/usr/share/doc/sanitizer/sanitizer.html

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
<html><head><title>The Anomy Sanitizer manual</title></head>
<BODY 
    BGCOLOR="#FFFFFF" 
    TEXT="#005500" 
    LINK="#880000" 
    ALINK="#880000"
    VLINK="#880000">    
<a name="top">

<h1>WARNING:</h1>

<p>This document is outdated!  Please refer to the CHANGELOG for up-to-date
information on new features.</p>

<h1>The <a href="http://mailtools.anomy.net/">Anomy</a> Sanitizer</h1>

<p>
    This file is slowly turning into the Anomy sanitizer's user manual.
    The document is organized so that it makes sense to start at the
    beginning, and read continuously until you reach the mailer-specific
    configuration chapters.  From that point on, everything is optional,
    read what interests you.  Well... the 
    <a href="#feedback">feedback chapter</a> isn't really optional. 
    Read it. <tt>:-)</tt>
</p>

<p>
<ul>
<li>    <a href="#general">Introduction</a>
<li>    <a href="#requirements">Requirements</a>
<li>    <a href="#install">Installation, testing</a>
<li>    <a href="#config">Configuration</a>
<ul>
<li>    <a href="#conf-polvir">Policies and virus scanners</a>
<li>    <a href="#conf-messages">Customizing messages</a>
<li>    <a href="#conf-recommendations">Recommendations</a>
<li>    <a href="#conf-real">A real-world configuration</a>
</ul>
<li>    In-transit sanitizing
<ul>
<li>    <a href="#in-transit-sendmail">sendmail</a>
<li>    <a href="#in-transit-qmail">qmail</a>
<li>    <a href="#in-transit-others">others</a>
</ul>
<li>    Performance
<ul>
<li>    <a href="#perf-cpu">CPU</a>
<li>    <a href="#perf-memory">Memory</a>
</ul>
<li>    Miscellanious hints / FAQs
<ul>
<li>    <a href="#mh-scanner-codes">Virus scanning doesn't work!</a>
<li>    <a href="#mh-anomy-env">The testcases succeed, but I can't run the Sanitizer!</a>
<li>    <a href="#mh-anomy-env">What is the ANOMY environment variable for?</a>
<li>    <a href="#pf-solaris-procmail">Solaris and procmail</a>
<li>    <a href="#pf-postfix">Incoming mail and Postfix</a>
<li>    <a href="#mh-memory-hog">Large messages and memory consumption</a>
<li>    <a href="#mh-html-uuencode">Corrupt attachments from Outlook users</a>
<li>    <a href="#mh-style-tag">Ugly HTML mail from Outlook users</a>
</ul>
</ul>
</p>

<p>
<ul>
<li>    <a href="#hacking">Hacking the Anomy sanitizer</a>
<ul>
<li>    <a href="#hack-design">Basic design</a>    
<li>    <a href="#hack-streams">Why treat the mail as a stream?</a>
<li>    <a href="#hack-cruft">Rough edges</a>
<li>    <a href="#hack-standards">Standards</a>
</ul>
</ul>
</p>

<p>
<ul>
<li>    <a href="#feedback">Feedback</a>
<li>    <a href="#credits">Credits &amp; GPL</a>
</ul>
</p>

<!-- ---------------------------------------------------------------------- -->
<a name="general"><hr><h2>    Introduction    </h2>

<p>
    The Anomy sanitizer is what most people would call "an email virus
    scanner". That description is not totally accurate, but it does cover
    one of the more important jobs that the sanitizer can do for you - 
    <b>it can scan email attachments for viruses</b>.  Other things it can 
    do:
</p>
<p><ul>
<li>
    Disable potentially dangerous HTML code, such as javascript, within
    incoming email.
<li>
    Protect you from email-based break-in attempts which exploit bugs in
    common email programs (Outlook, Eudora, Pine, ...).
<li>
    Block or "mangle" attachments based on their file names.  This way if 
    you don't <i>need</i> to recieve e.g. visual basic scripts, then you
    don't have to worry about the security risk they imply (the ILOVEYOU
    virus was a visual basic program).  This lets you protect yourself and
    your users from whole classes of attacks, without relying on complex, 
    resource intensive and <i>outdated</i> virus scanning solutions.
</ul></p>
<p>
    The sanitizer is designed not to waste important system resources 
    (<a href="#perf-cpu">CPU</a>, <a href="#perf-memory">memory</a>, disk
    space) unnecessarily, and does so by treating it's input as a stream
    which is scanned and rewritten a little bit at a time.
</p>
<p>
    One of the core ideas behind the design of the sanitizer, is that just
    because a message contains an infected attachment doesn't mean that the
    rest of it shouldn't be delivered.  Email often contains important
    information, and it is vital that a tool like this interrupt the normal
    flow of communication as little as possible.  It's common courtesy to
    <a href="#conf-messages">inform the user</a> of any changes that are 
    made.  The Anomy sanitizer tries to follow these rules.
</p>
<p>
    The sanitizer is based on solid foundations - most of the ideas
    implemented in the first versions of the sanitizer were ported from John
    D. Hardin's
    "<a href="http://www.impsec.org/email-tools/procmail-security.html">email
    security through procmail</a>" package.  The sanitizer, like the code it
    is based on, is <b>Free Software</b> in the 
    <a href="http://www.gnu.org/">GNU</a> sense of the term - the sanitizer
    may be modified and redistributed according to the terms of the GNU 
    General Public License.
</p>
<p>
    The following is a random sample of the attacks that are blocked by
    the Anomy sanitizer in it's most common configurations (as of release
    1.28):
</p>
<p><ul>

