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.\"
.\" Copyright (c) 2004, Stefan Walter
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\"
.\" * Redistributions of source code must retain the above
.\" copyright notice, this list of conditions and the
.\" following disclaimer.
.\" * Redistributions in binary form must reproduce the
.\" above copyright notice, this list of conditions and
.\" the following disclaimer in the documentation and/or
.\" other materials provided with the distribution.
.\" * The names of contributors to this software may not be
.\" used to endorse or promote products derived from this
.\" software without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
.\" "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
.\" LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
.\" FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
.\" COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
.\" BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
.\" OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
.\" AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
.\" THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
.\" DAMAGE.
.\"
.\"
.\" CONTRIBUTORS
.\" Stef Walter <stef@memberwebs.com>
.\"
.Dd September, 2004
.Dt clamsmtpd 8
.Os clamsmtp
.Sh NAME
.Nm clamsmtpd
.Nd an SMTP server for scanning viruses via clamd
.Sh SYNOPSIS
.Nm
.Op Fl d Ar level
.Op Fl f Ar configfile
.Op Fl p Ar pidfile
.Nm
.Fl v
.Sh DESCRIPTION
.Nm
is an SMTP filter that allows you to check for viruses using the ClamAV
anti-virus software. It accepts SMTP connections and forwards the SMTP commands
and responses to another SMTP server.
.Pp
The DATA email body is intercepted and scanned before forwarding. By default email
with viruses are dropped silently and logged without any additional action taken.
.Pp
.Nm
aims to be lightweight and simple rather than have a myriad of options. The options
it does have are configured by editing the
.Xr clamsmtpd.conf 5
file. See the man page for
.Xr clamsmtpd.conf 5
for more info on the default location of the configuration file.
.Sh OPTIONS
Previous versions had more options. These still work for now but have equivalents in
.Xr clamsmtpd.conf 5
and are not documented here. The options are as follows.
.Bl -tag -width Fl
.It Fl d
Don't detach from the console and run as a daemon. In addition the
.Ar level
argument specifies what level of error messages to display. 0 being
the least, 4 the most.
.It Fl f
.Ar configfile
specifies an alternate location for the
.Nm
configuration file. See
.Xr clamsmtpd.conf 5
for more details on where the configuration file is located by default.
.It Fl p
.Ar pidfile
specifies a location for the a process id file to be written to. This file
contains the process id of
.Nm
and can be used to stop the daemon.
.It Fl v
Prints the clamsmtp version number and exits.
.El
.Sh LOGGING
.Nm
logs to
.Xr syslogd
by default under the 'mail' facility. You can also output logs to the console
using the
.Fl d
option.
.Sh LOOPBACK FEATURE
In some cases it's advantageous to consolidate the virus scanning and filtering
for several mail servers on one machine.
.Nm
allows this by providing a loopback feature to connect back to the IP that an
SMTP connection comes in from.
.Pp
To use this feature specify only a port number (no IP address) for the
.Ar OutAddress
setting in the configuration file. This will cause
.Nm
to pass the email back to the said port on the incoming IP address.
.Pp
Make sure the
.Ar MaxConnections
setting is set high enough to handle the mail from all the servers without refusing
connections.
.Sh TRANSPARENT PROXY FEATURE
A transparent proxy is a configuration on a gateway that routes certain types of
traffic through a proxy server without any changes on the client computers.
.Nm
has support for transparent proxying of SMTP traffic by enabling the
.Ar TransparentProxy
setting. This type of setup usually involves firewall rules which redirect traffic to
.Nm
and the setup varies from OS to OS. The SMTP traffic will be forwarded to it's
original destination after being scanned.
.Pp
When doing transparent proxying for outgoing email it's probably a good idea to
turn on bounce notifications using the
.Ar Action: bounce
setting. Also note that some features (such as SSL/TLS) will not be available
when going through the transparent proxy.
.Pp
Make sure that the
.Ar MaxConnections
setting is set high enough for your transparent proxying. Because
.Nm
is not being used as a filter inside a queue, which usually throttles the amount
of email going through, this setting may need to be higher than usual.
.Sh VIRUS ACTIONS
Using the
.Ar VirusAction
option you can run a script or program whenever a virus is found. This may
be handy in certain circumstances but it has several drawbacks. For one, the
performance of the virus filtering will take a hit, perhaps DOS'ing your
machine under heavy load. Secondly as with running any program there are
security implications to be considered.
.Pp
.Please consider the above carefully before implementing a virus action.
.Pp
The script is run without its output being logged, or return value being
checked. Because of this you should test it thoroughly. Make sure it runs
without problems under the user that
.Xr clamsmtpd 8
is being run as.
.Pp
Various environment variables will be present when your script is run. You
may need to escape them properly before use in your favorite scripting
language. Failure to do this could lead to a REMOTE COMPROMISE of your
machine.
.Bl -tag -width Fl
.It Ar CLIENT
The network address of the SMTP client connected.
.It Ar EMAIL
When the
.Ar Quarantine
option is enabled, this specifies the file that the virus was saved to.
.It Ar RECIPIENTS
The email addresses of the email recipients. These are specified one per
line, in standard address format.
.It Ar REMOTE
If
.Nm
is being used to filter email between SMTP servers, then this is the
IP address of the original client. In order for this information to be present
(a) the SMTP client (sending server) must an send an XFORWARD command and (b)
the SMTP server (receiving server) must accept that XFORWARD command without
error.
.It Ar REMOTE_HELO
If
.Nm
is being used to filter email between SMTP servers, then this is the
HELO/EHLO banner of the original client. In order for this information to be present
(a) the SMTP client (sending server) must an send an XFORWARD command and (b)
the SMTP server (receiving server) must accept that XFORWARD command without
error.
.It Ar SENDER
The email address for the sender of the email.
.It Ar SERVER
The network address of the SMTP server we're connected to.
.It Ar TMPDIR
The path to the temp directory in use. This is the same as the
.Ar TempDirectory
option.
.It Ar VIRUS
The name of the virus found.
.El
.Sh SECURITY
There's no reason to run this daemon as root. It is meant as a filter and should
listen on a high TCP port. It's probably a good idea to run it using the same
user as the
.Xr clamd 8
daemon. This way the temporary files it writes are accessible to
.Xr clamd 8
.Pp
Care should be taken with the directory that
.Nm
writes its temporary files to. In order to be secure, it should not be a world
writeable location. Specify the directory using the
.Ar TempDirectory
setting.
.Pp
When using the
.Ar VirusAction
option make sure you understand the security issues involved. Unescaped
environment variables can lead to execution of arbitrary shell commands
on your machine.
.Pp
If running
.Nm
on a publicly accessible IP address or without a firewall please be sure to
understand all the possible security issues. This is especially true if the
loopback feature is used (see above).
.Sh SEE ALSO
.Xr clamsmtpd.conf 5
.Xr clamd 8 ,
.Xr clamdscan 1
.Sh AUTHOR
.An Stef Walter Aq stef@memberwebs.com
|
