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Setup Fail2ban for NextCloud

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Running NextCloud or OwnCloud online comes with some risk, as with any online service. It’s important that your installation remains secure against hackers (or at least as secure as it can be). I’ve opted to implement fail2ban in order to help secure it using some custom rules. It’s worth noting that NextCloud does block unwanted login attempts itself through the application, but you’re having to trust application level security. I feel far safer having fail2ban implement firewall rules to prevent access to anyone probing the server.

First thing to do is create the NextCloud filter configuration file. This file will contain the regex that’s used to scan the logs for anything we don’t like the look of in order to block attacking hosts. My understanding is that this file can remain the same for OwnCloud, although I do not currently have a running instance of it to check.

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sudo nano /etc/fail2ban/filter.d/nextcloud.conf

Add the following to the file:

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[Definition]
failregex=^{"reqId":".<em>","remoteAddr":".</em>","app":"core","message":"Login failed: '.<em>' &#40;Remote IP: '<HOST>'&#41;","level":2,"time":".</em>"}$
        ^{"reqId":".<em>","level":2,"time":".</em>","remoteAddr":".<em>","app":"core".</em>","message":"Login failed: '.<em>' &#40;Remote IP: '<HOST>'&#41;".</em>}$
        ^.<em>\"remoteAddr\":\"<HOST>\".</em>Trusted domain error.*$

There are three regular expressions included here. The first and second checks for login failures, and flags the source IP. The third checks for trusted domain errors – which are usually a result of bots accessing your installation via it’s IP, not via it’s domain (thus, suspicious and I wanted to block them).

Once the file is saved, you can test what the filter would report by running the following command. This is entirely optional (although would help identify issues) and isn’t required for the rest of the steps to work.

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sudo fail2ban-regex /var/nextcloud/data/nextcloud.log /etc/fail2ban/filter.d/nextcloud.conf -v

Next, the configuration file needs setup to activate the configurations we’ve just created. Never edit the Fail2ban jail.conf file, it’s likely to be overridden on upgrades. Always create a “.local” file, ideally a separate one for each application or rule you’re setting up (why? because it makes things more organised and easier to manage one rule over another!) inside the jail.d directory. With this in mind, create a nextcloud (or owncloud) file:

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sudo nano /etc/fail2ban/jail.d/nextcloud.local

And add the following to it:

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[nextcloud]
ignoreip = 192.168.1.0/24
backend = auto
enabled = true
port = 80,443
protocol = tcp
filter = nextcloud
maxretry = 3
bantime = 36000
findtime = 36000
logpath = /var/nextcloud/data/nextcloud.log

Make sure your ignoreip is your local subnet or IP address. I opted to allow my whole LAN to access it without being auto-blocked. I’ve enabled the rule, set the ports to 80 (HTTP) and 443 (HTTPS) and configured ban times, etc. The most important things are the filter which should match the name of the file that was created inside the filter.d directory (excluding extension), and the log path, which may vary by installation. This path is the default for Ubuntu.

Once done, run the following command to restart nextcloud:

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sudo service fail2ban restart

You can check the status of the jail by running:

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sudo fail2ban-client status nextcloud

You’ll see something similar to this:

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Status for the jail: nextcloud
|- Filter
|  |- Currently failed: 13
|  |- Total failed: 82
|  `- File list:    /var/nextcloud/data/nextcloud.log
`- Actions
   |- Currently banned: 0
   |- Total banned: 5
   `- Banned IP list:

Setting up a KVM host on Ubuntu 18.04 with bridged networking

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Since the launch of Ubuntu server 18.04, I’ve had a few people ask me how to setup bridged networking since the changeover to netplan for networking. The setup’s actually quite straight forwards once you know how. Start out by installing KVM and associated packages (I’m assuming you’re on a fresh Ubuntu 18.04 box):

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sudo apt install bridge-utils qemu-kvm libvirt-bin

You should now be able to access virsh, to test it just run the command to list the virtual machines on the host (this will of course output an empty list. We just want to make sure the command hasn’t failed before going further):

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virsh list --all

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<h2> Id    Name                           State</h2>

Now edit the netplan file for the networking configuration of the host system:

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sudo nano /etc/netplan/50-cloud-init.yaml

The configuration should be edited to look similar to this:

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network:
    ethernets:
        eno1:
            addresses: []
            dhcp4: true
            optional: true
    version: 2
    bridges:
        br0:
            interfaces: [eno1]
            dhcp4: true
            parameters:
                stp: false
                forward-delay: 0

We’re basically defining a single ethernet port (eno1) and assigning it to a bride. Note that you can check your ethernet port name using the ‘ip address’ command on the command line and it will return your network adapters and IP addresses. It should be resonably obvious which one is your ethernet adapter from the list!

