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Friday, November 11. 2011

Exim TLS Configuration On FreeBSD

Configured Exim to work with Transport Layer Security (TLS) a few days ago. Really I should have done this at the time I set up Exim, SASLauthd, ClamAV and SpamAssassin but hey ho. Instead I've endured years of bots trying to brute force passwords via SMTP (for which I ended up using various means to block them by detecting hits in the logfiles, another entry completely!).

Anyway yes finally got around to it so this is how I did it (this should work out of the box on a fresh installation of Exim on FreeBSD):

Create A Self Certified SSL Certificate
First of all I created a self signed ssl certificate using this command:

CODE:

openssl req -x509 -newkey rsa:1024 -keyout /etc/mail/exim.crt -out /etc/mail/exim.crt -days 9999 -nodes

After issuing that command you're prompted for a few details like company details, organizational role, etc etc, no big deal. Really if you're running a 'proper' email server (ie one used by a lot of people) then you need to get your certificate signed properly by a Certificate Authority (CA) - using a self certified certificate you will be prompted when you go to login to the server with a warning about how the certificate is not valid - but since there's only me using the server nowadays it doesn't really matter and I can just add an exception into my email client to allow the certificate even though it's not valid.

Modify Exim Configuration
Next go on to modify the exim config so it uses TLS. With each of the following items of config you probably want to check to see if they're already in teh default config but commented out, I know most of it is in there:

CODE:

tls_advertise_hosts = *
tls_certificate = /etc/mail/exim.crt
tls_privatekey = /etc/mail/exim.crt
auth_advertise_hosts = ${if eq{$tls_cipher}{}{}{*}}

I think the last setting 'auth_advertise_hosts' is probably not in by default - that option basically says 'only advertise authentication if a connection is using TLS'. I must admit I don't fully understand the mechanics of it all but as I understand it, it's this that is key to cutting down on brute force attacks, because brute force attackers generally just blindly use the basic AUTH commands via SMTP and don't ever bother trying to use TLS.

With that added to the configuration file it's just left to restart the exim server and you should be good to go.

Notes
When you login via telnet now to test it out you should see that AUTH isn't available unless you've already started a TLS session (which you have to do with the STARTTLS command). You won't be able to test the authentication out after issuing STARTTLS via telnet because the conversation has to be encrypted after that point. I think I read somewhere you can use openssl to test it out though I didn't try.

Another thing to watch out for, briefly mentioned above, is that you must set up your email client to allow the invalid/self certified certificate that the server uses. If you don't do that then you won't be able to send email using authentication via the server. The first time you try and send an email using auth via the server from your email client, it should pop up a dialog box that allows you to allow the cert even though it's invalid.

Posted by munk in Email, Security at 19:32 | Comments (0) | Trackbacks (0)

Wednesday, August 15. 2007

Command Line Web Browsing With WWW::Mechanize::Shell

Introduction
The perl module WWW::Mechanize::Shell is a brilliant tool for browsing websites at a very low level - think somewhere in between using telnet and using a command line based browser like lynx or links or w3m and you'll be close. WWW::Mechanize::Shell is more than that though, it allows you to script a complete HTTP session so it can be replayed back at a later date without any interaction using WWW::Mechanize::Shell's parent perl module WWW::Mechanize - great for automatically submitting HTML forms/ POST data regularly via a cron job for example.

In this article I'll be talking about installing WWW::Mechanize::Shell, look at a typical WWW::Mechanize::Shell browsing session and look at some examples of how I use WWW::Mechanize::Shell to make things easier. Finally the article will end with a real world example - using mechshell to automate logging into FreshPorts and updating a watch list.

Installing WWW::Mechanize::Shell
As the name suggests, WWW::Mechanize::Shell is a perl module whose 'parent' is the WWW::Mechanize module written by Andy Lester (WWW::Mechanize::Shell itself is written by Max Maischein at time of original writing). WWW::Mechanize does all the work in the background - WWW::Mechanize::Shell just makes it easy to interact in a HTTP session. WWW::Mechanize::Shell and all it's dependencies can be installed from the ports tree:

CODE:

root@users /root# cd /usr/ports/www/p5-WWW-Mechanize-Shell/
root@users /home/munk/ports/www/p5-WWW-Mechanize-Shell# make install
root@users /home/munk/ports/www/p5-WWW-Mechanize-Shell# rehash

Getting Started Using WWW::Mechanize::Shell
Once installed, start up the WWW::Mechanize::Shell using the following you can use the following commandline:

CODE:

root@users /root# perl -MWWW::Mechanize::Shell -eshell

To make things easier though I use a CSH shell alias which aliases 'mechshell' to the command above:

CODE:

root@users /root# grep mechshell $cshrc
alias mechshell perl -MWWW::Mechanize::Shell -eshell

Examples of WWW::Mechanize Usage
I usually use WWW::Mechanize when I want to manipulate data from websites that require a stateful HTTP session - ie a browsing session where there's more than one URL you have to visit to complete the 'session'. Usually these kind of stateful sessions involve logging into the website first, then browsing to another page to obtain the data and then I have the WWW::Mechanize perl script handle the data and return any results on the commandline.

