Securing a QNAP NAS

I recently bought a new NAS, after my old one turned ten. I am very satisfied with the reliability of my old QNAP which is still supported with software updates. This makes me a happy customer, and so I did not see any reason to switch brands. After initial setup (networking, firmware update, disabling most services) I did not get around to finishing its setup for a few days. It basically sat there from late May 2020 to early July 2020. Somehow it contracted QSnatch in that timeframe. I’ll explain what I did differently after that.

That NAS is not accessible from the internet, there was no third party software installed, all passwords met very high standards (30 character alphanumeric randomness) and it never had any of the “Stations” (Music, Photo …) activated. It just sat in my home network unused. So while we haven’t seen any media reports of QSnatch since November 2019, this seems to be alive and well somehow. Either, the device came with QSnatch out of the box, or QTS 4.4.2 (probably build 1310 or 1320, all of which are said to be immune until 4.4.3 was released on 2020-07-02) was still vulnerable.

You can probably imagine my surprise when, after the upgrade to QTS 4.4.3 QNAP’s Malware Remover happily reported an infection with MR1905 (QSnatch Malware).

Assessing the situation

So I started over. The NAS is currently not on my network, it’s connected directly to my laptop. I reset the NAS to factory defaults, re-installed QTS 4.4.3 manually by downloading the Firmware to my laptop, checking it for integrity and then uploading it to the NAS by hand. After that I did a nother factory reset. With the NAS still not connected to any networks, I went over every single option available and disabled everything with the exception of SMBv3 Fileserving, SSH and HTTPS for managing the NAS. No Bonjour, no UPnP, no NFS. I didn’t install any additional QNAP software, and I stopped and uninstalled all things that offered the option in the App Center.

So, basically, nothing should be running now. Right?

Wrong. There are still 276 processes running:

