf_head1_guid, sizeof(ff_asf_guid))) {
             chunksize = 46; // see references [2] section 3.4. This should be set 46.
            if (chunksize > end - p) {
                av_log(NULL, AV_LOG_ERROR,
                    "Corrupt stream (header chunksize %"PRId64" is invalid)\n",
                    chunksize);
                return AVERROR_INVALIDDATA;
            }
         }
         p += chunksize;
     }

    return 0;
}

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