Some examples of scripts that I've use WWW::Mechanize with:

eclipse_flex_speed.pl
My ISP (Eclipse UK) used to allow you to 'flex' your internet speed from 256k up to 2Mbps. They ran an offer for a while where you could flex to the max for 3 months - unfortunately you could only flex for 12 hours at a time, which meant logging into the control panel every 12hrs, selecting the maximum speed and then submitting the form. PITA basically.

Instead I wrote eclipse_flex_speed.pl to automatically login to the Eclipse control panel, 'click' the 2Mbps radio button and then submit the form so my speed got flexed automagically. I then added the script as a cron job to autorun every 12hours, saving the haslle of doing it all manually!

aod_get.pl
The BBC website allows you to listen to streams of all BBC radio broadcasts for up to a week after they've been aired live. The problem is that the web interface you listen to the stream on in your web browser only allows you to skip 5 or 15 minutes ahead in time and doesn't allow you to go to specific times in the stream. To get around this you can obtain the URL of the real player stream and open it in a standalone real player - doing this you can go to any point in the stream easily. Trouble is finding the URL of the stream isn't that easy and involves viewing the source HTML of the web UI and copy/pasting a partial URL.

I started to write a WWW::Mechanize script to automate the 'screen scraping' of all the available feeds from the BBC Audio On Demand site and listing them on one single HTML page linking the name of the feed to the real player feed URL. As it goes though, someone else - Dave Cross - already had the same idea and wrote a great script for scraping the BBC feeds automatically. I now run this in a cronjob once a week.

torrentflux_ctl.pl
This is a script for starting and stopping all torrents under the control of the torrentflux web based bittorrent client. The script logs in as the torrent owner and then stops or starts all the torrents for that user - basically just does a GET of a URL that causes torrentflux to stop or start all torrents. Crude but effective.

Real world example - Automating the update of FreshPorts watch list
Below is a real world example usage of WWW::Mechanize::Shell - automating the procedure of updating your watch list on Freshports.org. I've included comments as '# this is a comment' to help explain what each command is doing.

CODE:

# Start up mechshell - alias for 'perl -MWWW::Mechanize::Shell -eshell':
munk@users /home/munk# mechshell

# Request the URL http://www.freshports.org/login.php.
# Note the HTTP response '(200)' is displayed underneath
# to indicate the page was fetched successfully:
(no url)>get http://www.freshports.org/login.php
Retrieving http://www.freshports.org/login.php(200)

# Use the mechshell 'dump' command to dump the contents
# of all forms found on the login page:
http://www.freshports.org/login.php>dump
POST http://www.freshports.org/login.php?origin=%2F [l]
 custom_settings=1 (hidden readonly)
 LOGIN=1 (hidden readonly)
 UserID= (text)
 Password= (password)
 submit=Login (submit)
 <NONAME>=<UNDEF> (reset)

# There's just a single form on this page:
# - the form's 'ACTION' is set to submit the form using the POST method
# to the url http://www.freshports.org/login.php?origin=%2F
# The form contains the following form fields:
# - 2 hidden fields
# - 1 text field called 'UserID'
# - 1 password field called 'Password'
# - 1 submit field called 'Login'

# Fill in the 'UserID' and 'Password' fields:
http://www.freshports.org/login.php>value UserID munk
http://www.freshports.org/login.php>value Password xxxxxx

# And then submit the form. Note we can just use the mechshell 'submit'
# command here because there is only a single form on the page. If there were
# more than one form on the page we would need to specify which button exactly to
# click:
http://www.freshports.org/login.php>submit
200

# Again note that the '200' response indicates the request was successful.
# Also note that the next mechshell prompt below has changed from
# 'http://www.freshports.org/login.php>' to just 'http://www.freshports.org/' -
# this indicates that the login script has probably redirected us to the
# freshports home page.