<li><a href="http://www.securityfocus.com/frames/?content=/vdb/bottom.html%3Fvid%3D1899"
    >Microsoft Windows 2000 ActiveX Control Buffer Overflow Vulnerability</a> 

<li><a href="http://www.securityfocus.com/frames/?content=/vdb/bottom.html%3Fvid%3D1869"
    >Microsoft Exchange Server Invalid MIME Header charset = "" DoS 
    Vulnerability</a> 

<li><a href="http://www.securityfocus.com/frames/?content=/vdb/bottom.html%3Fvid%3D1718"
    >Microsoft Internet Explorer / Outlook Express GetObject() File Disclosure 
    Vulnerability</a> 

<li><a href="http://www.securityfocus.com/frames/?content=/vdb/bottom.html%3Fvid%3D1709"
    >Pine "From:" Buffer Overflow Vulnerability</a> 

<li><a href="http://www.securityfocus.com/frames/?content=/vdb/bottom.html%3Fvid%3D1481"
    >Microsoft Outlook / Outlook Express GMT Field Buffer Overflow 
    Vulnerability</a> 

<li><a href="http://www.securityfocus.com/frames/?content=/vdb/bottom.html%3Fvid%3D1394"
    >Microsoft Internet Explorer and Outlook/Outlook Express Remote File 
    Write Vulnerability</a> 
    
<li><a href="http://www.securityfocus.com/frames/?content=/vdb/bottom.html%3Fvid%3D1285"
    >ITHouse Mail Server 1.04 Buffer Overflow Vulnerability</a> 
    
<li><a href="http://www.securityfocus.com/frames/?content=/vdb/bottom.html%3Fvid%3D1034"
    >Microsoft Clip Art Buffer Overflow Vulnerability</a> 
    
<li><a href="http://www.securityfocus.com/frames/?content=/vdb/bottom.html%3Fvid%3D962"
    >MS Outlook Express 5 Javascript Email Access Vulnerability</a> 
    
<li><a href="http://www.securityfocus.com/frames/?content=/vdb/bottom.html%3Fvid%3D775"
    >Microsoft ActiveX CAB File Execution Vulnerability</a> 
    
<li><a href="http://www.securityfocus.com/frames/?content=/vdb/bottom.html%3Fvid%3D1754"
    >Microsoft Virtual Machine com.ms.activeX.ActiveXComponent Arbitrary 
    Program Execution Vulnerability</a> 
    
<li><a href="http://www.securityfocus.com/frames/?content=/vdb/bottom.html%3Fvid%3D1502"
    >Microsoft Outlook Express Persistent Mail-Browser Link Vulnerability</a> 
    
<li><a href="http://www.securityfocus.com/frames/?content=/vdb/bottom.html%3Fvid%3D1195"
    >Microsoft Outlook 98 / Outlook Express 4.x Long Filename Vulnerability</a> 
  
<li><a href="http://www.securityfocus.com/frames/?content=/vdb/bottom.html%3Fvid%3D125"
    >Multiple Vendor Buffer Overflow in MIME-aware Mail and News Clients 
    Vulnerability</a> 
    
</ul></p>
<p>
    In all cases the above exploits are blocked by some sort of generic
    mechanism which will prevent a number of related attacks against similar
    software with similar problems. This list doesn't include the
    more common low-tech trojan-horse/social engineering attack methods
    which are best handled with user education and an automatically
    enforced attachment policy.
</p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="requirements"><hr><h2>    Requirements    </h2>

<p>
    The Anomy sanitizer is developed on a RedHat Linux system running
    Perl 5.005_03.  Any newer version of Perl on a Unix platform should
    work fine.  The sanitizer has very modest module requirements, and
    only needs the following Perl modules to be present on your system:
</p>
<p><ul>
<li>    MIME::Base64
<li>    MIME::QuotedPrint
</ul></p>
<p>
    Consult your perl documentation (hint: "man CPAN") for information on
    how to install these if you haven't already.
</p>
<p>
    The sanitizer makes no assumptions about what mailer you are using - it
    has been configured to work well with 
    <a href="#in-transit-sendmail">sendmail</a> and 
    <a href="#in-transit-qmail">qmail</a>, and it should be relatively
    easy to <a href="#in-transit-others">get it to work with others</a>, 
    such as postfix or exim.
</p>
<p>
    For testing purposes, it may be a good idea to invoke the sanitizer from
    within <a href="http://www.procmail.org/">procmail</a>, since
    procmail does a very good job of recovering mail if the sanitizer
    panics (e.g. because of an invalid configuration file) and can easily be
    configured to keep backup copies of all processed messages.
</p>
<p>
    If you want to scan attachments for viruses, you will need a third party
    virus scanner which can be invoked from the command line to scan a
    single file.  The virus scanner must return an exit code describing
    whether the file is infected or not, and may optionally also use exit
    codes to indicate that the file was successfully disinfected.
</p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="install"><hr><h2>    Installation, testing    </h2>