[~] # ps -ef        
  PID  Uid     VmSize Stat Command
    1 admin      1888 S   init
    2 admin           SW  [kthreadd]
    3 admin           IW  [kworker/0:0]
    4 admin           IW< [kworker/0:0H]
    7 admin           IWN [mm_percpu_wq]
    8 admin           SW  [ksoftirqd/0]
    9 admin           IW  [rcu_sched]
   10 admin           IW  [rcu_bh]
   11 admin           SW  [migration/0]
   12 admin           SW  [watchdog/0]
   13 admin           SWN [cpuhp/0]
   14 admin           SWN [cpuhp/1]
   15 admin           SW  [watchdog/1]
   16 admin           SW  [migration/1]
   17 admin           SW  [ksoftirqd/1]
   19 admin           IW< [kworker/1:0H]
   20 admin           SWN [cpuhp/2]
   21 admin           SW  [watchdog/2]
   22 admin           SW  [migration/2]
   23 admin           SW  [ksoftirqd/2]
   25 admin           IW< [kworker/2:0H]
   26 admin           SWN [cpuhp/3]
   27 admin           SW  [watchdog/3]
   28 admin           SW  [migration/3]
   29 admin           SW  [ksoftirqd/3]
   31 admin           IW< [kworker/3:0H]
   32 admin           SW  [kdevtmpfs]
   33 admin           IW< [netns]
   38 admin           IW  [kworker/3:1]
   57 admin           IW  [kworker/1:1]
  494 admin           SW  [khungtaskd]
  495 admin           SW  [oom_reaper]
  496 admin           IW< [writeback]
  498 admin           SW  [kcompactd0]
  499 admin           SWN [ksmd]
  500 admin           IW< [crypto]
  501 admin           IW< [kintegrityd]
  502 admin           IW< [kblockd]
  718 admin           IW< [tifm]
  724 admin           IW< [ata_sff]
  742 admin           IW< [md]
  759 admin           IW< [watchdogd]
  862 admin           IW< [rpciod]
  863 admin           IW< [xprtiod]
  886 admin           SW  [kauditd]
  895 admin           SW  [kswapd0]
  897 admin           SW  [ecryptfs-kthrea]
  899 admin           IW< [nfsiod]
  900 admin           IW< [cifsiod]
  901 admin           IW< [cifsoplockd]
  945 admin           IW< [kthrotld]
 1552 admin           IW< [knbd-recv]
 1589 admin           IW< [kmpath_rdacd]
 1596 admin           IW< [nvme-wq]
 1607 admin           SW  [scsi_eh_0]
 1608 admin           IW< [scsi_tmf_0]
 1611 admin           SW  [scsi_eh_1]
 1612 admin           IW< [scsi_tmf_1]
 1653 admin           SW  [scsi_eh_2]
 1654 admin           IW< [scsi_tmf_2]
 1657 admin           SW  [scsi_eh_3]
 1658 admin           IW< [scsi_tmf_3]
 1661 admin           SW  [scsi_eh_4]
 1662 admin           IW< [scsi_tmf_4]
 1665 admin           SW  [scsi_eh_5]
 1666 admin           IW< [scsi_tmf_5]
 1669 admin           SW  [scsi_eh_6]
 1670 admin           IW< [scsi_tmf_6]
 1673 admin           SW  [scsi_eh_7]
 1674 admin           IW< [scsi_tmf_7]
 1677 admin           SW  [scsi_eh_8]
 1678 admin           IW< [scsi_tmf_8]
 1681 admin           SW  [scsi_eh_9]
 1682 admin           IW< [scsi_tmf_9]
 1685 admin           SW  [scsi_eh_10]
 1686 admin           IW< [scsi_tmf_10]
 1689 admin           SW  [scsi_eh_11]
 1690 admin           IW< [scsi_tmf_11]
 1693 admin           SW  [scsi_eh_12]
 1694 admin           IW< [scsi_tmf_12]
 1697 admin           SW  [scsi_eh_13]
 1698 admin           IW< [scsi_tmf_13]
 1732 admin           IW  [kworker/u8:8]
 1734 admin           RW  [kworker/u8:10]
 1780 admin           SW  [rc0]
 1787 admin           IW< [raid5wq]
 1789 admin           IW< [dm-block-clone]
 1791 admin           IW< [dm_bufio_cache]
 1792 admin           IW< [kmpathd]
 1793 admin           IW< [kmpath_handlerd]
 1797 admin           SW  [irq/3-mmc0]
 1801 admin           SW  [irq/130-0000:00]
 1803 admin           IW  [kworker/2:2]
 1804 admin           SW  [irq/39-mmc1]
 1855 admin           SW  [i915/signal:0]
 1856 admin           SW  [i915/signal:1]
 1857 admin           SW  [i915/signal:2]
 1858 admin           SW  [i915/signal:4]
 1943 admin           SW  [mmcqd/1]
 1944 admin           SW  [mmcqd/1boot0]
 1945 admin           SW  [mmcqd/1boot1]
 1946 admin           SW  [mmcqd/1rpmb]
 1963 admin           IW  [kworker/0:1]
 1966 admin           IW< [kworker/2:1H]
 1967 admin           IW< [kworker/1:1H]
 2253 admin           IW< [bioset]
 2254 admin           IW< [kcopyd]
 2255 admin           IW< [bioset]
 2256 admin           IW< [kcopyd_tracked]
 2257 admin           IW< [bioset]
 2266 admin           IW< [drbd-reissue]
 2286 admin           IW< [kworker/0:1H]
 2366 admin      1708 S < udevd --daemon
 2409 admin           IW< [kworker/3:1H]
 2479 admin           SW  [md9_raid1]
 2492 admin           SW  [jbd2/md9-8]
 2493 admin           IW< [ext4-rsv-conver]
 2506 admin           SW  [md13_raid1]
 2642 admin     10796 S   /sbin/hal_daemon -f
 2714 admin           SW  [md256_raid1]
