Noticed while looking at the source (to see the point of ssh-ddos).
POSSIBLE BREAK-IN ATTEMPT - sounds scary? But keep reading
the message. It's not a login failure. It's a warning about
reverse-DNS. The login can still succeed, and if it _does_ fail,
that will be logged as normal.
<exhibit n="1">
Jul 9 05:43:00 brick sshd[18971]: Address 200.41.233.234 maps to host234.advance.com.
ar, but this does not map back to the address - POSSIBLE BREAK-IN ATTEMPT!
Jul 9 05:43:00 brick sshd[18971]: Invalid user html from 200.41.233.234
</exhibit>
The problem (in my mind) is that some users are stuck with bad dns.
The warning won't stop them from logging in. I'm pretty sure they can't
even see it. But when they exceed a threshold number of logins -
which could be all successful logins - fail2ban will trigger.
fail2ban shouldn't adding additional checks to successful logins
- it goes against the name fail2ban :)
- the first X "POSSIBLE BREAK-IN ATTEMPT"s would be permitted anyway
- if you want to ban bad DNS, the right way is PARANOID in /etc/hosts.deny
I've checked the source of OpenSSH, and this will only affect the
reverse-DNS error. (I won't be offended if you want to check
for yourself though ;)
<exhibit n="2">
$ grep -r -h -C1 'ATTEMPT' openssh-5.5p1/
logit("reverse mapping checking getaddrinfo for %.700s "
"[%s] failed - POSSIBLE BREAK-IN ATTEMPT!", name, ntop);
return xstrdup(ntop);
--
logit("Address %.100s maps to %.600s, but this does not "
"map back to the address - POSSIBLE BREAK-IN ATTEMPT!",
ntop, name);
$
</exhibit>
Based on previous work as documented in the bug by Amir and myself,
plus some enhancements and documentation added to the file itself rather
than a URL (they rot).
following commits were squashed from feature branch use_dns
commit 068c105eb5
Author: Lee Clemens <java@leeclemens.net>
Date: Tue Jan 10 22:19:04 2012 -0500
Prevent warning when IP is read from log
commit 635ed36a8c
Author: Lee Clemens <java@leeclemens.net>
Date: Tue Jan 10 22:17:08 2012 -0500
Removed logDebug
commit 24656d2812
Merge: 7957fbec429f5c
Author: Lee Clemens <java@leeclemens.net>
Date: Tue Jan 10 21:13:11 2012 -0500
Merge branch 'enh/use_dns' of github:leeclemens/fail2ban into enh/use_dns
Conflicts:
testcases/filtertestcase.py
commit 7957fbe821
Author: Lee Clemens <java@leeclemens.net>
Date: Tue Jan 10 21:09:58 2012 -0500
filtertestcase fixes from yarikoptic
commit 6ce9d04640
Author: Yaroslav Halchenko <debian@onerussian.com>
Date: Tue Jan 10 19:26:05 2012 -0500
RF: for consistency use_dns -> usedns
I guess it was might fault of inconsistency suggesting that name.