# Now we take a look to check that the login succeeded ok. To do this we use
# the mechshell 'content' command which effectively dumps the content of the
# returned page back at us in a pager.
# What we're looking for is the text 'Logged in as munk' which will indicate we
# logged in ok:
http://www.freshports.org/>content
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<HTML>
<HEAD>
-snip-
 <td NOWRAP>Logged in as munk <a href="/customize.php?origin=%2F" title="Customize your settings">Customize</a
> <a href="/logout.php" title="Logout of the website">Logout</a> <a href="/my-flagged-commits.php" title="Li
st of commits you have flagged">My Flagged Commits</a> 
-snip-

# Now we're logged in ok we can continue to upload the mypkg_info.txt file we
# created earlier.

# First browse to the pkg_upload.php page:
http://www.freshports.org/>get http://www.freshports.org/pkg_upload.php
Retrieving http://www.freshports.org/pkg_upload.php(200)

# Now use 'dump' to see a list of form fields on this page.
# Note that there are 2 submit buttons on this page:
http://www.freshports.org/pkg_upload.php>dump
POST http://www.freshports.org/pkg_upload.php (multipart/form-data)
 pkg_info= (file)
 staging=Staging (submit)
 wlid=5393 (option) [*5393/main*]
 replaceappend=replace (radio) [*replace/Replace list contents|append/Append to list (duplicates will be removed)]
 upload=Upload (submit)

# We need to fill out the form here. Uploading files with mechshell is as
# simple as completing the correct file type field:
http://www.freshports.org/pkg_upload.php>value pkg_info /tmp/mypkg_info.txt

# Ok, now we're ready to submit the form.
# Note that because there are 2 submit buttons on this form, we must explicitly
# tell mechshell which button it is that we want to click on - to do that we use
# the 'click' command. Just using 'submit' here would possibly click on the
# 'staging' button which is not what we want - instead we use the command
# 'click upload' to indicate we want to click on the 'upload' button:
http://www.freshports.org/pkg_upload.php>click upload
(200)

# Success! It's a good idea now to just check that this worked by browsing in
# a web browser to your watch list and checking the new items were updated ok (of
# course you can do this in mechshell if you want but I'll leave that out here!).

# Finally, the really cool bit. The mechshell 'script' command will dump out
# the perl code required to perform all of the above actions again if you copy
# them into a perl script:
http://www.freshports.org/pkg_upload.php>script
#!perl -w
use strict;
use WWW::Mechanize;
use WWW::Mechanize::FormFiller;
use URI::URL;
-snip-

# Also, if you provide a filename as an argument to the 'script' command,
# mechshell will dump all the script commands to that filename:
http://www.freshports.org/pkg_upload.php>script /tmp/freshports_update.pl

# Finally, use 'quit' to exit the mechshell:
http://www.freshports.org/pkg_upload.php>quit
munk@users /home/munk#

Now all that remains is to open up /tmp/freshports_update.pl and tidy the script up so that it's more suitable for automated use via cron. For example, any 'dump' and 'content' commands can be taken out - these would only cause problems anyway if run from a non-interactive shell as used by cron.

We also need to add some code to have the script dump the contents of 'pkg_info -qoa' to a temporary file prior to uploading.

The completed 'quick and dirty' hack looks like this then:

CODE:

#!/usr/bin/perl -w
use strict;
use WWW::Mechanize;
use WWW::Mechanize::FormFiller;
use URI::URL;

# FreshPorts username/pass:
my $user="munk";
my $pass="xxxxx";

# Temp location to store output from 'pkg_info -qoa':
my $mypkg_info="/tmp/freshports/mypkg_info.txt";

# prepare file containing output from: pkg_info -qoa
`pkg_info -qoa > $mypkg_info`;

# Prepare WWW::Mechanize:
my $agent = WWW::Mechanize->new( autocheck => 1 );
my $formfiller = WWW::Mechanize::FormFiller->new();
$agent->env_proxy();

# Login to FreshPorts:
$agent->get('http://www.freshports.org/login.php');
$agent->form_number(1) if $agent->forms and scalar @{$agent->forms};
{ local $^W; $agent->current_form->value('UserID', $user); };
{ local $^W; $agent->current_form->value('Password', $pass); };
$agent->submit();

# Submit pkg_info details to FreshPorts pkg_upload page:
$agent->get('http://www.freshports.org/pkg_upload.php');
$agent->form_number(1) if $agent->forms and scalar @{$agent->forms};
{ local $^W; $agent->current_form->value('pkg_info', $mypkg_info); };
$agent->click('upload');

# Remove temporary file:
`rm $mypkg_info`;

After saving the script and making the file executable, an entry can then be added to cron to have the script auto update the list of ports at freshports once a week - or however often you require it to be updated, once a week is more than enough for me. Sorted! :)

Posted by munk in Perl, Ports, Shell at 13:46 | Comments (3) | Trackbacks (0)

Thursday, February 1. 2007

Migrating server to new hdd

Never know quite how to describe this 'migration' - it's the same old bits in the machine but I've built a new installation of FreeBSD onto a new HDD and am now putting this new 'server' (hdd!) into the old machine! Sounds pretty weak/easy maybe but it's taken me almost a month to get this done what with migrating various bits and bobs and tidying up crap along the way - together with a heavy dose of procrastination along with it all. Just managed to whittle the MySQL dbs down to about 25% of what they used to be, so many dbs and users that haven't used anything since 2003 or so!

