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Editing: sshd.conf
# Fail2Ban filter for openssh # # If you want to protect OpenSSH from being bruteforced by password # authentication then get public key authentication working before disabling # PasswordAuthentication in sshd_config. # # # "Connection from <HOST> port \d+" requires LogLevel VERBOSE in sshd_config # [INCLUDES] # Read common prefixes. If any customizations available -- read them from # common.local before = common.conf [DEFAULT] _daemon = sshd(?:-session)? # optional prefix (logged from several ssh versions) like "error: ", "error: PAM: " or "fatal: " __pref = (?:(?:error|fatal): (?:PAM: )?)? # optional suffix (logged from several ssh versions) like " [preauth]" #__suff = (?: port \d+)?(?: \[preauth\])?\s* __suff = (?: (?:port \d+|on \S+|\[preauth\])){0,3}\s* __on_port_opt = (?: (?:port \d+|on \S+)){0,2} # close by authenticating user (don't use <HOST> after %(__authng_user)s because of catch-all `.*?`): __authng_user = (?: (?:by|from))?(?: (?:invalid|authenticating) user <F-USER>\S+|.*?</F-USER>)?(?: from)? # for all possible (also future) forms of "no matching (cipher|mac|MAC|compression method|key exchange method|host key type) found", # see ssherr.c for all possible SSH_ERR_..._ALG_MATCH errors. __alg_match = (?:(?:\w+ (?!found\b)){0,2}\w+) # PAM authentication mechanism, can be overridden, e. g. `filter = sshd[__pam_auth='pam_ldap']`: __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$ <cmnfailre-failed-pub-<publickey>> ^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 ).)*)$) ^<F-USER>ROOT</F-USER> LOGIN REFUSED FROM <HOST> ^[iI](?:llegal|nvalid) user <F-USER>.*?</F-USER> (?:from )?<HOST>%(__suff)s$ ^User <F-USER>\S+|.*?</F-USER> (?:from )?<HOST> not allowed because not listed in AllowUsers%(__suff)s$ ^User <F-USER>\S+|.*?</F-USER> (?:from )?<HOST> not allowed because listed in DenyUsers%(__suff)s$ ^User <F-USER>\S+|.*?</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>\S+|.*?</F-USER> (?:from )?<HOST> not allowed because a group is listed in DenyGroups%(__suff)s$ ^User <F-USER>\S+|.*?</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$ ^maximum authentication attempts exceeded for (?:invalid user )?<F-USER>.*?</F-USER> (?:from )?<HOST>%(__on_port_opt)s(?: ssh\d*)?%(__suff)s$ ^User <F-USER>\S+|.*?</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*$ ^Disconnecting: Too many authentication failures(?: for <F-USER>\S+|.*?</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|$) cmnfailed-any = \S+ cmnfailed-ignore = \b(?!publickey)\S+ cmnfailed-invalid = <cmnfailed-ignore> cmnfailed-nofail = (?:<F-NOFAIL>publickey</F-NOFAIL>|\S+) cmnfailed = <cmnfailed-<publickey>> mdre-normal = # used to differentiate "connection closed" with and without `[preauth]` (fail/nofail cases in ddos mode) mdre-normal-other = ^<F-NOFAIL><F-MLFFORGET>(?:Connection (?:closed|reset)|Disconnect(?:ed|ing))</F-MLFFORGET></F-NOFAIL>%(__authng_user)s <ADDR>%(__on_port_opt)s(?:: (?!Too many authentication failures)[^\[]+)?(?: \[preauth\])?\s*$ mdre-ddos = ^(?:Did not receive identification string from|Timeout before authentication for) <HOST> ^kex_exchange_identification: (?:read: )?(?:[Cc]lient sent invalid protocol identifier|[Cc]onnection (?:closed by remote host|reset by peer)) ^Bad protocol version identification '(?:[^']|.*?)' (?:from )?<HOST>%(__suff)s$ ^<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 ^(?:banner exchange|ssh_dispatch_run_fatal): Connection from <HOST><__on_port_opt>: (?:invalid format|(?:message authentication code incorrect|[Cc]onnection corrupted) \[preauth\]) # same as mdre-normal-other, but as failure (without <F-NOFAIL> with [preauth] and with <F-NOFAIL> on no preauth phase as helper to identify address): mdre-ddos-other = ^<F-MLFFORGET>(?:Connection (?:closed|reset)|Disconnect(?:ed|ing))</F-MLFFORGET>%(__authng_user)s <ADDR>%(__on_port_opt)s(?:: (?!Too many authentication failures)[^\[]+)?\s+\[preauth\]\s*$ ^<F-NOFAIL><F-MLFFORGET>(?:Connection (?:closed|reset)|Disconnect(?:ed|ing))</F-MLFFORGET></F-NOFAIL>%(__authng_user)s <ADDR>(?:%(__on_port_opt)s(?:: (?!Too many authentication failures)[^\[]+)?|\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: # part of mdre-ddos-other, but user name is supplied (invalid/authenticating) on [preauth] phase only: mdre-extra-other = ^<F-MLFFORGET>Disconnected</F-MLFFORGET>(?: from)?(?: (?:invalid|authenticating)) user <F-USER>\S+|.*?</F-USER> (?:from )?<HOST>%(__on_port_opt)s \[preauth\]\s*$ mdre-aggressive = %(mdre-ddos)s %(mdre-extra)s # mdre-extra-other is fully included within mdre-ddos-other: mdre-aggressive-other = %(mdre-ddos-other)s # Parameter "publickey": nofail (default), invalid, any, ignore publickey = nofail # consider failed publickey for invalid users only: 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 ).)*)$) # consider failed publickey for valid users too (don't need RE, see cmnfailed): cmnfailre-failed-pub-any = # 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): cmnfailre-failed-pub-nofail = <cmnfailre-failed-pub-invalid> # don't consider failed publickey as failures (don't need RE, see cmnfailed): cmnfailre-failed-pub-ignore = cfooterre = ^<F-NOFAIL>Connection from</F-NOFAIL> <HOST> failregex = %(cmnfailre)s <mdre-<mode>> %(cfooterre)s # Parameter "mode": normal (default), ddos, extra or aggressive (combines all) # Usage example (for jail.local): # [sshd] # mode = extra # # or another jail (rewrite filter parameters of jail): # [sshd-aggressive] # filter = sshd[mode=aggressive] # mode = normal #filter = sshd[mode=aggressive] ignoreregex = maxlines = 1 journalmatch = _SYSTEMD_UNIT=sshd.service + _COMM=sshd + _COMM=sshd-session # DEV Notes: # # "Failed \S+ for .*? from <HOST>..." failregex uses non-greedy catch-all because # it is coming before use of <HOST> which is not hard-anchored at the end as well, # and later catch-all's could contain user-provided input, which need to be greedily # matched away first. # # Author: Cyril Jaquier, Yaroslav Halchenko, Petr Voralek, Daniel Black and Sergey Brester aka sebres # Rewritten using prefregex (and introduced "mode" parameter) by Serg G. Brester.
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