# 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 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 # 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: __authng_user = (?: (?:invalid|authenticating) user \S+|.+?)? # 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 = ^%(__prefix_line)s%(__pref)s.+$ cmnfailre = ^[aA]uthentication (?:failure|error|failed) for .* from ( via \S+)?%(__suff)s$ ^User not known to the underlying authentication module for .* from %(__suff)s$ > ^Failed for (?Pinvalid user )?(?P\S+)|(?(cond_inv)(?:(?! from ).)*?|[^:]+) from %(__on_port_opt)s(?: ssh\d*)?(?(cond_user): |(?:(?:(?! from ).)*)$) ^ROOT LOGIN REFUSED FROM ^[iI](?:llegal|nvalid) user .*? from %(__suff)s$ ^User .+ from not allowed because not listed in AllowUsers%(__suff)s$ ^User .+ from not allowed because listed in DenyUsers%(__suff)s$ ^User .+ from not allowed because not in any group%(__suff)s$ ^refused connect from \S+ \(\) ^Received disconnect from %(__on_port_opt)s:\s*3: .*: Auth fail%(__suff)s$ ^User .+ from not allowed because a group is listed in DenyGroups%(__suff)s$ ^User .+ from not allowed because none of user's groups are listed in AllowGroups%(__suff)s$ ^%(__pam_auth)s\(sshd:auth\):\s+authentication failure;(?:\s+(?:(?:logname|e?uid|tty)=\S*)){0,4}\s+ruser=\S*\s+rhost=(?:\s+user=\S*)?%(__suff)s$ ^maximum authentication attempts exceeded for .* from %(__on_port_opt)s(?: ssh\d*)?%(__suff)s$ ^User .+ not allowed because account is locked%(__suff)s ^Disconnecting(?: from)?(?: (?:invalid|authenticating)) user \S+ %(__on_port_opt)s:\s*Change of username or service not allowed:\s*.*\[preauth\]\s*$ ^Disconnecting: Too many authentication failures(?: for .+?)?%(__suff)s$ ^Received disconnect from %(__on_port_opt)s:\s*11: -other> ^Accepted \w+ for \S+ from (?:\s|$) cmnfailed-any = \S+ cmnfailed-ignore = \b(?!publickey)\S+ cmnfailed-invalid = cmnfailed-nofail = (?:publickey|\S+) cmnfailed = > mdre-normal = # used to differentiate "connection closed" with and without `[preauth]` (fail/nofail cases in ddos mode) mdre-normal-other = ^(Connection closed|Disconnected) (?:by|from)%(__authng_user)s (?:%(__suff)s|\s*)$ mdre-ddos = ^Did not receive identification string from ^kex_exchange_identification: client sent invalid protocol identifier ^Bad protocol version identification '.*' from ^SSH: Server;Ltype: (?:Authname|Version|Kex);Remote: -\d+;[A-Z]\w+: ^Read from socket failed: Connection reset by peer # same as mdre-normal-other, but as failure (without ) and [preauth] only: mdre-ddos-other = ^(Connection (?:closed|reset)|Disconnected) (?:by|from)%(__authng_user)s %(__on_port_opt)s\s+\[preauth\]\s*$ mdre-extra = ^Received disconnect from %(__on_port_opt)s:\s*14: No(?: supported)? authentication methods available ^Unable to negotiate with %(__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 = ^Disconnected(?: from)?(?: (?:invalid|authenticating)) user \S+|.*? %(__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 (?P\S+)|(?:(?! from ).)*? from %(__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 = # don't consider failed publickey as failures (don't need RE, see cmnfailed): cmnfailre-failed-pub-ignore = cfooterre = ^Connection from failregex = %(cmnfailre)s > %(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 # DEV Notes: # # "Failed \S+ for .*? from ..." failregex uses non-greedy catch-all because # it is coming before use of 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.