 2736 admin           SW  [md322_raid1]
 2774 admin           SW  [md1_raid5]
 2789 admin           IW  [kworker/3:2]
 2815 admin           IW< [drbd1_submit]
 2823 admin           SW  [drbd_w_r1]
 2938 admin           IW< [kdmflush]
 2941 admin           IW< [bioset]
 2945 admin           IW< [kdmflush]
 2947 admin           IW< [bioset]
 2952 admin           IW< [kdmflush]
 2954 admin           IW< [bioset]
 2957 admin           IW< [kdmflush]
 2959 admin           IW< [bioset]
 2962 admin           IW< [kdmflush]
 2978 admin           IW< [bioset]
 2986 admin           IW< [kdmflush]
 2988 admin           IW< [bioset]
 2989 admin           IW< [kcopyd]
 2990 admin           IW< [bioset]
 2991 admin           IW< [dm-thin]
 2992 admin           IW< [dm-thin-paralle]
 2993 admin           IW< [dm-tier]
 2994 admin           IW< [dm-tier]
 2995 admin           IW< [dm-tier]
 2996 admin           IW< [dm-tier]
 2997 admin           IW< [dm-tier-discard]
 2998 admin           IW< [kcopyd]
 2999 admin           IW< [bioset]
 3000 admin           IW< [dm-tier-cache-t]
 3001 admin           IW< [bioset]
 3006 admin           IW< [kdmflush]
 3008 admin           IW< [bioset]
 3014 admin           IW< [kdmflush]
 3017 admin           IW< [bioset]
 3359 admin           IW< [kdmflush]
 3361 admin           IW< [bioset]
 3504 admin           IW< [vfio-irqfd-clea]
 3529 admin       684 S   /sbin/lvmetad
 3624 admin           SWN [kcp_p]
 3625 admin           DWN [kcp_c]
 3748 admin           IW  [kworker/1:2]
 3749 admin           SW  [jbd2/md13-8]
 3750 admin           IW< [ext4-rsv-conver]
 4258 admin           SW  [notify thread]
 4266 admin       740 S < qWatchdogd: keeping alive every 5 seconds...
 4356 admin           IW< [ipv6_addrconf]
 4479 admin      1472 S   /sbin/netwatchdog -d
 4511 admin      4164 S   /sbin/cs_daemon
 4524 admin      4956 S   /sbin/cs_qdaemon
 4782 admin       856 S   /sbin/modagent
 5542 admin       704 S   /usr/local/network/bin/logrotate /var/log/network/err.log 102400
 5544 admin      1152 S   tail -f /var/log/network/err_log
 5545 admin       700 S   /usr/local/network/bin/logrotate /var/log/network/events.log 102400
 5548 admin      1008 S   tail -f /var/log/network/events_log
 5870 admin     22148 S   /mnt/ext/opt/Python/bin/python ./manage.pyc runfcgi method=threaded socket=/tmp/netmgr.sock pidfile=/tmp/netmgr.pid
 5910 admin      3400 S   /mnt/ext/opt/netmgr/util/redis/redis-server *:0
 5920 admin     28712 S   /mnt/ext/opt/Python/bin/python /mnt/ext/opt/netmgr/api/core/asd.pyc
 6578 admin           IW< [bond0]
 6581 admin           IW< [bond1]
 7490 admin       104 S   /sbin/rdnssd -r /var/lib/rdnssd/ -p /var/run/network/rdnssd.pid -u admin
 7491 admin      1624 S   /sbin/rdnssd -r /var/lib/rdnssd/ -p /var/run/network/rdnssd.pid -u admin
 7503 admin      7248 S   /usr/local/bin/ifd
 7616 admin      7876 S   /usr/sbin/dhclient -6 -nw -S -cf /etc/dhcp/dh6dns.conf -lf /dev/null -e FPATH=/var/lib/dh6dns -sf /sbin/dh6dns-script -pf /var/lib/dh6dns/eth0.pid eth0
 7638 admin     21856 S   python /usr/local/network/nmd/nmd.pyc
 7643 admin     15964 S   python /usr/local/network/nmd/nmd.pyc
 7644 admin     18192 S   python /usr/local/network/nmd/nmd.pyc
 7997 admin     18416 S   python /usr/local/network/nmd/nmd.pyc
 7998 admin     18920 S   python /usr/local/network/nmd/nmd.pyc
 7999 admin     18080 S   python /usr/local/network/nmd/nmd.pyc
 8001 admin     15696 S   python /usr/local/network/nmd/nmd.pyc
 8002 admin     17312 S   python /usr/local/network/nmd/nmd.pyc
 8003 admin     17220 S   python /usr/local/network/nmd/nmd.pyc
 8008 admin     15256 S   python /usr/local/network/nmd/nmd.pyc
 8010 admin     15200 S   python /usr/local/network/nmd/nmd.pyc
 8012 admin     18388 S   python /usr/local/network/nmd/nmd.pyc
 8014 admin      2888 S   /usr/local/bin/rates_monitor_start
 8025 admin     22020 S   /mnt/ext/opt/Python/bin/python /mnt/ext/opt/netmgr/api/core/ip_monitor.pyc
 8426 admin      1896 S   /sbin/dnsmasq
 9063 admin           IW< [iscsi_eh]
 9092 admin           SW  [qnap_et]
 9121 admin      1428 S   /sbin/iscsid --config=/etc/config/iscsi/sbin/iscsid.conf --initiatorname=/etc/iscsi/initiatorname.iscsi
 9122 admin      2720 S < /sbin/iscsid --config=/etc/config/iscsi/sbin/iscsid.conf --initiatorname=/etc/iscsi/initiatorname.iscsi
 9134 admin      6248 S   /sbin/vdd_control -d
 9329 admin      9596 S   /sbin/qpkgd -d0
 9860 admin      4284 S   /usr/local/bin/ql_daemon -d 7
10413 admin     29080 S   /usr/local/sbin/ncdb --defaults-file=/mnt/ext/opt/NotificationCenter/etc/nc-mariadb.conf
10444 admin      1964 S   /usr/local/sbin/ncloud
10458 admin     12924 S   /usr/local/sbin/ncd
11236 guest      2416 S   /usr/sbin/dbus-daemon --system