<p>
    Download the most recent sanitizer from the web and install all the 
    <a href="#requirements">prerequisites</a>.  The sanitizer can be
    downloaded from it's home page,
    <a href="http://mailtools.anomy.net/">mailtools.anomy.net</a>.
<p>
    Unpack the tarball somewhere on your system, e.g. in <tt>/usr/local/</tt>
    or your home directory.  It will create a directory named <tt>anomy/</tt>
    which will contain this file and a directory named <tt>bin/</tt> 
    containing the sanitizer itself and the MIME parsing module it depends on.
</p>
<p>
    Next, you should run the included test cases to make sure that the 
    sanitizer functions properly on your system.  Enter the
    <tt>anomy/testcases</tt> directory, and give the command
    <tt>./testall.sh</tt>.  This will perform all included tests, and
    compare their results to files named <tt>test-name.ok</tt> in the
    subdirectory named results.def.  You can examine these files to see how
    the sanitizer alters email.  If a test fails, a <tt>test-name.diff</tt>
    file is created which shows the difference between the expected value
    and the test result.  Empty lines are usually harmless, but any other
    failures should be reported back to the author.
</p>
<p>
    If you cannot figure out why a test failed and wish to submit a bug
    report, please include information about your operating system and a
    copy of the relevant <tt>test-name.failed</tt> file.   If all tests 
    succeed, then the sanitizer is ready to be used.
</p>
<p>
    To test the sanitizer on one of your own messages, you can invoke the it 
    from the command line, like this (bourne shell syntax):
</p>
<p></p><font color=#000000><pre>
    $ cd /path/to/anomy
    $ export ANOMY=/path/to/anomy
    $ ./bin/sanitizer.pl &lt; /path/to/message |more
</pre></font>
<p>
    This is an excellent way to test your first configuration file, simply
    add the path to your configuration file to the command line invoking the
    sanitizer, as the first argument:
</p>
<p></p><font color=#000000><pre>
    $ ./bin/sanitizer.pl /etc/sanitizer.cfg &lt; /path/to/message |more
</pre></font>
<p>
    For a more extended test, you may want to sanitize only a single user's
    mail until you are comfortable with the tool.  How this is done depends
    on your mailer, but one common case (sendmail and procmail) is very
    simple.  Just add the following lines to the user's <tt>.procmailrc</tt> 
    file:
</p>
<p></p><font color=#000000><pre>
   :0 c
   backup-mailbox

   ANOMY=/path/to/anomy/
   :0 fw
   |/path/to/anomy/bin/sanitizer.pl
</pre></font>
<p>
    The first rule creates a backup of all messages, in a mailbox named
    <tt>backup-mailbox</tt>.  Since you will probably make mistakes as you
    define your first policy, this is probably a good idea in case the
    sanitizer mistakenly destroys your mail.  The second rule passes the
    messages through the sanitizer, using procmail's filter feature,
    possibly rewriting the message to deactivate virii, trojans, etc.
</p>
<p>
    If you had created a configuration file named
    <tt>/path/to/sanitizer.cfg</tt>, then the sanitization rule would be 
    modified to read as follows:
</p>
<p></p><font color=#000000><pre>
   :0 fw
   |/path/to/anomy/bin/sanitizer.pl /path/to/sanitizer.cfg
</pre></font>
<p>
    Note that this is a completely valid way to invoke the sanitizer - if
    your system administrator won't install it globally, but you have access
    to your <tt>.procmailrc</tt> file, you can simply sanitizer your own mail
    in this fashion.  Also, instead of putting those rules in a 
    <tt>.procmailrc</tt> file, you can put them in <tt>/etc/procmailrc</tt>
    instead and thus sanitize all mail delivered to local users.
<p>
</p>
    <a href="http://www.procmail.org/">Procmail</a> is an excellent tool, and 
    it can be configured to work with most popular MTAs, including 
    <a href="http://www.sendmail.org/">sendmail</a>,
    <a href="http://www.postfix.net/">postfix</a>,
    <a href="http://www.qmail.org">qmail</a> and
    <a href="http://www.exim.org/">exim</a>.  Using procmail is
    probably the easiest way to take advantage of the sanitizer.  
</p>
<p>
    <b>Note</b>:  The above recipies may not be sufficient to get the 
    sanitizer to work on your platform - if you have problems, please be 
    sure to check the <a href="http://mailtools.anomy.net/sanitizer.html"
    >newest version</a> of this manual for platform specific instructions,
    as well as the <b>procmail(1)</b>, <b>procmailrc(1)</b> and 
    <b>procmailex(1)</b> man pages.  Of particular interest when debugging 
    procmail related problems are the <tt>LOGFILE</tt> and <tt>VERBOSE</tt>
    directives.  Also be sure to check the <tt>contrib/</tt> directory of
    the distribution for user-contributed tips and tricks.
</p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="config"><hr><h2>Configuration</h2>

<p>
    Most of the policies and messages generated by the sanitizer can be
    customized.  The sanitizer understands a single configuration syntax,
    accepting configuration commands either on a line-by-line basis from one
    or more text files, or via command-line arguements (each arguement
    corrosponding to one line from a file).  A simple configuration file
    might look like this:
</p>
<p></p><font color=#000000><pre>
   # this is a comment, bla bla
   #
   feat_log_stderr = 1      # enable logging to stderr
   feat_log_inline = 0      # disable logging in the message itself
   feat_trust_pgp = 1       # trust signed or encrypted messages
   
