fail2ban not working with SSHD

Petrushka asked:

I am running fail2ban (0.9.6-2) on Debian 9 with busybox-syslogd logging to /var/log/auth.log
setup with the following line in /etc/rc.local to get logs written to file.

/sbin/syslogd -O /var/log/auth.log || exit 1

SSHD jail is enabled but does not see failed login attempts

running fail2ban-regex on the auth.log file with the sshd filter gives no fails.

sshd_config set to AUTHPRIV and VERBOSE

Here is a sample of auth.log logs:

   Jan 14 17:12:41 Fire-Video authpriv.info sshd[2556]: Failed none for video from 192.168.60.5 port 56068 ssh2
Jan 14 17:12:42 Fire-Video authpriv.info sshd[2556]: Failed password for video from 192.168.60.5 port 56068 ssh2
Jan 14 17:12:42 Fire-Video authpriv.info sshd[2556]: Failed password for video from 192.168.60.5 port 56068 ssh2
Jan 14 17:12:42 Fire-Video authpriv.info sshd[2556]: Connection closed by 192.168.60.5 port 56068 [preauth]
Jan 14 17:12:49 Fire-Video authpriv.info sshd[2558]: Connection from 192.168.60.5 port 56074 on 192.168.40.19 port 22
Jan 14 17:12:53 Fire-Video authpriv.debug sshd[2558]: pam_usermapper(sshd:auth): pam_sm_authenticate flags: 00000001
Jan 14 17:12:53 Fire-Video authpriv.notice sshd[2558]: pam_usermapper(sshd:auth): aliasing to 'root'
Jan 14 17:12:53 Fire-Video authpriv.notice sshd[2558]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=192.168.60.5  user=root
Jan 14 17:12:55 Fire-Video authpriv.info sshd[2558]: Failed password for video from 192.168.60.5 port 56074 ssh2
Jan 14 17:13:15 Fire-Video authpriv.debug sshd[2558]: pam_usermapper(sshd:auth): pam_sm_authenticate flags: 00000001
Jan 14 17:13:16 Fire-Video authpriv.info sshd[2558]: Failed password for video from 192.168.60.5 port 56074 ssh2
Jan 14 17:13:21 Fire-Video authpriv.debug sshd[2558]: pam_usermapper(sshd:auth): pam_sm_authenticate flags: 00000001
Jan 14 17:13:21 Fire-Video authpriv.info sshd[2558]: Accepted password for video from 192.168.60.5 port 56074 ssh2
Jan 14 17:13:21 Fire-Video authpriv.info sshd[2558]: pam_unix(sshd:session): session opened for user root by (uid=0)

This is my sshd.conf in filter.d

      # 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
    
    [Definition]
    
    _daemon = sshd
    
    failregex = ^%(__prefix_line)s(?:error: PAM: )?[aA]uthentication (?:failure|error|failed) for .* from <HOST>( via \S+)?\s*$
                ^%(__prefix_line)s(?:error: PAM: )?User not known to the underlying authentication module for .* from <HOST>\s*$
                ^%(__prefix_line)sFailed \S+ for (?P<cond_inv>invalid user )?(?P<user>(?P<cond_user>\S+)|(?(cond_inv)(?:(?! from ).)*?|[^:]+)) from <HOST>(?: port \d+)?(?: ssh\d*)?(?(cond_user):|(?:(?:(?! from ).)*)$)
                ^%(__prefix_line)sROOT LOGIN REFUSED.* FROM <HOST>\s*$
                ^%(__prefix_line)s[iI](?:llegal|nvalid) user .*? from <HOST>(?: port \d+)?\s*$
                ^%(__prefix_line)sUser .+ from <HOST> not allowed because not listed in AllowUsers\s*$
                ^%(__prefix_line)sUser .+ from <HOST> not allowed because listed in DenyUsers\s*$
                ^%(__prefix_line)sUser .+ from <HOST> not allowed because not in any group\s*$
                ^%(__prefix_line)srefused connect from \S+ \(<HOST>\)\s*$
                ^%(__prefix_line)s(?:error: )?Received disconnect from <HOST>: 3: .*: Auth fail(?: \[preauth\])?$
                ^%(__prefix_line)sUser .+ from <HOST> not allowed because a group is listed in DenyGroups\s*$
                ^%(__prefix_line)sUser .+ from <HOST> not allowed because none of user's groups are listed in AllowGroups\s*$
                ^(?P<__prefix>%(__prefix_line)s)User .+ not allowed because account is locked<SKIPLINES>(?P=__prefix)(?:error: )?Received disconnect from <HOST>: 11: .+ \[preauth\]$
                ^(?P<__prefix>%(__prefix_line)s)Disconnecting: Too many authentication failures for .+? \[preauth\]<SKIPLINES>(?P=__prefix)(?:error: )?Connection closed by <HOST> \[preauth\]$
                ^(?P<__prefix>%(__prefix_line)s)Connection from <HOST> port \d+(?: on \S+ port \d+)?<SKIPLINES>(?P=__prefix)Disconnecting: Too many authentication failures for .+? \[preauth\]$
                ^%(__prefix_line)s(error: )?maximum authentication attempts exceeded for .* from <HOST>(?: port \d*)?(?: ssh\d*)? \[preauth\]$
                ^%(__prefix_line)spam_unix\(sshd:auth\):\s+authentication failure;\s*logname=\S*\s*uid=\d*\s*euid=\d*\s*tty=\S*\s*ruser=\S*\s*rhost=<HOST>\s.*$
    
    ignoreregex = 
    
    [Init]
    
    # "maxlines" is number of log lines to buffer for multi-line regex searches
    maxlines = 10
    
    journalmatch = _SYSTEMD_UNIT=sshd.service + _COMM=sshd

# 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

My answer:


The problem with all of these is that the __prefix_line does not match busybox syslogd’s strange log format. Thus fail2ban cannot make sense of any log entry created by busybox.

You can try to use the -S option to cause busybox syslogd to use an abbreviated log format that should match the __prefix_line but is less useful as a general log.

/sbin/syslogd -S -O /var/log/auth.log || exit 1

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