Mind, not that it's active that much now, we're talking maybe a dozen users or so...

Anyway, still got a lot to do, the server is just about running now with the new HDD, managed to get named up and running along with apache, exim and mysql with all the data more or less migrated over now. There *will* be lots of problems with web services but that can wait for now, nothing that can't wait til tomorrow.

Posted by munk in General at 00:56 | Comments (0) | Trackbacks (0)

Wednesday, January 17. 2007

Installing Exim, SASLAuthd, ClamAV and SpamAssassin on FreeBSD 6.2

Introduction
This article describes the steps necessary to install and configure Exim on FreeBSD 6.2 with support for the following:

authenticated SMTP (asmtp) using SASLAuthd
spam detection and quarantine using SpamAssassin
malware detection and quarantine using ClamAV

Each of the required 'dependencies' or components will be installed and configured, Exim will be installed and configured and finally we will test to check each component is working as required.

With regards to spam and malware scanning, the system described will quarantine any files/messages that it finds classified as spam or malware. In this way the quarantined files can be checked over by the admin at a later date and various stats gathering can be done if required.

Installing and Configuring SASLAuthd
SASLAuthd is an authentication daemon that can handle authentication requests from 3rd party applications such as Exim - generally for any application that can't directly access a system password database because of permission restrictions. In this case running Exim MTA as 'root' is a potential security risk, so exim runs as the 'mailnull' user on FreeBSD. Unfortunately this means Exim can't easily read the system password database to authenticate users who want to send mail via the server, which is where SASLAuthd comes in. Any requests for authentication with Exim are passed on to the SASLAuthd daemon which will then verify whether the user credentials are valid - if so, the email is delivered, if not, it's rejected.

Install SASLAuthd from the FreeBSD ports tree:

CODE:
root@win /root# cd /usr/ports/security/cyrus-sasl2-saslauthd/
root@win /usr/ports/security/cyrus-sasl2-saslauthd# make install
...
root@win /usr/ports/security/cyrus-sasl2-saslauthd# rehash
Configure SASLAuthd to run at boot.

Edit /etc/rc.conf to include the following:

CODE:
saslauthd_enable="YES"
saslauthd_flags="-a getpwent"

Note:
SASLAuthd will run using the 'getpwent' authentication mechanism with the flag above. This method uses the passwd file directly instead of using other means like kerberos or PAM. If you require another method, check the manpage for saslauthd.
Start the SASLAuthd daemon running:

CODE:
root@win /usr/ports/security/cyrus-sasl2-saslauthd# cd /usr/local/etc/rc.d
root@win /usr/local/etc/rc.d# ./saslauthd start
(Optional) Test the SASLAuthd daemon:

Substitute 'user' and 'pass' for the username and password of a user
account on your system:

CODE:
root@win /usr/local/etc/rc.d# testsaslauthd -u user -p pass
0: OK "Success."

Installing and Configuring SpamAssassin
SpamAssassin (SA) is one solution to the problem of spam. SA can run as a daemon (spamd) in the background and accept requests from an MTA such as Exim to check whether an email message should be classified as spam.

Spamd looks at the message and checks for various factors that make the message more or less likely to be spam and assigns the message a score based on what it finds. Spamd will then reply to the MTA, telling it the spam score that it gave that message. The MTA can then decide - based on that score - whether to accept/reject the message - or in the case of this guide whether to instead quarantine the message.

Install SA from the FreeBSD ports.

Note:
There are various installation options you can choose when installing SA which you should see when you first run 'make install' in the SA port directory. To see the options after already configuring them you can run 'make config'.

In turn, each of SA's dependencies may also have options you can configure at install time.

To write this guide I'm only using the single option 'AS_ROOT' in the SA install configuation and for the other items generally just choose the
defaults.

