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ssh.conf: Fix disconnect "Auth fail" matching

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The regex for matching against "Auth fail" disconnect log message does
not match against current versions of ssh.  OpenSSH 5.9 introduced
privilege separation of the pre-auth process, which included
[logging through monitor.c](http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/monitor.c.diff?r1=1.113&r2=1.114)
which adds " [preauth]" to the end of each message and causes the log
level to be prepended to each message.

It also fails to match against clients which send a disconnect message
with a description that is either empty or includes a space, since this
is the content in the log message after the disconnect code, per
[packet.c:1785](http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/packet.c?annotate=1.215),
which was matched by \S+.  Although I have not observed this yet, I
couldn't find anything which would preclude it in [RFC
4253](https://tools.ietf.org/html/rfc4253#section-11.1) and since the
message is attacker-controlled it provides a way to avoid getting
banned.

This commit fixes both issues.

Signed-off-by: Kevin Locke <kevin@kevinlocke.name>
This commit is contained in:
Kevin Locke 2015-10-02 15:19:42 -07:00
parent 8311bad4ea
commit 36919d9f97
1 changed files with 1 additions and 1 deletions
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2
config/filter.d/sshd.conf
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@ -27,7 +27,7 @@ failregex = ^%(__prefix_line)s(?:error: PAM: )?[aA]uthentication (?:failure|erro
^%(__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)sReceived disconnect from <HOST>: 3: \S+: Auth fail$
^%(__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: .+ \[preauth\]$