11728 admin      4932 S   /usr/local/sbin/Qthttpd -p 80 -nor -nos -u admin -d /home/Qhttpd -c **.*
11777 admin      3248 S   /usr/sbin/cupsd -C /etc/config/cups/cupsd.conf -s /etc/config/cups/cups-files.conf
12105 admin      7992 S < /usr/local/samba/sbin/winbindd -s /etc/config/smb.conf
12288 admin     12848 S   /usr/local/samba/sbin/smbd -l /var/log -D -s /etc/config/smb.conf
12291 admin      6012 S   /usr/local/samba/sbin/smbd -l /var/log -D -s /etc/config/smb.conf
12293 admin      6012 S   /usr/local/samba/sbin/smbd -l /var/log -D -s /etc/config/smb.conf
12298 admin     13372 S < /usr/local/samba/sbin/winbindd -s /etc/config/smb.conf
12299 admin      3772 S < /usr/local/samba/sbin/winbindd -s /etc/config/smb.conf
12300 admin      6324 S < /usr/local/samba/sbin/winbindd -s /etc/config/smb.conf
12301 admin      7792 S   /usr/local/samba/sbin/smbd -l /var/log -D -s /etc/config/smb.conf
12302 admin      7868 S   /usr/local/samba/sbin/smbd -l /var/log -D -s /etc/config/smb.conf
12303 admin      6980 S   /usr/local/samba/sbin/smbd -l /var/log -D -s /etc/config/smb.conf
12304 admin      6976 S   /usr/local/samba/sbin/smbd -l /var/log -D -s /etc/config/smb.conf
12305 admin      6984 S   /usr/local/samba/sbin/smbd -l /var/log -D -s /etc/config/smb.conf
12306 admin      6984 S   /usr/local/samba/sbin/smbd -l /var/log -D -s /etc/config/smb.conf
12307 admin      6984 S   /usr/local/samba/sbin/smbd -l /var/log -D -s /etc/config/smb.conf
12356 admin      5680 S   /usr/local/samba/sbin/nmbd -l /var/log -D -s /etc/config/smb.conf
12445 admin     14848 S   /mnt/ext/opt/Python/bin/python2 /sbin/wsd.py
12637 admin      5280 S   /usr/local/sbin/_thttpd_ -p 58080 -nor -nos -u admin -d /home/httpd -c **.* -h 127.0.0.1 -i /var/lock/._thttpd_.pid
12646 admin      4360 S   /usr/bin/qooba --service spotlight
12689 admin     10820 S   php-fpm: master process (/etc/php-fpm-sys-proxy.conf)
12690 admin      7296 S   php-fpm: pool www
12691 admin      7296 S   php-fpm: pool www
12793 admin      7692 S < /usr/local/apache/bin/apache_proxy -k start -f /etc/apache-sys-proxy.conf
13449 admin      3780 S   /usr/sbin/ntpdated
13496 admin      6968 S   /usr/sbin/upsutil
13523 admin           IW  [kworker/u8:0]
13564 admin      2000 S   /usr/sbin/crond -l 9 -c /tmp/cron/crontabs
13567 admin     10332 S   /usr/local/apache/bin/apache_proxys -k start -f /etc/apache-sys-proxy-ssl.conf
13921 admin      4028 S   /usr/sbin/sshd -f /etc/config/ssh/sshd_config -p 22
14151 admin      3896 S   /usr/bin/lunportman
14224 admin      2252 S   /sbin/rfsd -i -f /etc/rfsd.conf
14238 admin      4608 S   /usr/local/bin/rfsd_qmonitor -f:/tmp/rfsd_qmonitor.conf
14495 admin     14996 S   /sbin/bcclient
14757 admin      1556 S N /sbin/acpid
14788 admin      3164 S   /usr/sbin/rsyslogd -f /etc/rsyslog_only_klog.conf -c4 -M /usr/local/lib/rsyslog/
14831 admin           IW  [kworker/2:1]
14912 admin      2480 S   /sbin/gen_bandwidth -r -i 5
15244 admin      4556 S   qNoticeEngined: Write notice is enabled...
15256 admin      4916 S   /sbin/qsyslogd
15273 admin      5324 S   /sbin/qShield
15277 admin      6308 S   qLogEngined: Write log is disabled...
15426 admin      2660 S   /bin/sh /etc/rcS.d/S99cloudinstall_report_complete_daemon start
15531 admin      7764 S   /usr/bin/qstorman
15553 admin      5196 S   /sbin/sdmd --daemon
15581 admin      7524 S   /usr/bin/qsnapman
16868 admin      8160 S   /usr/bin/qsnapman-alive
17842 admin      1000 S   sleep 86400
17881 admin      7672 S   /usr/bin/qsnapman-smart
18152 admin      8828 S   /usr/bin/qsnapman-recyc
18453 admin       964 S   /bin/sleep 1
18491 admin      8256 R   /usr/local/bin/python /usr/local/network/ni_utils/API.pyc cu Check_access_internet ["eth0"]
18493 admin      5292 S   qmonitor -pid:99999999 -client:test -reg:/qqqqqqqqqqqqqqqq -filter:0x7fff
18494 admin      2380 R   ps -ef
19789 admin      4880 S   /sbin/daemon_mgr
19813 admin      2044 S   /usr/share/qnas_console_install/drawPic
20614 admin      4116 S < /usr/local/apache/bin/fcgi-pm      -k start -f /etc/apache-sys-proxy.conf
20619 admin     11644 S < /usr/local/apache/bin/apache_proxy -k start -f /etc/apache-sys-proxy.conf
20838 admin      4468 S   /usr/local/apache/bin/fcgi-pm       -k start -f /etc/apache-sys-proxy-ssl.conf
20841 admin     15108 S   /usr/local/apache/bin/apache_proxys -k start -f /etc/apache-sys-proxy-ssl.conf
22802 admin      3488 S   /bin/sh /sbin/qdesk_soldier
23575 admin      7760 S   /sbin/upnpcd -i 300
23938 admin      1952 S   /sbin/getty 115200 tty1
23939 admin      1952 S   /sbin/getty 115200 tty2
23943 admin      1832 S   /sbin/getty -L ttyS0 115200 vt100
27380 admin      8592 R   sshd: admin@pts/0
27387 admin      3772 S   -sh