CODE:
root@win /root# cd /usr/ports/mail/p5-Mail-SpamAssassin/
root@win /usr/ports/mail/p5-Mail-SpamAssassin# make install

Once complete, you should see:

CODE:
*************************************************************************
*           _  _____ _____ _____ _   _ _____ ___ ___  _   _             *
*          / \|_   _|_   _| ____| \ | |_   _|_ _/ _ \| \ | |            *
*         / _ \ | |   | | |  _| |  \| | | |  | | | | |  \| |            *
*        / ___ \| |   | | | |___| |\  | | |  | | |_| | |\  |            *
*       /_/   \_\_|   |_| |_____|_| \_| |_| |___\___/|_| \_|            *
*                                                                       *
*       See /usr/local/share/doc/p5-Mail-SpamAssassin/INSTALL,          *
*       and /usr/local/share/doc/p5-Mail-SpamAssassin/UPGRADE,          *
*       or http://spamassassin.org/dist/INSTALL and                     *
*       http://spamassassin.org/dist/UPGRADE BEFORE enabling            *
*       this version of SpamAssassin for important information          *
*       regarding changes in this version.                              *
*************************************************************************

It's a good idea to read the files listed in the banner above. SA has a large number of options that can be configured; a good place to start configuring options on FreeBSD is in /usr/local/etc/mail/spamassassin/.
Configure SA to run at boot.

Edit /etc/rc.conf to include the following:

CODE:
spamd_enable="YES"
Start SA spamd.

We can now go on to actually start spamd running as a daemon and verify spamd started ok:

CODE:
root@win /root# cd /usr/local/etc/rc.d
root@win /usr/local/etc/rc.d# rehash
root@win /usr/local/etc/rc.d# ./sa
sa-spamd* saslauthd*
root@win /usr/local/etc/rc.d# ./sa-spamd start
Starting spamd.
munk@win /usr/local/etc/rc.d# ./sa-spamd status
spamd is running as pid 754.

This tells us spamd is running ok in the background.

Installing and Configuring ClamAV
ClamAV is an anti-virus suite and includes a daemon clamd (runs in the background to check for requests to test for virii), another daemon freshclam (updates the virus definition database) and a couple of clients to run on the commandline if you need them for local virus scanning.

Exim will send requests to the clamd server in much the same was as spamd does - if clamd classifies a message as containing a virus, Exim will reject delivery of the message and instaed quarantine it.

Install ClamAV from the FreeBSD ports tree:

CODE:
root@win /root# cd /usr/ports/security/clamav
root@win /usr/ports/security/clamav# make install
Configure ClamAV to start at boot time.

Edit /etc/rc.conf to include:

CODE:
clamav_clamd_enable="YES"
clamav_freshclam_enable="YES"
Configure clamd.

Edit /usr/local/etc/clamd.conf to include the following:

CODE:
LogFile /var/log/clamav/clamd.log
PidFile /var/run/clamav/clamd.pid
DatabaseDirectory /var/db/clamav
LocalSocket /var/run/clamav/clamd
FixStaleSocket
User clamav
AllowSupplementaryGroups
ScanMail
ScanArchive
Start clamd and freshclam.

CODE:
root@win /root# cd /usr/local/etc/rc.d
root@win /usr/local/etc/rc.d# ./clamav-clamd start
Starting clamav_clamd.
root@win /usr/local/etc/rc.d# ./clamav-freshclam start
Starting clamav_freshclam.

Note:
You may see the following message on first running clamd:

CODE:
LibClamAV Warning: **************************************************
LibClamAV Warning: *** The virus database is older than 7 days. ***
LibClamAV Warning: *** Please update it IMMEDIATELY! ***
LibClamAV Warning: **************************************************

As long as you're running freshclam, you can safely ignore this message. Freshclam should update your definitions automatically. Be sure to configure freshclam to update the virus definitions regularly.

ClamAV should be configured now and ready to accept request to check for malware from the Exim MTA.

We can now move on finally to install and configure Exim.

Installing and Configuring Exim
Exim configuration can be very complicated. This guide will only deal with the configuration of Exim so it accepts mail on a domain 'mail.example.com', scans the mail for malware/spam - quarantining anything it finds as malware/spam and accepts authentication requests correctly.

Important:
Ensure your mail server's DNS is configured correctly and preferably has a reverse DNS record (rDNS) set up. Many mail servers will not deliver mail correctly to/from your mail server without rDNS.

Install Exim from the FreeBSD ports tree:

CODE:
[12:10:57] root@win /root# cd /usr/ports/mail/exim
[12:12:30] root@win /usr/ports/mail/exim# make -DWITH_CONTENT_SCAN -DWITH_SASLAUTHD install
Stop the Sendmail daemon if it's already running:

CODE:
root@win /root# cd /etc/rc.d
root@win /etc/rc.d# ./sendmail stop
Configure Exim to run at boot time.

Edit /etc/rc.conf to include:

CODE:
sendmail_enable="NO"
sendmail_submit_enable="NO"
sendmail_outbound_enable="NO"
sendmail_msp_queue_enable="NO"
exim_enable="YES"

This has the effect of disabling sendmail at boot time - the default FreeBSD MTA - and running Exim instead.
Configure mailer.conf to use Exim as the default MTA.