   # Disable most of the advertisements the sanitizer would otherwise
   # put in the header, replace them with our own bogus ones.
   #
   header_info = X-Virus-Scanned: Secured by FooCorp RealSecure MailWall
   header_info += \nX-Garbage: \# this is not a comment # but this is
   header_url = 0
   header_rev = 0

   # Include more configuration...
   #
   /path/to/policy/configuration/file
   /path/to/another/configuration/file
</pre></font>
<p>
    And could be activated like this:
</p>
<p></p><font color=#000000><pre>
    $ sanitizer.pl /path/to/configuration/file
</pre></font>
<p>
    The first setting (logging to standard error) could also have been
    activated with this command line:
</p>
<p></p><font color=#000000><pre>
    $ sanitizer.pl "feat_log_stderr = 1"
</pre></font>
<p>
    The quotation marks are important, otherwise the shell would pass
    "feat_log_stderr", "=" and "1" to the sanitizer as seperate arguements,
    which wouldn't work.  Please resist the urge to create configuration
    files with have '='-signs in their names.
</p>
<p>
    Configuration files may be nested arbitrarily, but to prevent infinite
    loops the sanitizer will by default stop reading after 5 levels of
    nesting.  This maximum recursion level may be altered by setting the
    "max_conf_recursion" variable.
</p>
<p>
    Giving the sanitizer a bogus arguement will make it print an error
    message and the current configuration to standard error.  Appending a
    nonsensical arguement to your normal command line will thus allow you to
    compare the sanitizer's actual configuration with what you had in mind.
</p>
<p>
    The example in the next section displays the complete list of
    configuration variables.  An effort will be made not to break
    compatibility in future releases, although new variables will certainly
    be introduced as the program evolves.
</p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="conf-polvir"><hr><h2>Configuration - Policies and virus scanners</h2>

<p>
    The Anomy sanitizer can process any attachments using a third party
    virus scanner.  Whether a virus scanner is used, and how it's results
    are interpreted depends on the rules defined by the administrator.
</p>
<p>
    Rules are defined by a set of policies.  Each policy is assumed to apply
    to all attachments not matching any previous policy, and whose file name
    matches the policy's regulaur expression.  The policies enforced can be
    "accept", "defang", "mangle", "save" and "drop" in order of increasing
    strictness.  In addition, the "unknown" policy will tell the sanitizer
    to check the next rule.  The panic policy has been depraciated and is
    (for backwards compatibility) equivalent to the "drop" policy.
</p>
<p>
    Attachments which are accepted aren't altered at all.  The defang and
    mangle policies effect the attachment's file name, with mangle
    destroying the original file name completely.  The save and drop
    policies will remove the attachment from the message, replacing it with
    a text message.  With drop the attachment will be deleted, with save it
    will be left on the sanitizer's host file system for examination by an
    administrator.  If the policy is unknown, the attachment will be
    compared with other, lower-priority policies.
</p>
<p>
    Appending an exclamation mark (!) to a policy will make it have the
    side-effect of increasing the internal "bug score" past the "score_bad"
    value, causing the program to return with a non-zero exit code.
</p>
<p>
    An example follows, illustrating most of the stuff involved in defining
    a policy.  Please note that this isn't necessarily a /good/ policy, it's
    just an example.
</p>
<p></p><font color=#000000><pre>
 #
 # These are the default values for all feature switches.
 #
 feat_verbose = 1    # Warn user about unscanned parts, etc.
 feat_log_inline = 1 # Inline logs: 0 = Off, 1 =  Maybe, 2 = Force
 feat_log_stderr = 1 # Print log to standard error
 feat_log_xml = 0    # Don't use XML format for logs.
 feat_log_trace = 0  # Omit trace info from logs.
 feat_log_after = 0  # Don't add any scratch space to part headers.
 feat_files = 1      # Enable filename-based policy decisions.
 feat_force_name = 0 # Force all parts (except text/plain and
                     # text/html parts) to have file names.
 feat_boundaries = 0 # Replace all boundary strings with our own
                     # NOTE:  Always breaks PGP/MIME messages!
 feat_lengths = 1    # Protect against buffer overflows and null
                     # values.
 feat_scripts = 1    # Defang incoming shell scripts.
 feat_html = 1       # Defang active HTML content.
 feat_webbugs = 0    # Web-bugs are allowed.
 feat_trust_pgp = 0  # Don't scan PGP signed message parts.
 feat_uuencoded = 1  # Sanitize inline uuencoded files.
 feat_forwards = 1   # Sanitize forwarded messages
 feat_testing = 0    # This isn't a test-case configuration.
 feat_fixmime = 1    # Fix invalid MIME, if possible.
 feat_paranoid = 0   # Don't be excessively paranoid about MIME headers etc. 
 #
 # Scoring
 #
 score_bad = 100     # Any message requring this many modifications
                     # will cause the sanitizer to return a non-zero
		     # exit code after processing the entire message.
 #
 # You may need to increase the following if you have a very
 # complex configuration split between multiple files.
 #
 max_conf_recursion = 5    # The default is 5.
 #
 # Create temporary or saved files using this template.
 # An attachment named "dude.txt" might be saved as 
 #
 #  /var/quarantine/att-dude-txt.A9Y
 #
 # Note:  The directory must exist and be writable by
 # the user running the sanitizer.
 #
 file_name_tpl = /var/quarantine/att-$F.$$$

