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luri
Asked: 2011-05-18 10:22:55 +0800 CST

Fail2ban misses some relay attempts

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I have some relay attempts like these in my mail.log (they total 281 connection attempts in less than 3 minutes):

May 16 04:58:30 MyServer postfix/smtpd[18950]: connect from unknown[xx.yy.zzz.www]
May 16 04:58:30 MyServer postfix/smtpd[18951]: warning: xx.yy.zzz.www: hostname xx-yy-zzz-www.network.domain verification failed: No address associated with hostname
May 16 04:58:30 MyServer postfix/smtpd[18951]: connect from unknown[xx.yy.zzz.www]
May 16 04:58:31 MyServer postfix/smtpd[18947]: warning: unknown[xx.yy.zzz.www]: SASL LOGIN authentication failed: authentication failure
May 16 04:58:31 MyServer postfix/smtpd[18952]: warning: xx.yy.zzz.www: hostname xx-yy-zzz-www.network.domain verification failed: No address associated with hostname
May 16 04:58:31 MyServer postfix/smtpd[18952]: connect from unknown[xx.yy.zzz.www]
May 16 04:58:31 MyServer postfix/smtpd[18947]: disconnect from unknown[xx.yy.zzz.www]
May 16 04:58:32 MyServer postfix/smtpd[18922]: warning: unknown[xx.yy.zzz.www]: SASL LOGIN authentication failed: authentication failure
May 16 04:58:32 MyServer postfix/smtpd[18947]: warning: xx.yy.zzz.www: hostname xx-yy-zzz-www.network.domain verification failed: No address associated with hostname
May 16 04:58:32 MyServer postfix/smtpd[18947]: connect from unknown[xx.yy.zzz.www]
May 16 04:58:33 MyServer postfix/smtpd[18953]: warning: xx.yy.zzz.www: hostname xx-yy-zzz-www.network.domain verification failed: No address associated with hostname
May 16 04:58:33 MyServer postfix/smtpd[18953]: connect from unknown[xx.yy.zzz.www]
May 16 04:58:33 MyServer postfix/smtpd[18922]: disconnect from unknown[xx.yy.zzz.www]
May 16 04:58:33 MyServer postfix/smtpd[18948]: warning: unknown[xx.yy.zzz.www]: SASL LOGIN authentication failed: authentication failure
May 16 04:58:33 MyServer postfix/smtpd[18949]: warning: unknown[xx.yy.zzz.www]: SASL LOGIN authentication failed: authentication failure
May 16 04:58:33 MyServer postfix/smtpd[18922]: warning: xx.yy.zzz.www: hostname xx-yy-zzz-www.network.domain verification failed: No address associated with hostname
May 16 04:58:33 MyServer postfix/smtpd[18922]: connect from unknown[xx.yy.zzz.www]
May 16 04:58:34 MyServer postfix/smtpd[18948]: disconnect from unknown[xx.yy.zzz.www]
May 16 04:58:34 MyServer postfix/smtpd[18949]: disconnect from unknown[xx.yy.zzz.www]
May 16 04:58:34 MyServer postfix/smtpd[18948]: warning: xx.yy.zzz.www: hostname xx-yy-zzz-www.network.domain verification failed: No address associated with hostname
May 16 04:58:34 MyServer postfix/smtpd[18948]: connect from unknown[xx.yy.zzz.www]
May 16 04:58:34 MyServer postfix/smtpd[18949]: warning: xx.yy.zzz.www: hostname xx-yy-zzz-www.network.domain verification failed: No address associated with hostname
May 16 04:58:34 MyServer postfix/smtpd[18949]: connect from unknown[xx.yy.zzz.www]
May 16 04:58:35 MyServer postfix/smtpd[18950]: warning: unknown[xx.yy.zzz.www]: SASL LOGIN authentication failed: authentication failure
May 16 04:58:35 MyServer postfix/smtpd[18951]: warning: unknown[xx.yy.zzz.www]: SASL LOGIN authentication failed: authentication failure
May 16 04:58:35 MyServer postfix/smtpd[18950]: disconnect from unknown[xx.yy.zzz.www]

I guess filter sasl (which is enabled) should take care of them, but ip is never banned. Seems there's no match with the failregex expression in sasl.conf filter:

# Fail2Ban configuration file
#
# Author: Yaroslav Halchenko
#
# $Revision: 728 $
#

[Definition]

# Option: failregex
# Notes.: regex to match the password failures messages in the logfile. The
#          host must be matched by a group named "host". The tag "<HOST>" can
#          be used for standard IP/hostname matching and is only an alias for
#          (?:::f{4,6}:)?(?P<host>[\w\-.^_]+)
# Values: TEXT
#
failregex = (?i): warning: [-._\w]+\[<HOST>\]: SASL (?:LOGIN|PLAIN|(?:CRAM|DIGEST)-MD5) authentication failed(: [A-Za-z0-9+/]*={0,2})?$

# Option:  ignoreregex
# Notes.:  regex to ignore. If this regex matches, the line is ignored.
# Values:  TEXT
#
ignoreregex =

Any hint on what's failing here? Any way to correct the problem?

Edit: A simpler question that could be a start for troubleshooting this issue: do those SASL LOGIN warnings in mail.log match the failregex expression? I don't really know how to test it, and I don't have enough knowledge about regex sintax to work it out on my own.

Thanks in advance.

fail2ban

1 Answers

  1. Best Answer

    The last part of the regex does not match "authentication failure"

    The failing part of the regex seems to match a base64 string:

    (: [A-Za-z0-9+/]*={0,2})?*={0,2})?

    Since "authentication failure" should definitely be blocked, I suggest replacing that part of the regex with:

    (: ([A-Za-z0-9+/]*={0,2})?*={0,2})|authentication failure)?

    This is an addition to the old rule, and would match : authentication failure.

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