Edit /etc/mail/mailer.conf to read:

CODE:
sendmail          /usr/local/sbin/exim
send-mail         /usr/local/sbin/exim
mailq             /usr/local/sbin/exim -bp
newaliases        /usr/bin/true

This will allow any FreeBSD base system mail related commands to use Exim instead of Sendmail.

Configuring Exim
We now move on to configuring Exim.

Set the primary hostname.

Edit /usr/local/etc/exim/configure.

Find and edit the 'primary_hostname' line for your domain:

CODE:
primary_hostname = example.com

This configures Exim to accept mail primarily for the 'example.com' domain - ie foobar@example.com.
Find and edit the following lines to read:

CODE:
av_scanner = clamd:/var/run/clamav/clamd
spamd_address = 127.0.0.1 783
Configure the malware and spam Access Control Lists (ACLs).

How malware/spam checking works in this system:
We add a check in the acl_check_data ACL for spam and malware. Exim will request each email is checked for spam/malware by the relevant daemon - spamd for spam, clamd for malware. If the message is classified as spam/malware by the relevant daemons, Exim will add a header to the message 'X-Quarantine-Me-Spam' (similar for malware).

Later on when it comes to actually delivering (termed 'routing' in Exim terminology), we add two routers to test for the existence of the headers that are added in the acl_check_data ACL if a message is found to be spam/malware. If the headers are found by the malware/spam routers, the message is not delivered but instead copied to a quarantine location on disk.

This quarantine location can then be checked later by an admin to check if anything is amiss - ie regular non spam/malware mail that should really have been delivered.

Once you're satisfied the configuration is working as it should - ie after a few months of operation - and not finding false positives, you can change the malware/spam acl checks to just deny instead of adding the quarantine headers. Having said that, I still opt to just quarantine malware/spam and remove it at a later date.

On to configuring the data ACL:

Modify the acl_check_data ACL to read/include:

CODE:
acl_check_data:

  # Deny if the message contains a virus. Before enabling this check, you
  # must install a virus scanner and set the av_scanner option above.
  #
  # defer_ok - pass this message if scanner is down etc:
  warn  message         = X-Quarantine-Me-Malware: $malware_name
        log_message     = malware: $malware_name
        demime          = *
        malware         = */defer_ok

  # Add headers to a message if it is judged to be spam. Before enabling this,
  # you must install SpamAssassin. You may also need to set the spamd_address
  # option above.
  #
  warn    message       = X-Quarantine-Me-Spam: SA score $spam_score\n\
                          X-SA-Report: $spam_report
          log_message   = Spam score $spam_score > 5
          spam          = spamd/defer_ok
          condition     = ${if >{$spam_score_int}{50}{1}{0}}

  # Accept the message.

  accept

At the top of the routers section, modify to read/include:

CODE:
begin routers

check_malware:
  driver                = redirect
  condition             = ${if def:h_X-Quarantine-Me-Malware: {1}{0}}
  headers_add           = X-Quarantined-Malware: $h_X-Quarantine-Me-Malware:
  headers_remove        = X-Quarantine-Me-Malware
  data                  = /var/quarantine/malware/malware.$tod_logfile
  file_transport        = address_file

check_spam:
  driver                = redirect
  condition             = ${if def:h_X-Quarantine-Me-Spam: {1}{0}}
  headers_add           = X-Quarantined-Spam: $h_X-Quarantine-Me-Spam:
  headers_remove        = X-Quarantine-Me-Spam
  data                  = /var/quarantine/spam/spam.$tod_logfile
  file_transport        = address_file

no_more

Modify the authenticators section to read:

CODE:
begin authenticators
plain:
driver = plaintext
public_name = PLAIN
server_condition = ${if saslauthd{{$2}{$3}}{1}{0}}

login:
driver = plaintext
public_name = LOGIN
server_prompts = "Username:: : Password::"
server_condition = ${if saslauthd{{$1}{$2}}{1}{0}}

Save the /usr/local/etc/exim/configuration file.
Create the quarantine directories and change ownership to mailnull:mail:

CODE:
root@win /root# mkdir -p /var/quarantine/{malware,spam}
root@win /root# chown mailnull:mail /var/quarantine/{malware,spam}
Restart Exim to suck in the new config options:

CODE:
root@win /root# /usr/local/etc/rc.d/exim restart
Stopping exim.
Starting exim.

Exim should now be set to check for malware/spam and to authenticate users.

Testing Exim configuration
Finally we can move on to test that our config works correctly for spam/malware checking and for authenticating users.

Testing Exim's malware/spam scanning.

