Knowledge Base

How to identify spam source on Plesk for Linux Server

Question

Many email messages are being sent from PHP scripts on a server. How to find domains on which these scripts are running if Postfix is used?

Answer

Warning: if you do not have SSH access contact your service provider or server administrator.

Note: This article is applicable to the Postfix mail server only.

There is a way to determine from which directory the PHP script sending mail is run.

Note: depending on the operating system and Plesk version, paths can slightly differ. For example: for Debian and Ubuntu use /usr/sbin/sendmail instead of /usr/sbin/sendmail.postfix in the commands below.

RHEL/CentOS

Connect to the server via SSH.
Create a /usr/sbin/sendmail.postfix-wrapper script with the following content:

#!/bin/sh
(echo X-Additional-Header: $PWD ;cat) | tee -a /var/tmp/mail.send|/usr/sbin/sendmail.postfix-bin "$@"
Create /var/tmp/mail.send log file and set a+rw permissions. Make the wrapper executable, rename the old sendmail.postfix file, and link it to the new wrapper:

# touch /var/tmp/mail.send
# chmod a+rw /var/tmp/mail.send
# chmod a+x /usr/sbin/sendmail.postfix-wrapper
# mv /usr/sbin/sendmail.postfix /usr/sbin/sendmail.postfix-bin
# ln -s /usr/sbin/sendmail.postfix-wrapper /usr/sbin/sendmail.postfix
Wait for a while to collect data: 30 -60 min.
Rename sendmail.postfix-bin back to /usr/sbin/sendmail.postfix:

# mv /usr/sbin/sendmail.postfix /root/backup__sendmail.postfix
# mv /usr/sbin/sendmail.postfix-bin /usr/sbin/sendmail.postfix

Note: File /var/tmp/mail.send is not rotated automatically and it is not recommended to leave it for a long period of time as it could consume a server disk space. Delete and create a new file /var/tmp/mail.send after every check up.
Check /var/tmp/mail.send file. There should be lines starting with "X-Additional-Header" pointing to the domain folders where the scripts that sent the mail are located.

The directories, from which mail PHP scripts are run, can be seen using the following command:

# grep X-Additional /var/tmp/mail.send | grep `cat /etc/psa/psa.conf | grep HTTPD_VHOSTS_D | sed -e 's/HTTPD_VHOSTS_D//' `

Note: If no output is shown from the command above, it means no mail was sent using the PHP mail function from the Plesk virtual host's directory.

Usually, that means one of the mail accounts has been compromised. Check the login attempt count:

# zgrep -c 'sasl_method=LOGIN' /var/log/maillog*
/var/log/maillog:221000
/var/log/maillog.processed:362327
/var/log/maillog.processed.1.gz:308956

If an unusually high number of login attempts is shown, it is very likely accounts were compromised. Try identifying these accounts in the following way:

# zgrep -h 'sasl_method' /var/log/maillog* | cut -d' ' -f9 | cut -d= -f2 | sort | uniq -c | sort -nr
891574 [email protected]
To stop spam from being sent, change passwords for the compromised accounts and restart the Postfix service.

Also, check Administrator's Guide