 # We have three policies, in addition to the default which is
 # to defang file names.
 #
 file_list_rules = 3
 file_default_policy = defang
 file_default_filename = unnamed.file
   
 # Delete obviously executable attachments.  This list is VERY
 # incomplete!  This is a perl regular expression, see "man 
 # perlre" for info.  The (?i) prefix makes the regexp case 
 # insensitive.
 #
 # There is only one policy, since we aren't using an external
 # scanner.  The file list is split accross two lines, for fun.
 #
 file_list_1  = (?i)\.(exe|com
 file_list_1 += |cmd|bat)$
 file_list_1_policy = drop
 file_list_1_scanner = 0

 # Scan mp3 files for Evil Viruses, using the imaginary mp3virscan
 # utility.  Always define FOUR potential policies, which depend on the
 # exit code returned by the scanner.  Which code means what is 
 # defined in the scanner line, which must contain THREE entries.
 # The fourth policy is used for "anything else".
 #
 #   "accept" if the file is clean (exit status 0 or 1)
 #   "mangle" if the file was dirty, but is now clean (2 or 4)
 #   "drop"   if the file is still dirty (66)
 #   "save"   if the mp3virscan utility returns some other exit code
 #            or an error occurs.
 #
 file_list_2 = (?i)\.(mp3|mp2|mpg)$
 file_list_2_policy = accept:mangle:drop:save
 file_list_2_scanner = 0,1:2,4:66:/path/to/mp3virscan -opt -f %FILENAME

 # Scan WinWord and Excel attachments with built-in macro scanner.
 # We consider anything exceeding the score of 25 to be dangerous,
 # and save it in the quarantine.
 #
 file_list_3 = (?i)\.(doc|dot|xls|xlw)$
 file_list_3_policy = accept:accept:save:save
 file_list_3_scanner = 0:1:2:builtin/macro 25
</pre></font>
<p>
    This probably needs to be documented better - if you are brave, you can
    try reading the comments in <tt>sanitizer.pl</tt> and/or
    <tt>bin/Anomy/Sanitizer.pm</tt> to get a better idea 
    of how this works.  The text messages used to replace dropped or saved 
    attachments can be customized by setting the msg_file_save and 
    msg_file_drop variables.
</p>
<p>
    Note that these rules don't apply to message parts without file names,
    such parts are either treated as plain text, HTML, or left alone.  In
    the future policies based on MIME types or "magic" guessing might be
    added to the sanitizer.
</p>
<p>
    Please send me information about how to configure different
    file_list_N_scanner lines for use with the commercial virus scanners out
    there!
</p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="conf-messages"><hr><h2>Configuration - Customizing messages</h2>

<p>
    All messages, except for the sanitizer log file can be customized
    from within a sanitizer configuration file.  An example:
</p>
<p></p><font color=#000000><pre>
 #
 # Add two lines of informational headers to each message.
 #
 header_info  = X-Sanitizer: Gotcha!
 header_info += \nX-Gotcha: Sanitizer!
 #
 # Disable these builtin headers.
 #
 header_url = 0
 header_rev = 0
 #
 # Replace the "DEFANGED" string with "FIXED".  This 
 # string is used to mangle file names, HTML and other 
 # stuff within the message, so the user might see it.
 #
 msg_defanged = FIXED
 #
 # Also replace a couple of other similar strings.
 # These are only used by the filename mangling code.
 #
 msg_blacklisted = EVIL
 #
 # Replace the defaults with truly obnoxious messages.
 # These two replace attachments which are dropped or
 # saved.
 #
 msg_file_drop  = *****\n
 msg_file_drop += HA HA, I DROPPED YOUR ATTACHMENT!\n
 msg_file_drop += Now you'll never see %FILENAME again!
 msg_file_drop += *****\n
 #
 msg_file_save  = *****\n
 msg_file_save += Added %FILENAME as %SAVEDNAME to my\n
 msg_file_save += stolen email collection.\n
 msg_file_save += *****\n
 #
 # This is prepended to PGP signed/encrypted message
 # parts, to warn the user.
 #
 msg_pgp_warning = WARNING: Unsanitized content follows.\n
 #
 # Tell the user what's going on.  This prefixes the
 # sanitizer log, which is always in english.
 #
 msg_log_prefix  = This message has been sanitized.  Stuff\n
 msg_log_prefix += may have been altered - the following\n
 msg_log_prefix += log explains what was done and why.\n
 #
</pre></font>
<p>
    Although I can't imagine why you would want to, you can also redefine
    the messages "msg_usage" and "msg_current".  These messages are only
    displayed when you invoke the sanitizer incorrectly at the command line.
</p>
<p>
    If you take advantage of this facility to translate the default messages
    to your language, please consider sharing your translation with me so I
    can include it in future releases of the sanitizer.
</p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="conf-recommendations"><hr><h2>Configuration - Recommendations</h2>

