Difference between revisions of "Coping With Postfix Mail Server Attacks"
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You're going to see a lot of forged addresses. In this example, HawaiiVacationDeals@eiroeir.eu is clearly forged. | You're going to see a lot of forged addresses. In this example, HawaiiVacationDeals@eiroeir.eu is clearly forged. | ||
| − | + | ==== DETERMINE SENDER SOURCE ==== | |
| − | + | ||
| − | + | ||
It is possible that your own server is the source. This is possible in a couple different ways: | It is possible that your own server is the source. This is possible in a couple different ways: | ||
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postcat -vq 9AFA82C0499 | postcat -vq 9AFA82C0499 | ||
| − | + | ==== SCENARIO: Local User account compromised or sending spam from compromised system ==== | |
| + | |||
| + | If you grep for the message ID (9AFA82C0499in in our example) within /var/log/mail.log you should find a log line indicating the sasl_username. With that username you can see just how much spam the account is responsible for attempting to send or sending: | ||
| + | cat /var/log/maillog|grep <username> | ||
| + | |||
| + | Disable the account | ||
| + | passwd -l <username> | ||
| − | + | Block the IP address of the account. The user may have a dynamic IP address. Consider this a temporary measure just to get things under control. At some point the user is going to attempt to contact you because his or her mail is no longer working. You can do this using IPTABLES. | |
| − | + | There may continue to be much activity for a duration because all of the remote hosts your server was trying to send spam to will continue to send bounce replies. | |
Revision as of 09:34, 9 April 2015
There are a number of different attacks possible. You might encounter a Brute Force Dictionary Attack on Dovecot or a basic mail relay attack. Those are only two common examples out of many possibilities. This article deals with relay attacks.
Related / See Also:
- Postfix Tips and Tricks
- Postfix Help
- Brute Force Dictionary Attack on Dovecot
- Block SMTP Authentication Attacks With Fail2Ban
- Fail2Ban
Contents
Mail Relay Attack
Assuming you are _not_ running an open relay, there are attacks which may seek to verify the relay or to attempt delivery to local users.
Too many "smtp -t unix -u" processes
1005 ? S 0:00 smtp -t unix -u 1006 ? S 0:00 smtp -t unix -u 1007 ? S 0:00 smtp -t unix -u 1008 ? S 0:00 smtp -t unix -u 1009 ? S 0:00 smtp -t unix -u 1010 ? S 0:00 smtp -t unix -u 1011 ? S 0:00 smtp -t unix -u 1012 ? S 0:00 smtp -t unix -u 1013 ? S 0:00 smtp -t unix -u 1014 ? S 0:00 smtp -t unix -u 1015 ? S 0:00 smtp -t unix -u 1016 ? S 0:00 smtp -t unix -u 1017 ? S 0:00 smtp -t unix -u 1018 ? S 0:00 smtp -t unix -u 1019 ? S 0:00 smtp -t unix -u 1020 ? S 0:00 smtp -t unix -u 1021 ? S 0:00 smtp -t unix -u 1022 ? S 0:00 bounce -z -n defer -t unix -u 1023 ? S 0:00 smtp -t unix -u 1024 ? S 0:00 smtp -t unix -u 1025 ? S 0:00 smtp -t unix -u 1026 ? S 0:00 smtp -t unix -u 1027 ? S 0:00 smtp -t unix -u 1028 ? S 0:00 smtp -t unix -u 1030 ? S 0:00 smtp -t unix -u 1031 ? S 0:00 smtp -t unix -u 1032 ? S 0:00 smtp -t unix -u 1033 ? S 0:00 smtp -t unix -u 1034 ? S 0:00 smtp -t unix -u 1035 ? S 0:00 smtp -t unix -u 1036 ? S 0:00 smtp -t unix -u 1038 ? S 0:00 dovecot/pop3-login
Someone is attacking your email server. The server is spawning too many smtp processes and is slow or nearly not responsive.
Lets verify. Check the mail queue using either 'postqueue -p' or 'mailq' command.
mailq
You can find a lot of useful commands like mailq in our Postfix Tips and Tricks page.
You might see lots of entries that look similar to this:
4790F2C0DD7 2898 Mon Apr 6 13:08:07 MAILER-DAEMON
(connect to bny234.rayinsuranceclearly.ninja[94.228.216.234]:25: Connection timed out)
Angela.Sloan@bny234.rayinsuranceclearly.ninja
They might say "Connection timed out" or "Connection refused"
437AC2C07BB 9359 Tue Apr 7 18:05:33 MAILER-DAEMON
(connect to 1fxxn8s.eiroeir.eu[8.39.223.104]:25: Connection refused)
HawaiiVacationDeals@eiroeir.eu
You're going to see a lot of forged addresses. In this example, HawaiiVacationDeals@eiroeir.eu is clearly forged.
DETERMINE SENDER SOURCE
It is possible that your own server is the source. This is possible in a couple different ways:
- You have a Perl or PHP script or something similar that is being exploited and used to relay spam
- You have a system user that has had their account compromised
It is also possible that an external source is trying to relay mail though your mail server.
Take a look at the mail queue
mailq
Use postcat to start going through the mail in the queue based on Queue ID. For example, if the ID is '9AFA82C0499'
postcat -vq 9AFA82C0499
SCENARIO: Local User account compromised or sending spam from compromised system
If you grep for the message ID (9AFA82C0499in in our example) within /var/log/mail.log you should find a log line indicating the sasl_username. With that username you can see just how much spam the account is responsible for attempting to send or sending:
cat /var/log/maillog|grep <username>
Disable the account
passwd -l <username>
Block the IP address of the account. The user may have a dynamic IP address. Consider this a temporary measure just to get things under control. At some point the user is going to attempt to contact you because his or her mail is no longer working. You can do this using IPTABLES.
There may continue to be much activity for a duration because all of the remote hosts your server was trying to send spam to will continue to send bounce replies.