The easiest option is to send an email to your mailserver with specially crafted malware/spam signatures included in the body of the message. When spamd/clamd see these signature strings in the body of the messages, they should classify the message as spam/malware and Exim in turn will quarantine the messages.

The official EICAR malware/virus testing signature is as follows:

CODE:
X5O%@AP[4\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILEspamcH+H*

See here for the official string:

http://www.eicar.org/anti_virus_test_file.htm

The official GTUBE spam testing signature is as follows:

CODE:
XJS*C4JDBQADN1.NSBN3*2IDNEN*GTUBE-STANDARD-ANTI-UBE-TEST-EMAIL*C.34X

See here for the official string:

http://spamassassin.apache.org/gtube/

Note:
Another option for testing spam/malware scanning is to run exim from the commandline using the command 'exim -bh 127.0.0.1'. This will run an SMTP session from the commandline (think telnet) and allow you to inject your own specially crafted message using the signatures above. This requires you enter a valid SMTP session, something like:

CODE:
HELO example.com
MAIL FROM:foo@example.com
RCPT TO:foo@example.com
DATA
X5O%@AP[4\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILEspamcH+H*
.

This would simulate the injection of a mail message with a virus in it and in 'exim -bh' mode you can see a lot of useful debugging info to verify everything works ok.
Testing Exim's Authentication configuration.

We can now test that ASMTP is working. For this you can either run exim in one of it's many excellent debugging modes or you can simply configure a remote email client to use ASMTP. This guide will use the commandline to test ASMTP.

Important:
Before attempting this method please read the exim documentation on how ASMTP works. The following assumes you have read and understood that text.

First create a simple perl script called 'encode' in /usr/local/etc/exim/ and make sure it is executable:

CODE:
root@win /usr/local/etc/exim# cat encode
#!/usr/bin/perl
use MIME::Base64;
printf ("%s", encode_base64(eval ""$ARGV[0]""));
root@darkstar /usr/local/etc/exim# chmod +x encode
root@darkstar /usr/local/etc/exim# ls -al encode
-rwxr-xr-x 1 root wheel 85 Apr 23 12:25 encode

Now decide which user account on your server you wish to test ASMTP with. It must be an account you know the password for obviously. I created an account called 'dummy' and set the password to 'dummy' as well - if you do this remember to remove the account or disable it as soon as you've finished testing.

Encode the user:password pair into base64 MIME using the 'encode' script we created above:

CODE:
root@darkstar /usr/local/etc/exim# ./encode "\0dummy\0dummy"
AGR1bW15AGR1bW15

Now enter into Exim's fake SMTP session command-line mode and just for good measure do it in authentication debug mode as well:

CODE:
root@win /root# exim -d+auth -bh 127.0.0.1
Exim version 4.66 (FreeBSD 6.1) uid=0 gid=0 pid=3056 D=fbb95cfd
Probably Berkeley DB version 1.8x (native mode)
Support for: crypteq iconv() IPv6 use_setclassresources PAM Perl OpenSSL Content_Scanning Old_Demime
Lookups: lsearch wildlsearch nwildlsearch iplsearch cdb dbm dbmnz dnsdb dsearch nis nis0 passwd
Authenticators: cram_md5 plaintext spa
Routers: accept dnslookup ipliteral manualroute queryprogram redirect
Transports: appendfile/maildir/mailstore/mbx autoreply lmtp pipe smtp
Fixed never_users: 0
Size of off_t: 8
changed uid/gid: forcing real = effective
 uid=0 gid=0 pid=3056
 auxiliary group list: 0
seeking password data for user "mailnull": using cached result
getpwnam() succeeded uid=26 gid=26
seeking password data for user "root": cache not available
getpwnam() succeeded uid=0 gid=0
configuration file is /usr/local/etc/exim/configure
log selectors = 00000ffc 00089001
trusted user
admin user
changed uid/gid: privilege not needed
 uid=26 gid=6 pid=3056
 auxiliary group list: 6 6
seeking password data for user "mailnull": cache not available
getpwnam() succeeded uid=26 gid=26
originator: uid=0 gid=0 login=root name=Charlie Root
sender address = root@win.munk.me.uk
sender_fullhost = [127.0.0.1]
sender_rcvhost = [127.0.0.1]

**** SMTP testing session as if from host 127.0.0.1
**** but without any ident (RFC 1413) callback.
**** This is not for real!

