According to jail.conf we actually need to separate multiple values
with spaces instead of commas. On some versions of fail2ban this is
a fatal error:
> CRITICAL Unhandled exception in Fail2Ban:
> Traceback (most recent call last):
> File "/usr/lib/python3/dist-packages/fail2ban/server/jailthread.py", line 66, in run_with_except_hook
> run(*args, **kwargs)
> File "/usr/lib/python3/dist-packages/fail2ban/server/filtersystemd.py", line 246, in run
> *self.formatJournalEntry(logentry))
> File "/usr/lib/python3/dist-packages/fail2ban/server/filter.py", line 432, in processLineAndAdd
> if self.inIgnoreIPList(ip, log_ignore=True):
> File "/usr/lib/python3/dist-packages/fail2ban/server/filter.py", line 371, in inIgnoreIPList
> "(?<=b)1+", bin(DNSUtils.addr2bin(s[1]))).group())
> File "/usr/lib/python3/dist-packages/fail2ban/server/filter.py", line 928, in addr2bin
> return struct.unpack("!L", socket.inet_aton(ipstring))[0]
> OSError: illegal IP address string passed to inet_aton
This affects (at least) fail2ban 0.9.3 on Ubuntu 16.04, but I never
noticed.
This is active banning of IPs that are brute forcing login attempts
to SSH, versus the passive banning of 10,000 abusive IPs from the
abuseipdb.com blacklist. For now I am banning IPs that fail to log
in successfully more than twelve times in a one-hour period, but
these settings might change, and I can override them at the group
and host level if needed.
Currently this works for CentOS 7, Ubuntu 16.04, and Ubuntu 18.04,
with minor differences in the systemd configuration due to older
versions on some distributions.
You can see the status of the jail like this:
# fail2ban-client status sshd
Status for the jail: sshd
|- Filter
| |- Currently failed: 0
| |- Total failed: 0
| `- Journal matches: _SYSTEMD_UNIT=sshd.service + _COMM=sshd
`- Actions
|- Currently banned: 1
|- Total banned: 1
`- Banned IP list: 106.13.112.20
You can unban IPs like this:
# fail2ban-client set sshd unbanip 106.13.112.20
Alan Orth