<p>
    In general, I recommend using "defang" as a default policy since keeping
    track of which extensions are executable or scriptable in the windows
    world this week strikes me as a rather daunting task.  Defanging
    (mangling the file names) allows the data to reach the user, but forces
    users to take an extra step and think about what they are doing before
    they can open and work with whatever they were sent.
</p>
<p>
    A policy to "accept" safe extensions such as .gif, .jpg etc can be added
    to make life easier for your users.
</p>
<p>
    Microsoft Office documents, the most common executables, and archives
    (zip etc.) should probably be scanned with a commercial virus scanner.
    If you don't absolutely need to receive executable content via. email,
    consider blocking it entirely.
</p>
<p>
    It is rather important to block Microsoft application/ms-tnef files,
    which are usually named "winmail.dat".  The TNEF encoding is currently
    not understood by the sanitizer, which means it can easily be used to
    smuggle malicious attachments past the sanitizer unless it is blocked.
</p>
<p>
    The default policies coded into the sanitizer try to accept all sorts of
    plain text files, images, audio files, archives and movies.  The most
    common Microsoft documents are scanned by the internal macro scanner,
    and if they exceed a threshold of 25 the attachments are removed and put
    in quarantine. Note that their names are not defanged by default, since
    that would probably get users up in arms.  Anything else is defanged by
    the default policy.
</p>
<p>
    If you are paranoid, don't use the default configuration!
</p>
<p>
    Finally, no matter what your policy - at least <i>try</i> to educate
    your users.  Do this both for security's sake, and to keep people from
    getting mad when their email gets rewritten.  If people know what is
    going on and why, then they are much less likely to complain.
</p>
<p>
    If you intend to use the program regularly, I recommend subscribing to
    the anomy-list mailing list (see the 
    <a href="http://mailtools.anomy.net/">Anomy home page</a> for more
    information).  The traffic is currently very low, and is primarily used
    to announce new versions or warn users of email-related hazards.
</p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="conf-real"><hr><h2>A real-world configuration</h2>

<p>
    The following instructions document a real-world configuration, very
    similar to one currently in use in a production environment, on a
    sendmail mail gateway. Instructions for configuring sendmail itself
    are omitted since they are identical to those covered elsewhere in
    this document.
</p>
<p>
    The configuration itself is stored in <TT>/etc/sanitizer.cfg</TT>, and 
    looks about like this:
</p>
<p></p><font color=#000000><pre>
  # Active features.
  #
  feat_boundaries     = 0
  feat_files          = 1
  feat_forwards       = 1
  feat_html           = 1
  feat_lengths        = 1
  feat_log_inline     = 1
  feat_log_stderr     = 0
  feat_scripts        = 1
  feat_trust_pgp      = 0
  feat_uuencoded      = 1
  feat_verbose        = 1
  file_list_rules     = 4
  #
  # Note:  This directory must exist and be writable by
  # the user running the sanitizer.
  #
  file_name_tpl       = /var/quarantine/att-$F-$T.$$

  # Files we absolutely don't want (mostly executables).
  #
  file_list_1_scanner = 0
  file_list_1_policy  = save
  file_list_1         = (?i)(winmail\.dat
  file_list_1        += |\.(exe|vb[es]|c(om|hm)|bat|pif|s(ys|cr))
  file_list_1        += (\.g?z|\.bz\d?)*)$

  # Pure data, don't mangle this stuff (much).
  #
  file_list_2_scanner = 0
  file_list_2_policy  = accept
  file_list_2         = (?i)\.(gif|jpe?g|pn[mg]|x[pb]m|dvi|e?ps|p(df|cx)|bmp
  file_list_2        += |mp[32]|wav|au|ram?
  file_list_2        += |avi|mov|mpe?g
  file_list_2        += |t(xt|ex)|csv|l(og|yx)|sql|jtmpl
  file_list_2        += |[ch](pp|\+\+)?|s|inc|asm|pa(tch|s)|java|php\d?
  file_list_2        += |[ja]sp
  file_list_2        += |can|pos|ux|reg|kbf|xal|\d+)(\.g?z|\.bz\d?)*$

  file_list_3_scanner = 0
  file_list_3_policy  = accept
  file_list_3         = ^[^\.]+$

  # Archives and scriptable stuff - virus scan these.
  # NOTE:  There must be THREE groups of exit codes and FOUR policies,
  #      - the first three match the code groups, the fourth is default.
  #
  file_list_4_scanner = 0:5:3,4:/usr/local/bin/avp.sh %FILENAME
  file_list_4_policy  = accept:accept:save:save
  file_list_4         = (?i)\.(xls|d(at|oc)|p(pt|l)|rtf|[sp]?html?
  file_list_4        += |class|upd|wp\d?|m?db
  file_list_4        += |z(ip|oo)|ar[cj]|lha|[tr]ar|rpm|deb|slp|tgz
  file_list_4        += )(\.g?z|\.bz\d?)*$