And a lot of ports are open, too:

[~] # netstat -tulpn 
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 0.0.0.0:139             0.0.0.0:*               LISTEN      12288/smbd
tcp        0      0 127.0.1.1:53            0.0.0.0:*               LISTEN      8426/dnsmasq
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      13921/sshd
tcp        0      0 0.0.0.0:631             0.0.0.0:*               LISTEN      11777/cupsd
tcp        0      0 0.0.0.0:445             0.0.0.0:*               LISTEN      12288/smbd
tcp        0      0 127.0.0.1:58080         0.0.0.0:*               LISTEN      12637/_thttpd_
tcp        0      0 :::139                  :::*                    LISTEN      12288/smbd
tcp        0      0 :::8080                 :::*                    LISTEN      12793/apache_proxy
tcp        0      0 :::80                   :::*                    LISTEN      11728/Qthttpd
tcp        0      0 :::22                   :::*                    LISTEN      13921/sshd
tcp        0      0 :::631                  :::*                    LISTEN      11777/cupsd
tcp        0      0 :::443                  :::*                    LISTEN      13567/apache_proxys
tcp        0      0 :::445                  :::*                    LISTEN      12288/smbd
udp        0      0 0.0.0.0:35255           0.0.0.0:*                           12445/python2
udp        0      0 0.0.0.0:59927           0.0.0.0:*                           8426/dnsmasq
udp        0      0 0.0.0.0:3702            0.0.0.0:*                           12445/python2
udp        0      0 255.255.255.255:8097    0.0.0.0:*                           14495/bcclient
udp        0      0 255.255.255.255:8097    0.0.0.0:*                           14495/bcclient
udp        0      0 127.0.1.1:53            0.0.0.0:*                           8426/dnsmasq
udp        0      0 192.168.42.255:137      0.0.0.0:*                           12356/nmbd
udp        0      0 192.168.42.24:137       0.0.0.0:*                           12356/nmbd
udp        0      0 0.0.0.0:137             0.0.0.0:*                           12356/nmbd
udp        0      0 192.168.42.255:138      0.0.0.0:*                           12356/nmbd
udp        0      0 192.168.42.24:138       0.0.0.0:*                           12356/nmbd
udp        0      0 0.0.0.0:138             0.0.0.0:*                           12356/nmbd
udp        0      0 0.0.0.0:22359           0.0.0.0:*                           7616/dhclient
udp        0      0 :::57614                :::*                                7616/dhclient
udp        0      0 fe80::265e:beff:fe3b:7405:546 :::*                                7616/dhclient

