This is a fully transparent proxy-server for POP3-Clients. It runs on a Linux box with iptables (for port re-direction). It can be used to provide POP3 email scanning from the internet, to any internal network and is ideal for helping to protect your "Other OS" LAN from harm, especially when used synergically with a firewall and other Internet Proxy servers.

It is designed to enable scanning of incoming email messages for Viruses, Worms, Trojans, Spam (read as "Un-solicited Bulk Email"), and harmfull attachments. Because viewing HTML mail can enable a "Spammer" to validate an email address (via web bugs), it can also provide dangerous HTML tag stripping.

It works typically in situations where the linux box lies between the network you wish to protect and the "outer world". You have to set up a port redirection rule with iptables (see "IP-Tables / Port redirecting") so that all connections from e.g. inside your office to any POP3 server outside in the world will not leave your router, but come to a local port, on which P3Scan listens. P3Scan receives the original destination address of the "outer world" POP3 server from the Linux kernel and connects to that address.

Anything received from the client will be sent to the server, and vice versa but with a little enhancement: when a message is sent from the server it's parsed, stored into a file, and scanned. If a virus is found a virus notification is sent instead of the original infected message, which can be quarantined or optionally deleted. The message can also be scanned for spam, have potentially dangerous attachments renamed, and have potentially malicious HTML parts stripped.

It should be possible to use any virus scanner using the scannertype=basic configuration option.

Also, P3Scan provides scannertype=avpd for high-speed scanning using for other scan-daemons (trophie, sophie, antivir, ...).

Neither the client nor the server has to be configured. None of them will ever notice that there's a mail scanner. From the server point of view the incoming connections are from the linux box IP. From the client point of wiew the only evidence of the presence of p3scan are virus notifications and some additional X-headers.

iptables - Normally installed by default on major Linux Distributions.
  http://www.netfilter.org
libpcre - Normally installed by default on major Linux Distributions.
  http://www.pcre.org
An Anti-Virus program
  P3Scan is known to work with:
    Kaspersky Anti-Virus for Linux (AVPD)
      http://www.kaspersky.com/
    Trophie Anti-Virus Daemon
      http://www.vanja.com/tools/trophie/
    FRISK F-Prot Antivirus
      http://www.f-prot.com/
    Clam Anti-Virus
      http://www.clamav.net
    Any other virus scanner that can output it's report to the console
    (stdout) so that it can be captured with "2>&1".
DSPAM 3.x (optional) - http://www.nuclearelephant.com/projects/dspam/
Mail::SpamAssassin (optional) - http://www.spamassassin.org
renattach (optional) - http://www.pc-tools.net/unix/renattach/
p3pmail (optional) - http://p3scan.sourceforge.net/#p3pmail

Kernel:

The following kernel-parameters have to be enabled to get P3Scan to work. If you have no clue about kernel-compiling, then here is some good news: Most of Linux Distributions (with kernel 2.4.x or greater) support what we need by default. However, if your distribution does not have it, please read your system documentation on how to add it to your kernel.

   -CONFIG_NETFILTER=y
   -CONFIG_IP_NF_IPTABLES=[y/m]
   -CONFIG_IP_NF_TARGET_REDIRECT=[y/m]

Change to the directory where you untar'ed the program and make any system specific changes as need to the "user options" area of the Makefile, then, as user: $ make and as root (su root) # make install

The only binary will be copied to /usr/sbin/p3scan.

Make install will also copy p3scan.conf and the p3scan-xx.mail files into /etc/p3scan while creating directories /etc/p3scan, /var/run/p3scan, /var/spool/p3scan, /var/spool/p3scan/children, and /var/spool/p3scan/notify. It will also create a symbolic link of /etc/p3scan/p3scan.mail to the language file specified in the Makefile.

After this, you must prepare your configuration file as described below.

Preparing / Manual Configuration:

If you decide not to use "make install" (for example, you don't want gcc on your firewall machine where p3scan is going to run). Please ensure the following directories are created and that they are owned and readable/writable by only the user "mail" (default).

As root, create the following directories: # mkdir /etc/p3scan # mkdir /var/run/p3scan # mkdir -p /var/spool/p3scan/children # mkdir -p /var/spool/p3scan/notify

Make them "owned" by the user "mail" (default): # chown mail.mail /etc/p3scan # chown mail.mail /var/run/p3scan # chown -R mail.mail /var/spool/p3scan

Then make them read/write by only our user: # chmod 700 /etc/p3scan # chmod 700 /var/run/p3scan # chmod -R 700 /var/spool/p3scan

If you don't have the user "mail" and do not know how to create this user, please see your operating systems documentation on how to create a user.

Change the symlink /etc/p3scan/p3scan.mail if you wish (this points to the template which is sent instead of a virus). If you use any special character (like German-umlauts äöü) don't forget to set the charset to "utf8" (charset="utf8" vice charset="iso-8859-1"). Also, ensure the leading dot at the end of the file is there and has a carriage return after the dot.

The configuration file defaults to /etc/p3scan/p3scan.conf

This file is a mixture of configuration data and documentation and MUST be modified to work correctly upon initial installation. You must specify AT LEAST how to call your anti-virus program and how to extract the virus name (if one is found).

The purpose of p3scan is to provide virus protection to an internal network. So, not having a virus scanner is not an option. That being said, if you still do not want a virus scanner enabled, you can just set the scannertype/scanner to basic/"/usr/bin/cat".