It’s worth noting that in this setup, we’re allowing DHCP to allocate addresses to the machine. If this isn’t what you want, take a look at the netplan examples here: https://netplan.io/examples

You can apply these change using:

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sudo netplan apply

And check it’s working:

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ip address

or

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networkctl list

If you’ve gotten this far without a network issue, you should be able to create machines using your favorite tool. I use Virtual Machine Manager (https://virt-manager.org/) which provides a reasonable user interface as well as remote management via SSH.

Setting up a Bond and Bridge in Netplan on Ubuntu 18.04

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For some of my Ubuntu 18.04 servers, I need to run KVM virtual machines which require a bridge to the network so the machines get public LAN IP addresses and aren’t hidden behind NAT. With the server configuration for both my co-location and servers at work the network interfaces are all bonded for fail-over. This means I need a bond to have a bridge ontop of it for the virtual machines to get public IP addresses, while still allowing for failover of the network connection in the event of a network failure.

Research

There are some good examples of setting up netplan here: https://netplan.io/examples

They have a bridge example:

Netplan bridge example
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network:
  version: 2
  renderer: networkd
  bridges:
    br0:
      dhcp4: yes
      interfaces:
        - enp3s0

And a bond example:

Netplan bond example
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network:
  version: 2
  renderer: networkd
  bonds:
    bond0:
      dhcp4: yes
      interfaces:
        - enp3s0
        - enp4s0
      parameters:
        mode: active-backup
        primary: enp3s0

But there’s not a clear indication of how to amalgamate the two.

A bond and a bridge

Here’s what I’ve ended up with in ‘/etc/netplan/50-cloud-init.yaml’:

Netplan bridge and bond
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network:
    bridges:
        br0:
            addresses:
            - 192.168.10.30
            dhcp4: false
            gateway4: 192.168.10.1
            nameservers:
                addresses:
                - 192.168.10.1
                - 192.168.10.2
                search: []
            interfaces:
                - bond0
    bonds:
        bond0:
            interfaces:
            - eno1
            - eno2
            parameters:
                mode: active-backup
    ethernets:
        eno1:
            addresses: []
            dhcp4: false
            dhcp6: false
        eno2:
            addresses: []
            dhcp4: false
            dhcp6: false

Note that I’ve obviously defined static IP addresses, but this isn’t a requirement. Just set ‘dhcp4: true’ and remove the ‘address’, ‘gateway’ and ‘nameserver’ sections if you’re using DHCP.

Once the file’s got that setup in it, it’s possible to run:

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sudo netplan apply

and you should be able to run ‘networkctl list’ to check the bridge and bond are setup.

Fail2ban does not enable some rules

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While setting up a webserver, I noticed that

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fail2ban-client status

 did not list all of the rules that I’d configured in

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jail.d

. Althought configuration files were added to the directory, the status wasn’t showing them listed, so it hadn’t activated the jails. Running

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service fail2ban restart

 didn’t add them either.

After spending some time researching, some people suggest changing the backend used in fail2ban from auto to polling in jail.conf. Since you shouldn’t edit jail.conf on a debian based system, I tried creating a new file 

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nano /etc/fail2ban/jail.local

 and adding the line

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backend = polling

. This actually prevented the fail2ban service from starting for me. The errors in

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systemctl status fail2ban.service

didn’t show anything useful as to the cause of the error. In the end I reverted this change.

running

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fail2ban-client reload

 did present error messages detailing which rule couldn’t be activated:

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ERROR No file(s) found for glob /var/log/apache2/*.log
ERROR Failed during configuration: Have not found any log file for apache-xmlrpc jail

This then meant I was able to investigate the

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jail.d

 config file with the rule indicated as causing the problem and correct the log file path.

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fail2ban-client status

 then shows the correct jails running.

mount disk image created with dd using ubuntu

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If you’ve cloned a whole drive using dd and you need to access one of the partitions on it here are some steps to follow in order to gain access:

Find the partition start sectors using fdisk -b512 -l. Note that you’re explicitly setting the sector size to 512 bytes and you’ll need to change your command to match your own image file.

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fdisk -b512 -l backup_sata.img

You should get output similar to this (note I’ve truncated it to only show the appropriate output):

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Device         Boot     Start       End   Sectors   Size Id Type
backup_sata.img1 *         2048    206847    204800   100M  7 HPFS/NTFS/exFAT
backup_sata.img2         206848 237185023 236978176   113G  7 HPFS/NTFS/exFAT
backup_sata.img3      237185024 588070911 350885888 167.3G  f W95 Ext'd (LBA)
backup_sata.img4      588070912 625137663  37066752  17.7G 27 Hidden NTFS WinRE
backup_sata.img5      237187072 588070911 350883840 167.3G  7 HPFS/NTFS/exFAT

Normally sector are 512 bytes, so you can calculate the offset you need in the next command with:

start * 512 = offset

So if you want to mount backup_sata.img5 (partition 5 of the backup image) you’d run 237187072×512=121439780864:

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mount -o ro,loop,offset=121439780864 backup_sata.img /backup_sata

Remember to have created /backup_sata or whatever directory you’re mounting to first!