Logs and how to read them
Rick Stevens
rstevens at vitalstream.com
Wed Apr 21 20:56:36 UTC 2004
Mike Rambour wrote:
> I am a very newbie here and my ISP is saying they received a
> complaint about SPAM being sent from my machine, they claim its my IP
> that sent it (fixed IP, not DHCP).
>
> I have checked and I have relaying turned off and only 6 valid users
> on the machine, I forced a password change for all accounts. I also
> used Abuse.Nets relay test to make sure I was not allowing relays. I
> have no idea how that SPAM got out. Since this machine is a firewall
> for our office, I tested all internal machines for virus/worms/etc with
> the latest tools.
Are these Windows machines, by any chance? Are you sure they don't have
a Bagel or Klez virus?
> So, in the process I looked at all my logs in /var/log I specifically
> grep'd for the email address that the spam was sent as and to and found
> no references to it in my logs implying it was not my machine. But I
> found other things that I dont know how to read.
Such as? The logs you are interested in are (predominately)
/var/log/messages
/var/log/maillog
/var/log/dmesg (well, you really don't need that one)
> I googled and found no place for a "how-to read logs and what they
> mean". In /var/log/messages, I googled for "lame servers" and found
> that is ok along with a few other items.
>
> in maillog however, I see very few "Relaying denied" messages (I
> expected more of them) and a lot of "lost input" messages that from
> googling appears to be a spammer that got blocked and ok (is that
> true?). In every case where a "lost input" was I could find 2 lines,
> one for the "from" and one for lost input with the matching
> "sendmail[xxxx]" number.
That sounds right.
>
> But lines like these 2 below did NOT have matching lines, does this
> mean they got sent ? relayed thru my machine somehow ? I could not find
> a fail or sent line for many lines like the ones below.
>
> Apr 21 12:25:00 mail sendmail[1067]: MAA01067:
> from=<postmaster at hoteiscontinental.com.br>, size=1657, class=0, pri=0
> , nrcpts=0, proto=ESMTP, relay=[200.213.72.130]
That looks like a relay attempt. The sending system's IP was
200.213.72.130. Look for another entry with that same "sendmail[1067]"
bit, and you'll see the delivery attempt.
> Apr 21 12:29:03 mail sendmail[1214]: MAA01214: from=<>, size=0, class=0,
> pri=0, nrcpts=0, proto=SMTP, relay=fw1-81-80-126-2.bplc.fr [81.80.126.2]
That's also a relay attempt. Look for another entry with
"sendmail[1214]" in it to see the delivery attempt. BTW, that's one of
the classic spammer ploys...using "<>" as the sending address. Your
sendmail.cf should catch that and not relay it.
You should go to sendmail.org's site and read up on anti-spam and anti-
relay setups. Also make sure you have current sendmail binaries
installed.
----------------------------------------------------------------------
- Rick Stevens, Senior Systems Engineer rstevens at vitalstream.com -
- VitalStream, Inc. http://www.vitalstream.com -
- -
- Artificial Intelligence usually beats real stupidity. -
----------------------------------------------------------------------
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