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137 lines
7.3 KiB
137 lines
7.3 KiB
2 years ago
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# Fail2Ban filter for openssh
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#
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# If you want to protect OpenSSH from being bruteforced by password
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# authentication then get public key authentication working before disabling
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# PasswordAuthentication in sshd_config.
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#
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#
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# "Connection from <HOST> port \d+" requires LogLevel VERBOSE in sshd_config
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#
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[INCLUDES]
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# Read common prefixes. If any customizations available -- read them from
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# common.local
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before = common.conf
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[DEFAULT]
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_daemon = sshd
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# optional prefix (logged from several ssh versions) like "error: ", "error: PAM: " or "fatal: "
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__pref = (?:(?:error|fatal): (?:PAM: )?)?
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# optional suffix (logged from several ssh versions) like " [preauth]"
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#__suff = (?: port \d+)?(?: \[preauth\])?\s*
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__suff = (?: (?:port \d+|on \S+|\[preauth\])){0,3}\s*
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__on_port_opt = (?: (?:port \d+|on \S+)){0,2}
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# close by authenticating user:
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__authng_user = (?: (?:invalid|authenticating) user <F-USER>\S+|.*?</F-USER>)?
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# for all possible (also future) forms of "no matching (cipher|mac|MAC|compression method|key exchange method|host key type) found",
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# see ssherr.c for all possible SSH_ERR_..._ALG_MATCH errors.
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__alg_match = (?:(?:\w+ (?!found\b)){0,2}\w+)
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# PAM authentication mechanism, can be overridden, e. g. `filter = sshd[__pam_auth='pam_ldap']`:
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__pam_auth = pam_[a-z]+
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[Definition]
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prefregex = ^<F-MLFID>%(__prefix_line)s</F-MLFID>%(__pref)s<F-CONTENT>.+</F-CONTENT>$
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cmnfailre = ^[aA]uthentication (?:failure|error|failed) for <F-USER>.*</F-USER> from <HOST>( via \S+)?%(__suff)s$
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^User not known to the underlying authentication module for <F-USER>.*</F-USER> from <HOST>%(__suff)s$
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<cmnfailre-failed-pub-<publickey>>
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^Failed <cmnfailed> 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 ).)*)$)
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^<F-USER>ROOT</F-USER> LOGIN REFUSED FROM <HOST>
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^[iI](?:llegal|nvalid) user <F-USER>.*?</F-USER> from <HOST>%(__suff)s$
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^User <F-USER>\S+|.*?</F-USER> from <HOST> not allowed because not listed in AllowUsers%(__suff)s$
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^User <F-USER>\S+|.*?</F-USER> from <HOST> not allowed because listed in DenyUsers%(__suff)s$
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^User <F-USER>\S+|.*?</F-USER> from <HOST> not allowed because not in any group%(__suff)s$
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^refused connect from \S+ \(<HOST>\)
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^Received <F-MLFFORGET>disconnect</F-MLFFORGET> from <HOST>%(__on_port_opt)s:\s*3: .*: Auth fail%(__suff)s$
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^User <F-USER>\S+|.*?</F-USER> from <HOST> not allowed because a group is listed in DenyGroups%(__suff)s$
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^User <F-USER>\S+|.*?</F-USER> from <HOST> not allowed because none of user's groups are listed in AllowGroups%(__suff)s$
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^<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$
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^maximum authentication attempts exceeded for <F-USER>.*</F-USER> from <HOST>%(__on_port_opt)s(?: ssh\d*)?%(__suff)s$
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^User <F-USER>\S+|.*?</F-USER> not allowed because account is locked%(__suff)s
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^<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*$
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^Disconnecting: Too many authentication failures(?: for <F-USER>\S+|.*?</F-USER>)?%(__suff)s$
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^<F-NOFAIL>Received <F-MLFFORGET>disconnect</F-MLFFORGET></F-NOFAIL> from <HOST>%(__on_port_opt)s:\s*11:
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<mdre-<mode>-other>
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^<F-MLFFORGET><F-MLFGAINED>Accepted \w+</F-MLFGAINED></F-MLFFORGET> for <F-USER>\S+</F-USER> from <HOST>(?:\s|$)
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cmnfailed-any = \S+
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cmnfailed-ignore = \b(?!publickey)\S+
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cmnfailed-invalid = <cmnfailed-ignore>
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cmnfailed-nofail = (?:<F-NOFAIL>publickey</F-NOFAIL>|\S+)