host in hosts_connection_nolog? no (option unset)
LOG: smtp_connection MAIN
 SMTP connection from [127.0.0.1]
host in host_lookup? yes (matched "*")
looking up host name for 127.0.0.1
DNS lookup of 1.0.0.127.in-addr.arpa (PTR) succeeded
IP address lookup yielded localhost.munk.me.uk
gethostbyname2 looked up these IP addresses:
 name=localhost.munk.me.uk address=::1
 name=localhost.munk.me.uk address=127.0.0.1
checking addresses for localhost.munk.me.uk
 ::1
 127.0.0.1 OK
sender_fullhost = localhost.munk.me.uk [127.0.0.1]
sender_rcvhost = localhost.munk.me.uk ([127.0.0.1])
set_process_info: 3056 handling incoming connection from localhost.munk.me.uk [127.0.0.1]
host in host_reject_connection? no (option unset)
host in sender_unqualified_hosts? no (option unset)
host in recipient_unqualified_hosts? no (option unset)
host in helo_verify_hosts? no (option unset)
host in helo_try_verify_hosts? no (option unset)
host in helo_accept_junk_hosts? no (option unset)
SMTP>> 220 win.munk.me.uk ESMTP Exim 4.66 Wed, 17 Jan 2007 19:24:22 +0000
220 win.munk.me.uk ESMTP Exim 4.66 Wed, 17 Jan 2007 19:24:22 +0000
smtp_setup_msg entered

When you get to this point you are ready to start an SMTP 'conversation' with Exim. First introduce yourself to Exim using the SMTP 'EHLO localhost' command:

CODE:
EHLO localhost
SMTP<< EHLO localhost
sender_fullhost = localhost.munk.me.uk (localhost) [127.0.0.1]
sender_rcvhost = localhost.munk.me.uk ([127.0.0.1] helo=localhost)
set_process_info: 3103 handling incoming connection from localhost.munk.me.uk (localhost) [127.0.0.1]
host in pipelining_advertise_hosts? yes (matched "*")
host in auth_advertise_hosts? yes (matched "*")
host in tls_advertise_hosts? no (option unset)
250-win.munk.me.uk Hello localhost.munk.me.uk [127.0.0.1]
250-SIZE 52428800
250-PIPELINING
250-AUTH PLAIN LOGIN
250 HELP
SMTP>> 250-win.munk.me.uk Hello localhost.munk.me.uk [127.0.0.1]
250-SIZE 52428800
250-PIPELINING
250-AUTH PLAIN LOGIN
250 HELP

In response to your 'EHLO localhost' command, Exim returns more debug information but most importantly for us it also indicates what authentication options it offers in this line:

CODE:
250-AUTH PLAIN LOGIN

This indicates that currently acceptable AUTH methods are PLAIN and LOGIN.

We can then test the PLAIN login method using the "\0dummy\0dummy" user:password pair we encoded above:

CODE:
AUTH PLAIN AGR1bW15AGR1bW15
SMTP<< AUTH PLAIN AGR1bW15AGR1bW15
Running pwcheck authentication for user "dummy"
pwcheck: success (NULL)
plain authenticator:
 $1 =
 $2 = dummy
 $3 = dummy
expanded string: 1
SMTP>> 235 Authentication succeeded
235 Authentication succeeded

This indicates that authentication for 'dummy:dummy' would succeed and mail would be relayed (pending further conditional checks by Exim).

So we now have a working Exim with support for spam/malware checking and authentication over SMTP.

Posted by munk in Email, Ports, Security, Spam at 20:19 | Comments (13) | Trackbacks (0)

Monday, January 15. 2007

Cursor Artifacts Using nv nVidia drivers on X

Just come across an annoying problem whilst using a GeForce 6200 in X - in Firefox, scrolling around inside form fields or the URL bar with the arrow keys results in a number of cursor artifacts left behind making reading or editing anything in those areas impossible. Switching focus away and then back to the Firefox window removes the artifacts, but this isn't very practical.

After some digging around to confirm the bug is with the 'nv' driver (the problem disappears when running with just the vesa driver), I scanned the bugs listed for the nv driver and thankfully found the bug listed already here.

The bug report also thankfully had a simple workaround to the problem - adding:

CODE:

Option "XaaNoSolidFillRect"

in the card's device section. No idea what the drawbacks are to using this option, searching for the term "XaaNoSolidFillRect" just comes up with a list of other nv bug reports citing the above as a solution. From those results, the same problem is described in more detail also at this URL by another nv user with an ascii art representation of the problem (woot!):

http://lists.debian.org/debian-x/2006/01/msg00056.html

Posted by munk in Hardware, X Window System at 12:26 | Comments (0) | Trackbacks (0)

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Wednesday, January 17. 2007

Installing Exim, SASLAuthd, ClamAV and SpamAssassin on FreeBSD 6.2

Monday, January 15. 2007

Cursor Artifacts Using nv nVidia drivers on X