Ubuntu 20でFail2ban sshdを設定してみてください。
# fail2ban-client status sshd
Status for the jail: sshd
|- Filter
| |- Currently failed: 0
| |- Total failed: 0
| `- File list: /var/log/auth.log
`- Actions
|- Currently banned: 8
|- Total banned: 8
`- Banned IP list: 112.85.42.185 114.198.132.36 184.99.163.554 2.176.241.217 221.181.185.135 221.181.185.148 45.141.84.126 49.88.112.77
禁止されているすべてのIPは手動で追加されますfail2ban-client set sshd banip <IP>。
刑務所：
[sshd]
mode = aggressive
filter = sshd
port = ssh
logpath = %(sshd_log)s
backend = %(sshd_backend)s
enabled = true
maxretry = 1
デフォルトの sshd 定義を使用します。
# cat /etc/fail2ban/filter.d/sshd.conf | grep -v ^# | grep .
[INCLUDES]
before = common.conf
[DEFAULT]
_daemon = sshd
__pref = (?:(?:error|fatal): (?:PAM: )?)?
__suff = (?: (?:port \d+|on \S+|\[preauth\])){0,3}\s*
__on_port_opt = (?: (?:port \d+|on \S+)){0,2}
__authng_user = (?: (?:invalid|authenticating) user <F-USER>\S+|.+?</F-USER>)?
__alg_match = (?:(?:\w+ (?!found\b)){0,2}\w+)
__pam_auth = pam_[a-z]+
[Definition]
prefregex = ^<F-MLFID>%(__prefix_line)s</F-MLFID>%(__pref)s<F-CONTENT>.+</F-CONTENT>$
cmnfailre = ^[aA]uthentication (?:failure|error|failed) for <F-USER>.*</F-USER> from <HOST>( via \S+)?%(__suff)s$
^User not known to the underlying authentication module for <F-USER>.*</F-USER> from <HOST>%(__suff)s$
^Failed publickey for invalid user <F-USER>(?P<cond_user>\S+)|(?:(?! from ).)*?</F-USER> from <HOST>%(__on_port_opt)s(?: ssh\d*)?(?(cond_user): |(?:(?:(?! from ).)*)$)
^Failed \b(?!publickey)\S+ for (?P<cond_inv>invalid user )?<F-USER>(?P<cond_user>\S+)|(?(cond_inv)(?:(?! from ).)*?|[^:]+)</F-USER> from <HOST>%(__on_port_opt)s(?: ssh\d*)?(?(cond_user): |(?:(?:(?! from ).)*)$)
^<F-USER>ROOT</F-USER> LOGIN REFUSED FROM <HOST>
^[iI](?:llegal|nvalid) user <F-USER>.*?</F-USER> from <HOST>%(__suff)s$
^User <F-USER>.+</F-USER> from <HOST> not allowed because not listed in AllowUsers%(__suff)s$
^User <F-USER>.+</F-USER> from <HOST> not allowed because listed in DenyUsers%(__suff)s$
^User <F-USER>.+</F-USER> from <HOST> not allowed because not in any group%(__suff)s$
^refused connect from \S+ \(<HOST>\)
^Received <F-MLFFORGET>disconnect</F-MLFFORGET> from <HOST>%(__on_port_opt)s:\s*3: .*: Auth fail%(__suff)s$
^User <F-USER>.+</F-USER> from <HOST> not allowed because a group is listed in DenyGroups%(__suff)s$
^User <F-USER>.+</F-USER> from <HOST> not allowed because none of user's groups are listed in AllowGroups%(__suff)s$
^<F-NOFAIL>%(__pam_auth)s\(sshd:auth\):\s+authentication failure;</F-NOFAIL>(?:\s+(?:(?:logname|e?uid|tty)=\S*)){0,4}\s+ruser=<F-ALT_USER>\S*</F-ALT_USER>\s+rhost=<HOST>(?:\s+user=<F-USER>\S*</F-USER>)?%(__suff)s$
^(error: )?maximum authentication attempts exceeded for <F-USER>.*</F-USER> from <HOST>%(__on_port_opt)s(?: ssh\d*)?%(__suff)s$
^User <F-USER>.+</F-USER> not allowed because account is locked%(__suff)s
^<F-MLFFORGET>Disconnecting</F-MLFFORGET>(?: from)?(?: (?:invalid|authenticating)) user <F-USER>\S+</F-USER> <HOST>%(__on_port_opt)s:\s*Change of username or service not allowed:\s*.*\[preauth\]\s*$
^<F-MLFFORGET>Disconnecting</F-MLFFORGET>: Too many authentication failures(?: for <F-USER>.+?</F-USER>)?%(__suff)s$
^<F-NOFAIL>Received <F-MLFFORGET>disconnect</F-MLFFORGET></F-NOFAIL> from <HOST>%(__on_port_opt)s:\s*11:
<mdre-<mode>-other>
^<F-MLFFORGET><F-MLFGAINED>Accepted \w+</F-MLFGAINED></F-MLFFORGET> for <F-USER>\S+</F-USER> from <HOST>(?:\s|$)
mdre-normal =
mdre-normal-other = ^<F-NOFAIL><F-MLFFORGET>(Connection closed|Disconnected)</F-MLFFORGET></F-NOFAIL> (?:by|from)%(__authng_user)s <HOST>(?:%(__suff)s|\s*)$
mdre-ddos = ^Did not receive identification string from <HOST>
^Bad protocol version identification '.*' from <HOST>
^Connection <F-MLFFORGET>reset</F-MLFFORGET> by <HOST>
^<F-NOFAIL>SSH: Server;Ltype:</F-NOFAIL> (?:Authname|Version|Kex);Remote: <HOST>-\d+;[A-Z]\w+:
^Read from socket failed: Connection <F-MLFFORGET>reset</F-MLFFORGET> by peer
mdre-ddos-other = ^<F-MLFFORGET>(Connection closed|Disconnected)</F-MLFFORGET> (?:by|from)%(__authng_user)s <HOST>%(__on_port_opt)s\s+\[preauth\]\s*$
mdre-extra = ^Received <F-MLFFORGET>disconnect</F-MLFFORGET> from <HOST>%(__on_port_opt)s:\s*14: No supported authentication methods available
^Unable to negotiate with <HOST>%(__on_port_opt)s: no matching <__alg_match> found.
