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Harden Nextcloud 17+ with Fail2Ban, GUI and WebDAV - Ubuntu 18.04

Short how-to harden your Nextcloud Server with Fail2Ban

Install fail2ban:

sudo apt update && sudo apt install fail2ban -y

Create the Nextcloud-filter:

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

Paste the following lines, this will cover GUI Failed login and WebDAV:

[Definition]
failregex=^{.*Login failed: .* \(Remote IP: <HOST>\).*}$
ignoreregex =

If you want to protect also from direct IP access or wrong Domain name access configure it as below (as per https://github.com/nextcloud/vm/blob/master/apps/fail2ban.sh)

[Definition]
failregex=^{.*Login failed: .* \(Remote IP: <HOST>\).*}$
          ^.*\"remoteAddr\":\"<HOST>\".*Trusted domain error.*\$
ignoreregex =

Create a new jail:

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

Paste the following rows:

[nextcloud]
backend = auto
enabled = true
port = 80,443
protocol = tcp
filter = nextcloud
#Number of retrys before to ban
maxretry = 3
#time in seconds
bantime = 36000
findtime = 36000
#Log path, on Ubuntu usually following
logpath = /var/www/nextcloud/data/nextcloud.log

Re-start the fail2ban-service:

sudo service fail2ban restart

and enjoy your Nextcloud-Server!

P.S. Pattern For GUI:

#Nextcloud 17+
{"reqId":"BRHKHyh1lVFon5D33u4K","level":2,"time":"2020-01-13T12:34:00+00:00","remoteAddr":"10.11.12.13","user":"--","app":"no app in context","method":"POST","url":"\/index.php\/login","message":"Login failed: Tralololjlkl (Remote IP: 10.11.12.13)","userAgent":"Mozilla\/5.0 (Windows NT 10.0; Win64; x64; rv:72.0) Gecko\/20100101 Firefox\/72.0","version":"17.0.2.1"}
#Nextcloud <= 16
{"reqId":"bFnTdevf7ZdCMQ5ddmNl","level":2,"time":"2019-04-03T21:49:30+00:00","remoteAddr":"10.11.12.13","user":"--","app":"core","method":"POST","url":"\/index.php\/login","message":"Login failed: 'Tralololjlkl' (Remote IP: '10.11.12.13')","userAgent":"Mozilla\/5.0 (X11; Ubuntu; Linux x86_64; rv:66.0) Gecko\/20100101 Firefox\/66.0","version":"15.0.5.3"}

For WebDav:

#Nextcloud 17+

#Nextcloud <= 16
{"reqId":"Q4wX3I4LOUeuMV4wRK91","level":2,"time":"2019-04-03T22:14:11+00:00","remoteAddr":"10.11.12.13","user":"--","app":"core","method":"GET","url":"\/remote.php\/dav\/files","message":"Login failed: 'test' (Remote IP: '10.11.12.13')","userAgent":"Mozilla\/5.0 (X11; Ubuntu; Linux x86_64; rv:66.0) Gecko\/20100101 Firefox\/66.0","version":"15.0.5.3"}

Test:

fail2ban-regex /var/nextcloud/data/nextcloud.log /etc/fail2ban/filter.d/nextcloud.conf --print-all-matched

Running tests
=============

Use   failregex filter file : Nextcloud, basedir: /etc/fail2ban
Use         log file : /var/nextcloud/data/nextcloud.log
Use         encoding : UTF-8


Results
=======

Failregex: 1 total
|-  #) [# of hits] regular expression
|   1) [1] ^{.*Login failed: .* \(Remote IP: <HOST>\).*}$
`-

Ignoreregex: 0 total

Date template hits:
|- [# of hits] date format
|  [355] ExYear(?P<_sep>[-/.])Month(?P=_sep)Day(?:T|  ?)24hour:Minute:Second(?:[.,]Microseconds)?(?:\s*Zone offset)?
`-

Lines: 355 lines, 0 ignored, 1 matched, 354 missed
[processed in 1.40 sec]

|- Matched line(s):
|  {"reqId":"BRHKHyh1lVFon5D33u4K","level":2,"time":"2020-01-13T12:34:00+00:00","remoteAddr":"10.11.12.13","user":"--","app":"no app in context","method":"POST","url":"\/index.php\/login","message":"Login failed: Tralololjlkl (Remote IP: 10.11.12.13)","userAgent":"Mozilla\/5.0 (Windows NT 10.0; Win64; x64; rv:72.0) Gecko\/20100101 Firefox\/72.0","version":"17.0.2.1"}
`-
Missed line(s): too many to print.  Use --print-all-missed to print all 354 lines
@tiagofreire-pt

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tiagofreire-pt commented Jul 18, 2019

For Univention Appliances the logfile is in: /var/lib/univention-appcenter/apps/nextcloud/data/nextcloud-data/nextcloud.log

@Cronixx

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Cronixx commented Jan 8, 2020

The Pattern did change: There are no '' around the login-name and the ip anymore.

[Definition]
failregex=^{.Login failed: . (Remote IP: ).*}$
ignoreregex =

@GAS85

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GAS85 commented Jan 13, 2020

Thank!
Did it changed for Trusted Domain error also?

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