Currently, the default configuration is as follows (see p3scan.conf for more info):

   The PID file is stored in: pidfile = /var/run/p3scan/p3scan.pid
   The maximum simultaneous scans is: maxchilds = 10
   We listen to any address: ip = 0.0.0.0
   We listen only on: port = 8110
   targetip and targetport are disabled.
   We run as: user = mail
   We create notification mails in: notifydir = /var/spool/p3scan/notify
      before sending.
   We default to storing infected messages in: virusdir = /var/spool/p3scan
   We keep infected mail.
      "justdelete" is not set.
   We do not check remaining disk space before scanning mail.
      "bytesfree" is not set
   We DO NOT have an Anti-Virus program selected, scanner return code, nor
      regular expression on how to extract a virus name.
      scannertype=basic
      "scanner" is not set
      "viruscode" is not set
      "virusregexp" is not set
   We DO NOT have any "Good" return codes set other than "0" (zero).
      "goodcode" is not set
   We DO NOT demime the message or separate attachments from the original mail
      before scanning.
      "demime" is not set
   We DO NOT send entire lines of email header while processing to keep the
      email client "alive". We send characters instead.
      "broken" is not set.
   We DO NOT check for email marked as "Spam" by your ISP.
      "ispspam" is not set.
   We DO NOT check for "Spam".
      "checkspam/spamcheck" is not set
   We DO NOT rename attachments.
      "renattach" is not pointing to any external program.
   We DO NOT parse HTML code.
      "overwrite" is not set.
   We DO NOT have debug messages being displayed.
      *"debug" is not set.
      * Note: The recommended debug procedure is to call p3scan as such:
         p3scan -d > debug 2>&1
         You can then keep track of the debug messages on another terminal
        with: tail -n 50 -f debug
   We report all program steps to syslog less debug info.
      "quiet" is not set.
   The Virus Report template defaults to /etc/p3scan/p3scan.mail which is
      a symlink to /etc/p3scan/p3scan-xx.mail generated during "make install",
      where xx equals the LANG option set in the Makefile.
   We generate the Virus Report Subject line as:
     "[Virus] found in a mail to you:" <virus name>
     you can change this with the "subject" line in p3scan.conf.
   We generate the Virus Report file disposition line (when justdelete is set):
   notify = Per instruction, the message has been deleted.

   A rule like:

   iptables -t nat -A PREROUTING -p tcp -i eth0 --dport pop3 -j REDIRECT --to 8110
   is enough. Change eth0 to your device for the inbound connections (your
   office or home network).

Also, "pop3" must be defined in your "services" file. Normally /etc/services If it is not defined, enter the definition you have for 110/tcp. IE: pop-3

This rule redirects pop3 connections to a local port (like a pop3 server).

Spam Checking

   The spam checking capability of p3scan has only been tested using
   DSPAM >= 3.0.0-rc2 and Mail::SpamAssassin v2.6-v3.0.1

If using dspam, you need to install the program according to the documentation found at http://www.nuclearelephant.com/projects/dspam/

The recommended procedure is the virtual-users interface of the mysql driver.

If you will be scanning for spam using SpamAssassin, you need to install the program according to the documentation found at http://www.spamassassin.org

The easiest (as fastest) interface to Mail::SpamAssassin is through it's daemon program "spamd" using "spamc".

You can start spamd as follows before running p3scan: *Note: This example is for using SpamAssassin w/mysql /usr/bin/spamd -d -u spamd -x -q &

renattach:

   Is used to rename attachments and is totally configurable.

Renattach must be compiled, installed, and configured before enabling this feature. See the renattach documentation INSTALL and README for further information.

HTML Parsing:

   The HTML parsing option is now an external program to p3scan. This
   facilitates using any program you can find. I have written a separate
   program for this function called p3pmail which can be found on the p3scan
   web site.

P3PMail will obfuscate the tags "href" and "src" the two most dangerous HTML tags (IMHO) for email. Of course, if your using a non-html email client, you will not have to worry about "web-bugs".

Startup:

   Call p3scan without any parameters, it will move into the background.
   You can monitor it's operation via your systems log file.
   You should also test your installation by sending yourself an eicar test
   virus (which will not damage your system). You can get versions of this
   file at http://www.eicar.org/anti_virus_test_file.htm

If you think too much information is being sent to your system logs, you can enable the "quiet" option. This will inhibit "normal" messages.

If P3Scan is started by root, it will change it's user to "mail" (default) after it finishes it's initial startup.

If you are using Mail::SpamAssassin, start spamd BEFORE running p3scan.

RC System / Boot up:

   p3scan comes with two startup scripts, one for FC/RH type systems (init.d),
   and one for Slackware type systems (rc.x). These files will be installed
   depending on your system type. Or, you can add p3scan to your normal default
   startup file. For example, in Slackware place p3scan as follows:

# echo "/usr/sbin/p3scan" >> /etc/rc.d/rc.local

p3scan /etc/p3scan/p3scan.conf /etc/p3scan/p3scan.mail dspam spamd spamc renattach

Please report any bugs to the p3scan support mailing list accessable through:
http://sourceforge.net/projects/p3scan

Jack S. Lai <laitcg at cox dot net>
and contributers (see CONTRIBUTERS file).