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* Security
** Switch APT to HTTPS
~sudo sed -i 's/http:/https:/' /etc/apt/sources.list~
Granted, the repository signature provides enough protection; still,
no sense in wasting bandwidth and CPU if someone is meddling.
** Tweak root access
On OVH's Debian image:
- The =root= account has no password.
- =PermitRootLogin= defaults to =prohibit-password=: set it to =no=.
** Enable fail2ban
~lastb~ says there's about 4000 login attempts per day; that makes
=/var/log/btmp= much bigger than it needs to be.
Debian's fail2ban comes with a jail for ~sshd~, so it's just a matter
of ~apt install fail2ban~.
** Tweak user accounts
=debian= seems mildly popular among bots looking for valid usernames.
Ideally I'd just rename the =debian= account, but renaming does not
seem to be a very well-defined operation: ~usermod --login $name
--move-home --home /home/$name debian~ gets partway there, but leaves
a bunch of miscellany to take care of (e.g. sudoers).
So instead, I'll
- create my own user account: ~sudo adduser $name~
- add it to all groups =debian= belongs to:
#+begin_src sh
groups=$(groups | sed -e 's/ *debian *//' -e 's/ /,/g')
sudo usermod --append --groups ${groups} ${name}
#+end_src
- only allow password authentication over SSH for this new user
account:
#+begin_src conf
PasswordAuthentication no
Match User …
PasswordAuthentication yes
#+end_src
* Web server
With the following files in =$HOME=:
#+begin_src conf
# nginx-botsearch.local
[Init]
block = \S*(php|wp-|wordpress|jenkins|hudson|sql|boaform)[^,]*
[Definition]
# Change from distro: just remove the leading slash before <block>.
failregex = ^<HOST> \- \S+ \[\] \"(GET|POST|HEAD) <block> \S+\" 404 .+$
^ \[error\] \d+#\d+: \*\d+ (\S+ )?\"\S+\" (failed|is not found) \(2\: No such file or directory\), client\: <HOST>\, server\: \S*\, request: \"(GET|POST|HEAD) \/<block> \S+\"\, .*?$
# jail.local
[nginx-http-auth]
enabled = true
[nginx-botsearch]
enabled = true
logpath = /var/log/nginx/access.log
#+end_src
Do:
#+begin_src sh
sudo apt install nginx
sudo cp ~/nginx-botsearch.local /etc/fail2ban/filter.d/
sudo cp ~/jail.local /etc/fail2ban/
sudo systemctl restart fail2ban
#+end_src
Check how these rules fare against real bot searches with
~fail2ban-regex /var/log/nginx/access.log
/etc/fail2ban/filter.d/nginx-botsearch.local~.
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