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cmnfailed = <cmnfailed-<publickey>>
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mdre-normal =
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# used to differentiate "connection closed" with and without `[preauth]` (fail/nofail cases in ddos mode)
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mdre-normal-other = ^<F-NOFAIL><F-MLFFORGET>(Connection closed|Disconnected)</F-MLFFORGET></F-NOFAIL> (?:by|from)%(__authng_user)s <HOST>(?:%(__suff)s|\s*)$
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mdre-ddos = ^Did not receive identification string from <HOST>
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^kex_exchange_identification: (?:[Cc]lient sent invalid protocol identifier|[Cc]onnection closed by remote host)
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^Bad protocol version identification '.*' from <HOST>
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^<F-NOFAIL>SSH: Server;Ltype:</F-NOFAIL> (?:Authname|Version|Kex);Remote: <HOST>-\d+;[A-Z]\w+:
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^Read from socket failed: Connection <F-MLFFORGET>reset</F-MLFFORGET> by peer
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# same as mdre-normal-other, but as failure (without <F-NOFAIL>) and [preauth] only:
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mdre-ddos-other = ^<F-MLFFORGET>(Connection (?:closed|reset)|Disconnected)</F-MLFFORGET> (?:by|from)%(__authng_user)s <HOST>%(__on_port_opt)s\s+\[preauth\]\s*$
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mdre-extra = ^Received <F-MLFFORGET>disconnect</F-MLFFORGET> from <HOST>%(__on_port_opt)s:\s*14: No(?: supported)? authentication methods available
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^Unable to negotiate with <HOST>%(__on_port_opt)s: no matching <__alg_match> found.
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^Unable to negotiate a <__alg_match>
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^no matching <__alg_match> found:
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# part of mdre-ddos-other, but user name is supplied (invalid/authenticating) on [preauth] phase only:
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mdre-extra-other = ^<F-MLFFORGET>Disconnected</F-MLFFORGET>(?: from)?(?: (?:invalid|authenticating)) user <F-USER>\S+|.*?</F-USER> <HOST>%(__on_port_opt)s \[preauth\]\s*$
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mdre-aggressive = %(mdre-ddos)s
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%(mdre-extra)s
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# mdre-extra-other is fully included within mdre-ddos-other:
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mdre-aggressive-other = %(mdre-ddos-other)s
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# Parameter "publickey": nofail (default), invalid, any, ignore
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publickey = nofail
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# consider failed publickey for invalid users only:
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cmnfailre-failed-pub-invalid = ^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 ).)*)$)
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# consider failed publickey for valid users too (don't need RE, see cmnfailed):
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cmnfailre-failed-pub-any =
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# same as invalid, but consider failed publickey for valid users too, just as no failure (helper to get IP and user-name only, see cmnfailed):
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cmnfailre-failed-pub-nofail = <cmnfailre-failed-pub-invalid>
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# don't consider failed publickey as failures (don't need RE, see cmnfailed):
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cmnfailre-failed-pub-ignore =
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cfooterre = ^<F-NOFAIL>Connection from</F-NOFAIL> <HOST>
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failregex = %(cmnfailre)s
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<mdre-<mode>>
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%(cfooterre)s
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# Parameter "mode": normal (default), ddos, extra or aggressive (combines all)
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# Usage example (for jail.local):
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# [sshd]
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# mode = extra
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# # or another jail (rewrite filter parameters of jail):
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# [sshd-aggressive]
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# filter = sshd[mode=aggressive]
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#
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mode = normal
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#filter = sshd[mode=aggressive]
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ignoreregex =
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maxlines = 1
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journalmatch = _SYSTEMD_UNIT=sshd.service + _COMM=sshd
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# DEV Notes:
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#
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# "Failed \S+ for .*? from <HOST>..." failregex uses non-greedy catch-all because
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# it is coming before use of <HOST> which is not hard-anchored at the end as well,
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# and later catch-all's could contain user-provided input, which need to be greedily
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# matched away first.
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#
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# Author: Cyril Jaquier, Yaroslav Halchenko, Petr Voralek, Daniel Black and Sergey Brester aka sebres
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# Rewritten using prefregex (and introduced "mode" parameter) by Serg G. Brester.
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