I was particularly baffled by cups (which is not even an option anywhere), bcclient (which appears to be used in the discovery process, but is not well documented) and the fact that a disabled webserver and a management interface set to HTTPS exclusively still leave two webserver ports (80 and 8080) running. I have no idea what _thttpd_ is, but at least it’s just running on the loopback interface. Why there are two instances of dhclient listening on UDP is also beyond me. I’m not running a server, and the IP addresses are statically configured, so there would also not be any use for dhcp clients.

Another thing that bugs me, are the ports 137/udp, 138/udp, 139/tcp, all of which are for the legacy SMBv1 protocol that I disabled.

Even without any users on that NAS and with no traffic going in or out and with no meaningful processes, I have a sysload over 1:

[~] # uptime
 15:51:38 up 46 min,  load average: 1.60, 1.42, 1.37

So after all of this was not really successful, I thought I should close this up some more. The security tab in QTS is not really doing anything but filtering whole IP addresses, so that’s out. Luckily, the more recent QNAP NAS models come with iptables out of the box, let’s see what’s in there:

[~] # iptables --list
Chain INPUT (policy ACCEPT)
target     prot opt source               destination         

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination         
DROP       all  --  anywhere             anywhere             match-set BRNOIPSET src,dst

OK, Nothing to see here.