^Unable to negotiate a <__alg_match>
^no matching <__alg_match> found:
mdre-extra-other = ^<F-MLFFORGET>Disconnected</F-MLFFORGET>(?: from)?(?: (?:invalid|authenticating)) user <F-USER>\S+|.*?</F-USER> <HOST>%(__on_port_opt)s \[preauth\]\s*$
mdre-aggressive = %(mdre-ddos)s
%(mdre-extra)s
mdre-aggressive-other = %(mdre-ddos-other)s
cfooterre = ^<F-NOFAIL>Connection from</F-NOFAIL> <HOST>
failregex = %(cmnfailre)s
<mdre-<mode>>
%(cfooterre)s
mode = aggressive
ignoreregex =
maxlines = 1
journalmatch = _SYSTEMD_UNIT=sshd.service + _COMM=sshd
このフィルタは正規表現と一致しているようです（> 3000一致）。
# fail2ban-regex /var/log/auth.log /etc/fail2ban/filter.d/sshd.conf
Running tests
=============
Use failregex filter file : sshd, basedir: /etc/fail2ban
Use maxlines : 1
Use datepattern : Default Detectors
Use log file : /var/log/auth.log
Use encoding : UTF-8
Results
=======
Failregex: 4571 total
|- #) [# of hits] regular expression
| 1) [942] ^[aA]uthentication (?:failure|error|failed) for <F-USER>.*</F-USER> from <HOST>( via \S+)?(?: (?:port \d+|on \S+|\[preauth\])){0,3}\s*$
| 4) [84] ^Failed \b(?!publickey)\S+ for (?P<cond_inv>invalid user )?<F-USER>(?P<cond_user>\S+)|(?(cond_inv)(?:(?! from ).)*?|[^:]+)</F-USER> from <HOST>(?: (?:port \d+|on \S+)){0,2}(?: ssh\d*)?(?(cond_user): |(?:(?:(?! from ).)*)$)
| 6) [843] ^[iI](?:llegal|nvalid) user <F-USER>.*?</F-USER> from <HOST>(?: (?:port \d+|on \S+|\[preauth\])){0,3}\s*$
| 14) [942] ^<F-NOFAIL>pam_[a-z]+\(sshd:auth\):\s+authentication failure;</F-NOFAIL>(?:\s+(?:(?:logname|e?uid|tty)=\S*)){0,4}\s+ruser=<F-ALT_USER>\S*</F-ALT_USER>\s+rhost=<HOST>(?:\s+user=<F-USER>\S*</F-USER>)?(?: (?:port \d+|on \S+|\[preauth\])){0,3}\s*$
| 19) [402] ^<F-NOFAIL>Received <F-MLFFORGET>disconnect</F-MLFFORGET></F-NOFAIL> from <HOST>(?: (?:port \d+|on \S+)){0,2}:\s*11:
| 20) [1329] ^<F-MLFFORGET>(Connection closed|Disconnected)</F-MLFFORGET> (?:by|from)(?: (?:invalid|authenticating) user <F-USER>\S+|.+?</F-USER>)? <HOST>(?: (?:port \d+|on \S+)){0,2}\s+\[preauth\]\s*$
| 21) [8] ^<F-MLFFORGET><F-MLFGAINED>Accepted \w+</F-MLFGAINED></F-MLFFORGET> for <F-USER>\S+</F-USER> from <HOST>(?:\s|$)
| 24) [6] ^Connection <F-MLFFORGET>reset</F-MLFFORGET> by <HOST>
| 28) [15] ^Unable to negotiate with <HOST>(?: (?:port \d+|on \S+)){0,2}: no matching (?:(?:\w+ (?!found\b)){0,2}\w+) found.
`-
Ignoreregex: 0 total
Date template hits:
|- [# of hits] date format
| [5185] {^LN-BEG}(?:DAY )?MON Day %k:Minute:Second(?:\.Microseconds)?(?: ExYear)?
`-
Lines: 5185 lines, 1352 ignored, 3216 matched, 617 missed
[processed in 0.34 sec]
Ignored line(s): too many to print. Use --print-all-ignored to print all 1352 lines
Missed line(s): too many to print. Use --print-all-missed to print all 617 lines
しかし、何が起こってもIPはブロックされません！
*次の項目を設定したと追加しましたsshd_config。
PermitRootLogin prohibit-password
ChallengeResponseAuthentication yes
PasswordAuthentication no
そしてGoogle 2FAを追加しました/etc/pam.d/sshd。
auth required pam_google_authenticator.so