Other options/commands do not have _ in the names, so let it be
consistent with the rest for now
commit cfb2c75b49
Author: Lee Clemens <java@leeclemens.net>
Date: Tue Jan 10 19:18:41 2012 -0500
Updated DNSUtilsTests to test use_dns and added positive test to testTextToIp
commit f6186eff14
Author: Lee Clemens <java@leeclemens.net>
Date: Tue Jan 10 19:02:04 2012 -0500
Changed wording of 'DNS Reverse lookup used' message
commit 82c62d29dc
Author: Lee Clemens <java@leeclemens.net>
Date: Tue Jan 10 18:53:17 2012 -0500
Removed extraneous "n"
commit dc0ae21932
Author: Lee Clemens <java@leeclemens.net>
Date: Mon Jan 9 23:07:59 2012 -0500
ENH: use_dns - removed debugging statements
commit 594e25818c
Author: Lee Clemens <java@leeclemens.net>
Date: Mon Jan 9 22:53:39 2012 -0500
Added use_dns protocol to set and get per jail during runtime
commit 48ff80ffac
Author: Lee Clemens <java@leeclemens.net>
Date: Mon Jan 9 22:41:18 2012 -0500
Completed use_dns for initial startup - with debugging statements
commit 0bdab4c2d7
Author: Lee Clemens <java@leeclemens.net>
Date: Mon Jan 9 20:05:35 2012 -0500
ENH: Added use_dns option
commit 6d6b734ea5
Author: Lee Clemens <java@leeclemens.net>
Date: Mon Jan 9 20:01:34 2012 -0500
ENH: Added use_dns option
commit 11ad2b6125
Author: Lee Clemens <java@leeclemens.net>
Date: Mon Jan 9 19:17:30 2012 -0500
Added useDns flag to testcase
commit b48fa9b6af
Author: Lee Clemens <java@leeclemens.net>
Date: Sun Jan 8 15:13:27 2012 -0500
Added use_dns option in jail.conf
commit c429f5c91a
Merge: 4b18afb0021906
Author: leeclemens <java@leeclemens.net>
Date: Tue Jan 10 16:32:22 2012 -0800
Merge pull request #3 from yarikoptic/enh/use_dns
let's be consistent ;-)
commit 0021906358
Author: Yaroslav Halchenko <debian@onerussian.com>
Date: Tue Jan 10 19:26:05 2012 -0500
RF: for consistency use_dns -> usedns
I guess it was might fault of inconsistency suggesting that name.
Other options/commands do not have _ in the names, so let it be
consistent with the rest for now
commit 4b18afb28a
Author: Lee Clemens <java@leeclemens.net>
Date: Tue Jan 10 19:18:41 2012 -0500
Updated DNSUtilsTests to test use_dns and added positive test to testTextToIp
commit 4fae37e46f
Author: Lee Clemens <java@leeclemens.net>
Date: Tue Jan 10 19:02:04 2012 -0500
Changed wording of 'DNS Reverse lookup used' message
commit e94806ce48
Author: Lee Clemens <java@leeclemens.net>
Date: Tue Jan 10 18:53:17 2012 -0500
Removed extraneous "n"
commit 4d30c52907
Author: Lee Clemens <java@leeclemens.net>
Date: Mon Jan 9 23:07:59 2012 -0500
ENH: use_dns - removed debugging statements
commit 76696d452a
Author: Lee Clemens <java@leeclemens.net>
Date: Mon Jan 9 22:53:39 2012 -0500
Added use_dns protocol to set and get per jail during runtime
commit 0631618087
Author: Lee Clemens <java@leeclemens.net>
Date: Mon Jan 9 22:41:18 2012 -0500
Completed use_dns for initial startup - with debugging statements
commit d23d495547
Author: Lee Clemens <java@leeclemens.net>
Date: Mon Jan 9 20:05:35 2012 -0500
ENH: Added use_dns option
commit 9538553bc5
Author: Lee Clemens <java@leeclemens.net>
Date: Mon Jan 9 20:01:34 2012 -0500
ENH: Added use_dns option
commit ae1e857e53
Author: Lee Clemens <java@leeclemens.net>
Date: Mon Jan 9 19:17:30 2012 -0500
Added useDns flag to testcase
commit ace43eb941
Author: Lee Clemens <java@leeclemens.net>
Date: Sun Jan 8 15:13:27 2012 -0500
Added use_dns option in jail.conf
According to rfc2822, Date: headers are not optional.
Added these to all sendmail action templates, format specification
should conform to rfc and be portable across multiple platforms.
e.g.
Sep 25 12:51:04 myhost kernel: [773580.832329] sshd[25557]: Invalid user pgsql from 91.203.223.206
This fixes the sshd filter on Fedora 15, and probably other filters on
other newish distros too.
Yaroslav Halchenko