4

I'm trying to get Fail2Ban to work with the SSHD config provided.

When I run: 

fail2ban-regex /var/log/auth.log /etc/fail2ban/filter.d/sshd.conf

The output is:

root@fw:/etc/fail2ban/filter.d# fail2ban-regex /var/log/auth.log /etc/fail2ban/filter.d/sshd.conf

Running tests
=============

Use   failregex file : /etc/fail2ban/filter.d/sshd.conf
Use         log file : /var/log/auth.log


Results
=======

Failregex: 5583 total
|-  #) [# of hits] regular expression
|   3) [4339] ^\s*(<[^.]+\.[^.]+>)?\s*(?:\S+ )?(?:kernel: \[\d+\.\d+\] )?(?:@vserver_\S+ )?(?:(?:\[\d+\])?:\s+[\[\(]?sshd(?:\(\S+\))?[\]\)]?:?|[\[\(]?sshd(?:\(\S+\))?[\]\)]?:?(?:\[\d+\])?:?)?\s(?:\[ID \d+ \S+\])?\s*Failed \S+ for .*? from <HOST>(?: port \d*)?(?: ssh\d*)?(: (ruser .*|(\S+ ID \S+ \(serial \d+\) CA )?\S+ (?:[\da-f]{2}:){15}[\da-f]{2}(, client user ".*", client host ".*")?))?\s*$
|   5) [1244] ^\s*(<[^.]+\.[^.]+>)?\s*(?:\S+ )?(?:kernel: \[\d+\.\d+\] )?(?:@vserver_\S+ )?(?:(?:\[\d+\])?:\s+[\[\(]?sshd(?:\(\S+\))?[\]\)]?:?|[\[\(]?sshd(?:\(\S+\))?[\]\)]?:?(?:\[\d+\])?:?)?\s(?:\[ID \d+ \S+\])?\s*[iI](?:llegal|nvalid) user .* from <HOST>\s*$
`-

Ignoreregex: 0 total

Date template hits:
|- [# of hits] date format
|  [19480] MONTH Day Hour:Minute:Second
`-

Lines: 19480 lines, 0 ignored, 5583 matched, 13897 missed
Missed line(s):: too many to print.  Use --print-all-missed to print all 13897 lines
root@fw:/etc/fail2ban/filter.d#

My auth.log looks like this (sample):

Oct 21 04:47:44 fw sshd[31558]: Disconnecting: Too many authentication failures for root [preauth]
Oct 21 04:47:44 fw sshd[31558]: PAM 5 more authentication failures; logname= uid=0 euid=0 tty=ssh ruser= rhost=218.2.0.125  user=root
Oct 21 04:47:44 fw sshd[31558]: PAM service(sshd) ignoring max retries; 6 > 3
Oct 21 04:47:46 fw sshd[31562]: Failed password for root from 218.2.0.125 port 12277 ssh2
Oct 21 04:47:46 fw sshd[31581]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=218.2.0.125  user=root
Oct 21 04:47:48 fw sshd[31560]: message repeated 5 times: [ Failed password for root from 218.2.0.125 port 9188 ssh2]
Oct 21 04:47:48 fw sshd[31560]: Disconnecting: Too many authentication failures for root [preauth]
Oct 21 04:47:48 fw sshd[31560]: PAM 5 more authentication failures; logname= uid=0 euid=0 tty=ssh ruser= rhost=218.2.0.125  user=root
Oct 21 04:47:48 fw sshd[31560]: PAM service(sshd) ignoring max retries; 6 > 3
Oct 21 04:47:48 fw sshd[31581]: Failed password for root from 218.2.0.125 port 13148 ssh2
Oct 21 04:47:52 fw sshd[31595]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=218.2.0.125  user=root
Oct 21 04:47:55 fw sshd[31595]: Failed password for root from 218.2.0.125 port 14409 ssh2
Oct 21 04:47:55 fw CRON[31494]: pam_unix(cron:session): session closed for user clamav
Oct 21 04:47:59 fw sshd[31562]: message repeated 5 times: [ Failed password for root from 218.2.0.125 port 12277 ssh2]
Oct 21 04:47:59 fw sshd[31562]: Disconnecting: Too many authentication failures for root [preauth]
Oct 21 04:47:59 fw sshd[31562]: PAM 5 more authentication failures; logname= uid=0 euid=0 tty=ssh ruser= rhost=218.2.0.125  user=root
Oct 21 04:47:59 fw sshd[31562]: PAM service(sshd) ignoring max retries; 6 > 3
Oct 21 04:47:59 fw sshd[31581]: message repeated 5 times: [ Failed password for root from 218.2.0.125 port 13148 ssh2]
Oct 21 04:47:59 fw sshd[31581]: Disconnecting: Too many authentication failures for root [preauth]
Oct 21 04:47:59 fw sshd[31581]: fatal: Write failed: Connection reset by peer [preauth]
Oct 21 04:47:59 fw sshd[31581]: PAM 5 more authentication failures; logname= uid=0 euid=0 tty=ssh ruser= rhost=218.2.0.125  user=root
Oct 21 04:47:59 fw sshd[31581]: PAM service(sshd) ignoring max retries; 6 > 3
Oct 21 04:48:00 fw sshd[31595]: message repeated 2 times: [ Failed password for root from 218.2.0.125 port 14409 ssh2]

I know that there are entries that should match, but I just can't get it to match.

After researching, I've found that it may be down to the date format, but suggested changes to the common.conf didn't make any difference.

Also, I ran a manual fail2ban-regex with the date format of auth.log and it returned as expected.

mickmackusa
  • 852
  • 1
  • 9
  • 18
Matt Wood
  • 41
  • 1
  • 3

2 Answers2

4

It looks like there are matches, but not enough. Debian bug #620364 is probably to blame. The workaround, documented on the fail2ban wiki and Stack Overflow, is to turn off repeated message reduction in rsyslog:

sudo sed -i 's/RepeatedMsgReduction\ on/RepeatedMsgReduction\ off/' /etc/rsyslog.conf
sudo service rsyslog restart
sudo service fail2ban restart
Community
  • 1
Mihai Capotă
  • 2,158
  • 1
  • 20
  • 23
0
Failed password for root

Is correctly matches against the 3rd entry in the fail2ban filter for ssh and was corrected https://github.com/fail2ban/fail2ban/commit/750e0c1e3dbce856437c115142d57f18b6c1fac7.

message repeated 5 times

Is a consequence of the duplicated messages which is fixed as per the syslog changes (and doesn't require fail2ban restart).

PAM 5....

Could be matched however this would be a duplicate of the first "Failed Password.." log messages and there is no point.

If you come across something you need a regex for:

fail2ban-regex -D 'log line' /etc/fail2ban/filter.d/sshd.conf

And use the URLs near the regex that it should match and edit that until it matches.

danblack
  • 1