  # Default policy: accept, but mangle file name.
  #
  file_default_policy = defang
</pre></font>
<p>
    This policy invokes the <a href="http://www.avp.ru/">AVP</a> virus 
    scanner for common Microsoft document formats and compressed archives. 
    The scanner (<TT>AvpLinux</TT>) is installed in <TT>/usr/local/avp</TT>, 
    and it's virus database is in the subdirectory <TT>avc</TT>. The scanner 
    is invoked by calling the <TT>/usr/local/bin/avp.sh</TT> script, which 
    looks like this:
</p>
<font color=#000000><pre>
  #!/bin/bash

  cd /usr/local/avp/avc
  [ "$1" = "" ] &amp;&amp; exit 21
  [ -f "$1" ] || exit 20
  exec ../AvpLinux -M -P -B -- $1 2&gt;/dev/null &gt;/dev/null
</pre></font>
<p>
    Keeping the virus database in it's own special directory simplifies
    updating it automatically. Such updates can be accomplished by invoking
    a script once a week from cron. My script looks like this:
</p>
<font color=#000000><pre>
  #!/bin/bash
  #
  cd /usr/local/avp/
  rm -rf avc-old
  mkdir avc-update     || exit 1
  cd avc-update        || exit 1

  ncftpget -V -R ftp.avp.ru . '/updates/*' || (echo 'Failed!'; exit 2)

  ../AvpLinux ../infected.doc &gt;/dev/null 2&gt;/dev/null
  [ "$?" != "4" ] &amp;&amp; (echo 'Failed!'; exit 3)

  echo "OK, update complete, activating new files."
  cd ..
  mv avc avc-old &amp;&amp; mv avc-update avc
</pre></font>
</p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="in-transit-sendmail"><hr><h2>In-transit sanitizing - sendmail</h2>
<p>
    The following instructions describe <b>two</b> different methods to
    sanitize in-transit email with sendmail.  This works fine on a mail
    gateway, but if you are just sanitizing mail being delivered to local
    recipients (on the same machine as the sanitizer) then it is far simpler
    and safer to use procmail as your local delivery agent and invoke the
    sanitizer as described in the <a href="#install">installation chapter</a>.
</p>
<p>
    One method involves using procmail as an intermediate layer between
    sendmail and the sanitizer, the other method invokes the sanitizer
    directly.  The procmail method is recommended, since procmail provides
    simple and robust error handling and logging functions.  On the other
    hand, the procmail method may be signifigantly slower, since it involves
    at least twice as many I/O operations and perhaps some disk accesses as
    well.  On an already loaded system, this may not be acceptible overhead.
</p>
<p>
    The choice is yours - but whatever you do <b>be careful</b>, and be sure
    to test this carefully on a non-production machine before implementing
    it anywhere important!  Keep in mind that sendmail is a tricky beast and
    this may not work on your system without lots of modifications.  This
    works for <i>me</i>, but <i>your</i> mileage may vary.
</p>
<p><ol>
<li><p>
    If you <b>are</b> using procmail, skip steps 2. and 3.<br>
    If you <b>are not</b> using procmail, skip steps 4. and 5.
</p>    
<li><p>
    If you <b>are</b> using procmail, <b>skip</b> this step.<br>
    Create the following shell script,  e.g. in 
    <tt>/usr/local/bin/sanitize</tt>.
</p>
<p></p><font color=#000000><pre>
  #!/bin/sh
  #
  export ANOMY=/path/to/anomy
  export CFG=/path/to/sanitizer/configuration
  exec $ANOMY/bin/sanitizer.pl $CFG | /path/to/sendmail -oi -f ${@+"$@"}
</pre></font>
<p>
    Be sure to set all the paths to whatever makes sense on your system.
    Don't forget to make the script executable 
    (<tt>chmod +x /usr/local/bin/sanitize</tt>).
</p>
<li><p>
    If you <b>are</b> using procmail, <b>skip</b> this step.<br>
    Add the following mailer specification to <tt>sendmail.cf</tt>.  It's a 
    good idea to add this to the part of the file containing the <i>other</i>
    mailer definitions.
</p>
<p></p><font color=#000000><pre>
  Msanitize,
     P=/usr/local/bin/sanitize, F=DFMmhu, 
     S=11/31, R=21/31, T=DNS/RFC822/X-Unix, A=sanitize $f $u
</pre></font>
<li><p>
    If you <b>are not</b> using procmail, <b>skip</b> this step.<br>
    Create a procmail configuration file named <b>/etc/sanitizer.rc</b> 
    like this:
</p>
<p></p><font color=#000000><pre>
  # Procmail filter rules for sanitizing email and then resending it.
  # Uncomment the following lines to enable logging or verbose logging.
  # VERBOSE=yes 
  # LOGFILE=/var/log/procmail-sanitizer.log
  
  ANOMY=/path/to/anomy/
  :0 f
  | $ANOMY/bin/sanitizer.pl /path/to/sanitizer/configuration