On to a solution

Let’s add our own rules. We can use autorun.sh for that, which is present on more recent NAS models. I mostly use this iptables pattern by Vivek Gite, but I’m extending it for other ports.

The precise commands will differ based on your exact NAS model, see the autorun document linked above.

[~] # mount /dev/mmcblk1p6 /tmp/config/
[~] # vi /tmp/config/autorun.sh
[~] # chmod /tmp/config/autorun.sh
[~] # umount /tmp/config/

Here are the contents of my autorun.sh

#!/bin/sh

# Flushing all rules
iptables -F
iptables -X

# Setting default filter policy
iptables -P INPUT DROP
iptables -P OUTPUT DROP
iptables -P FORWARD DROP

# Allow unlimited traffic on loopback
iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT

# Allow incoming ssh and https only
iptables -A INPUT -p tcp -s 0/0 --sport 513:65535 --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp -d 0/0 --sport 22 --dport 513:65535 -m state --state ESTABLISHED -j ACCEPT
iptables -A INPUT -p tcp -s 0/0 --sport 513:65535 --dport 443 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp -d 0/0 --sport 443 --dport 513:65535 -m state --state ESTABLISHED -j ACCEPT

# make sure nothing comes or goes out of this box
iptables -A INPUT -j DROP
iptables -A OUTPUT -j DROP

I like to test these rules first, before activating autorun.sh on a system level. You can just run this file with /tmp/config/autorun.sh and after that you should test if you can still connect via SSH and/or HTTPS.

Your iptables should now look like this:

[~] # iptables --list
Chain INPUT (policy DROP)
target     prot opt source               destination         
ACCEPT     all  --  anywhere             anywhere            
ACCEPT     tcp  --  anywhere             anywhere             tcp spts:login:65535 dpt:ssh state NEW,ESTABLISHED
ACCEPT     tcp  --  anywhere             anywhere             tcp spts:login:65535 dpt:https state NEW,ESTABLISHED
DROP       all  --  anywhere             anywhere            

Chain FORWARD (policy DROP)
target     prot opt source               destination         

Chain OUTPUT (policy DROP)
target     prot opt source               destination         
ACCEPT     all  --  anywhere             anywhere            
ACCEPT     tcp  --  anywhere             anywhere             tcp spt:ssh dpts:login:65535 state ESTABLISHED
ACCEPT     tcp  --  anywhere             anywhere             tcp spt:https dpts:login:65535 state ESTABLISHED
DROP       all  --  anywhere             anywhere            

You can also test if other services are still reachable (which they should not) by connecting to an open port via nc (or any other tool). This test should just throw a timeout after five seconds:

nc -v -w 5 192.168.42.24 631
nc: connect to 192.168.42.24 port 631 (tcp) timed out: Operation now in progress

I can now proceed to and add incoming rules for SAMBA (445/tcp), and outgoing rules for DNS (53/udp), SMTP (587/tcp for me, but 465/tcp is also common) and NTP (123/udp), this is about all I want to do. I will probably also add one more rule for monitoring, but not today. Note that this will also make automatic updating of the NAS impossible for now. I can always manually update firmware, of course.

#!/bin/sh
# CC modifications

# Flushing all rules
iptables -F
iptables -X

# Setting default filter policy
iptables -P INPUT DROP
iptables -P OUTPUT DROP
iptables -P FORWARD DROP

# Allow unlimited traffic on loopback
iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT

# Allow incoming ssh and https only
iptables -A INPUT -p tcp -s 0/0 --sport 513:65535 --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp -d 0/0 --sport 22 --dport 513:65535 -m state --state ESTABLISHED -j ACCEPT
iptables -A INPUT -p tcp -s 0/0 --sport 513:65535 --dport 443 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp -d 0/0 --sport 443 --dport 513:65535 -m state --state ESTABLISHED -j ACCEPT

