p3scan_readme - readme for the p3scan tool
This is a fully transparent proxy-server for POP3, SMTP, and limited
POP3S Clients. It runs on a Linux box with iptables (for port re-
It can be used to provide email scanning from/to the internet, to/from
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 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, POP3S, and SMTP server outside in the world
will not leave your router, but come to a local port, on which P3Scan
P3Scan receives the original destination address of the "outer world"
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. If the message
is destined for a server and a virus is found, the client will be
notified that the server rejected their message due to a virus.
The message can also be scanned for spam, have potentially dangerous
attachments renamed, and have potentially malicious HTML parts
stripped. In the case of incoming messages, this is performed in the
Attachments are scanned/renamed/deleted (optional)
The message is scanned for virus’s
The message is scanned for SPAM (optional)
The message is parsed for web bugs (optional)
It should be possible to use any virus scanner using the
scannertype=basic configuration option. Known to work with this scanner
are FRISK F-Prot and Clam Anti Virus scanners.
P3Scan provides other scannertype’s for scanning using Kaspersky,
Trophie, Clam (TCP) Anti-Virus Daemon’s and also a bash script. Any C
programmer can easily adapt p3scan for other scan-daemons.
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 view 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.
libpcre - Normally installed by default on major Linux Distributions.
ripmime - Needed if your virus scanner does not support email.
An Anti-Virus program
P3Scan is known to work with:
Kaspersky Anti-Virus for Linux (AVPD)
Trophie Anti-Virus Daemon
FRISK F-Prot Antivirus
Any other virus scanner that can output it’s report to the console (stdout) so that it can be captured with "2>&1".
DSPAM (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.
Change to the directory where you untar’ed the program and make any
system specific changes as needed 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
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
Make them "owned" by the user "mail" (default): # chown mail.mail
/etc/p3scan # chown mail.mail /var/run/p3scan # chown -R mail.mail
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
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) 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
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 extract destination url:port from iptables redirected packets.
We run as: user = mail
We create notification mails in: notifydir = /var/spool/p3scan/notify
We default to storing infected messages in: virusdir = /var/spool/p3scan
We keep infected mail.
"justdelete" is not set.
We send emergency notification emails to root and postmaster @localhost.
We notify only the email client when a virus is detected.
"extra" is not set.
We use the default /bin/mail to send extra notification email when required.
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.
"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
"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.
The default timeout is 30 seconds when processing a large email message.
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 pointing to any external program.
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 do not copy the virus template message for the bash scanner to modify.
"altvnmsg" is not set.
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.
When an outgoing message is rejected, the default of "Virus detected! P3scan
rejected message!" is used.
Outgoing message size is not checked before parsing.
The port for SSL messages is 995.
We do not generate Virus Definition data for outgoing/notification messages.
"footer" is not set.
IP-Tables / Port redirecting:
iptables -t nat -A PREROUTING -p tcp -i eth0 --dport pop3 -j REDIRECT --to 8110
iptables -t nat -A PREROUTING -p tcp -i eth0 --dport smtp -j REDIRECT --to 8110
iptables -t nat -A PREROUTING -p tcp -i eth0 --dport pop3s -j REDIRECT --to 8110
are enough. Change eth0 to your device for the inbound connections (your
office or home network).
Also, "pop3", "smtp", and/or "pop3s" must be defined in your "services" file.
Normally locate at: /etc/services.
If it is not defined, enter the definition you have for 110/tcp. IE: pop-3, or
just enter the port number(s). IE: 110, 25, or 995
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
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 &
SSL Message parsing:
We are able to perform limited checking of messages using SSL.
To use this feature, you must tell your email client NOT to use SSL and just
change the pop3 port from 110 to 995. If p3scan sees a destination port of 995
(or whatever port "sslport" is set to) it will initiate an SSL conversation.
NOTE: This is limited support as p3scan will not show you the SSL certificate
and will just accept any certificate as sent by the actual server.
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-
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
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
RC System / Boot up: "make install" should determine the correct p3scan
startup file and place it in the proper directory.
If for some reason this does not happen, 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
and please notify the p3scan-main mailing list of this problem.
BUGS/SUPPORT 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