# Allow incoming SMB connections
iptables -A INPUT -p tcp -s 0/0 --sport 513:65535 --dport 445 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp -d 0/0 --sport 445 --dport 513:65535 -m state --state ESTABLISHED -j ACCEPT

# Allow DNS to our own server
iptables -A OUTPUT -p udp -s 0/0 --sport 513:65535 --dport 53 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -p udp -d 0/0 --sport 53 --dport 513:65535 -m state --state ESTABLISHED -j ACCEPT

# Allow outgoing SMTP on Port 587
iptables -A OUTPUT -p tcp -s 0/0 --sport 513:65535 --dport 587 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -p tcp -d 0/0 --sport 587 --dport 513:65535 -m state --state ESTABLISHED -j ACCEPT

# Allow outgoing NTP requests
iptables -A OUTPUT -p udp -s 0/0 --sport 513:65535 --dport 123 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -p udp -d 0/0 --sport 123 --dport 513:65535 -m state --state ESTABLISHED -j ACCEPT


# make sure nothing comes or goes out of this box
iptables -A INPUT -j DROP
iptables -A OUTPUT -j DROP

so now my iptables rules look like this:

[~] # iptables --list
Chain INPUT (policy DROP)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere
ACCEPT     tcp  --  anywhere             anywhere             tcp spts:login:65535 dpt:ssh state NEW,ESTABLISHED
ACCEPT     tcp  --  anywhere             anywhere             tcp spts:login:65535 dpt:https state NEW,ESTABLISHED
ACCEPT     tcp  --  anywhere             anywhere             tcp spts:login:65535 dpt:445 state NEW,ESTABLISHED
ACCEPT     udp  --  anywhere             anywhere             udp spt:domain dpts:who:65535 state ESTABLISHED
ACCEPT     tcp  --  anywhere             anywhere             tcp spt:587 dpts:login:65535 state ESTABLISHED
ACCEPT     udp  --  anywhere             anywhere             udp spt:ntp dpts:who:65535 state ESTABLISHED
DROP       all  --  anywhere             anywhere

Chain FORWARD (policy DROP)
target     prot opt source               destination

Chain OUTPUT (policy DROP)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere
ACCEPT     tcp  --  anywhere             anywhere             tcp spt:ssh dpts:login:65535 state ESTABLISHED
ACCEPT     tcp  --  anywhere             anywhere             tcp spt:https dpts:login:65535 state ESTABLISHED
ACCEPT     tcp  --  anywhere             anywhere             tcp spt:445 dpts:login:65535 state ESTABLISHED
ACCEPT     udp  --  anywhere             anywhere             udp spts:who:65535 dpt:domain state NEW,ESTABLISHED
ACCEPT     tcp  --  anywhere             anywhere             tcp spts:login:65535 dpt:587 state NEW,ESTABLISHED
ACCEPT     udp  --  anywhere             anywhere             udp spts:who:65535 dpt:ntp state NEW,ESTABLISHED
DROP       all  --  anywhere             anywhere

Please note that this disables a lot of things that you may want to use but it should make the attack surface a lot smaller. In particular automatic software updates and the QNAP App Center won’t work with these exact settings. I may lock down the accessible ports even more limiting them to a known set of ip addresses, but for now it’s good enough to connect the NAS to my regular network once again. I can’t guarantee that this will prevent future infections, as we don’t have conclusive information on the infection vector so far.

This may not be the ruleset for you, but you will probably be able to adapt it from here.

Open questions

So, why are all of these ports even open? Why can’t I deactivate more of them from within the management interface? How was firmware 4.4.2 infected? How can I trust the device after an infection? How would I verify that only exactly QNAP’s QTS is running and no parts of any malware made it into a BIOS and/or firmware and/or virtualize QTS itself while remaining active?

While I can’t answer these questions, and can’t give you any support with your individual NAS, please let me know if this works for you or if you have additional measures in place.


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Claudius Coenen is a tech-enthusiast. He's writing on all kinds of topics, including programming, technology, gadgets and media.

This site features his occasional articles, findings, documentations.

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