  :0 
  ! -oi -f "$@"
</pre></font>
<p>
    Be sure to set all the paths to whatever makes sense on your system.
</p>
<li><p>
    If you <b>are not</b> using procmail, <b>skip</b> this step.<br>
    Add the following mailer specification to <tt>sendmail.cf</tt>, if 
    it doesn't exist already.  It's a good idea to add this to the part of 
    the file containing the <i>other</i> mailer definitions.  Be sure to 
    adjust the path to the procmail binary to match your system.
</p> 
<p></p><font color=#000000><pre>
  Mprocmail,
     P=/usr/bin/procmail, F=DFMmShu, 
     S=11/31, R=21/31, T=DNS/RFC822/X-Unix, A=procmail -m $h $f $u
</pre></font>
<li><p>
    Add the following rules to sendmail.cf, either in ruleset 98 (local
    hacks, on RedHat systems) or right before the virtual user stuff in
    ruleset 0:
</p>
<p></p><font color=#000000><pre>
  # Sanitize with procmail:
  #R$* &lt; @test.com. &gt; $* $#procmail $@/etc/sanitizer.rc $:$1&lt;@test.com.CLEAN.&gt;$2
  # Sanitize without procmail:
  #R$* &lt; @test.com. &gt; $* $#sanitize $@anomy $:$1&lt;@test.com.CLEAN.&gt;$2
  R$* &lt; @ $+ .CLEAN. &gt; $*   $1&lt;@$2.&gt;$3
  R$* &lt; @ $+ .CLEAN &gt; $*    $1&lt;@$2.&gt;$3 
                          ^
                           use TABS here!
</pre></font>
<p>
    <b>Notes:</b> Only one of the two .CLEAN rules are necessary -
    which one seems slightly system-dependant.  Having both won't hurt.  Be
    sure to replace "test.com" with the domain for which you want to
    sanitize mail - the example will sanitize all messages destined for
    someone@test.com.  Multiple domains can be specified by repeating the
    first line, once for each domain or by specifying a class of domains, as
    described below.
</p>
<li><p>
    Add the user sendmail runs as, on the mail port, to the list of trusted
    users (the "<tt>t</tt>" class - search <tt>sendmail.cf</tt> for the phrase
    "Trusted users").  This instructs sendmail not to generate a warning
    header when the shell script sets the From-address when it resends the
    sanitized mail.  On RedHat 6.x systems this user is named "mail".  This
    step may not be necessary on some systems, but again, it won't hurt.
</p>
<li><p>
    Finally, activate the sanitizing method you prefer (with or without 
    procmail) by uncommenting (removing the leading <tt>#</tt>-sign) the 
    relevant line added in step 6 and then restart sendmail.
</p>
</ol></p>
<p>
    Please be careful to use TABs where necessary in the <tt>sendmail.cf</tt>
    file.  In the <tt>Msanitize</tt> and <tt>Mprocmail</tt> definitions above,
    the lines have been split to improve readability - either copy the
    entire text into a single line in your <tt>sendmail.cf</tt> or be sure
    that the continuations begin with TAB characters, <b>not</b> spaces.
</p>
<p>
    Although the above instructions all assume you are editing your
    <tt>sendmail.cf</tt> file directly, they can easily be adapted for
    people using the (recommended) m4 method to configure sendmail. Simply
    append the mailer definitions to your m4 file in a section named
    <tt>MAILER_DEFINITIONS</tt>, and the local hacks stuff to a section
    named <tt>LOCAL_RULE_0</tt>.  People interested in m4 configuration 
    might also find the <tt>anomy.m4</tt> and <tt>sendmail-m4.txt</tt> 
    files in the <tt>contrib/</tt> directory of the distribution helpful.
</p>
<p>
    To match a class of domains (instead of just test.com), you could
    replace the first R$* line(s) with something like this:
</p>
<p></p><font color=#000000><pre>
  # Sanitize with procmail:
  #R$* &lt; @ $=w . &gt; $*    $#procmail $@/etc/sanitizer.rc $:$1&lt;@$2.CLEAN.&gt;$3
  # Sanitize without procmail:
  #R$* &lt; @ $=w . &gt; $*    $#sanitize $@anomy $:$1&lt;@$2.CLEAN.&gt;$3
</pre></font>
<p>
    This matches any host names in the "<tt>w</tt>" class (traditionally 
    <tt>/etc/sendmail.cw</tt>).  An "<tt>X</tt>" class can be defined with 
    "<tt>CX host</tt>" or "<tt>FX/path/to/file</tt>" lines near the 
    beginning of the sendmail configuration file.  People using m4
    configuration can add such definitions after the <tt>LOCAL_CONFIG</tt>
    directive in their m4 files.
</p>
<p>
    If you are somewhat reckless (or are sure you know what you are doing), 
    you can just sanitize everything, like this:
</p>
<p></p><font color=#000000><pre>
  # Sanitize with procmail:
  #R$* &lt; @ $+ . &gt; $*    $#procmail $@/etc/sanitizer.rc $:$1&lt;@$2.CLEAN.&gt;$3
  # Sanitize without procmail:
  #R$* &lt; @ $+ . &gt; $*    $#sanitize $@anomy $:$1&lt;@$2.CLEAN.&gt;$3
</pre></font>
<p>
    Please note that sanitizing everything like this is <b>not
    recommended</b>, since it will sanitize both incoming and outgoing email.
</p>
<p>
    It is the author's humble opinion, that incoming and outgoing email
    should be handled in fundamentally different ways; incoming email should
    always be delivered to the recipient, if at all possible (but it's a
    good idea to defang the dangerous bits first), but outgoing email should
    be bounced back to the sender if it contains a virus or security hazard.
    You don't want to send partial messages out of your organization - you
    want to notify the sender so they can fix the problem and re-send the
    content as quickly as possible.  Future revisions of this document will
    describe how to use the Sanitizer to simply block risky outgoing mail.
</p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="in-transit-qmail"><hr><h2>In-transit sanitizing - qmail</h2>

<p>
    The following instructions describe one way to use the Anomy sanitizer
    with qmail to filter in-transit email.  This is not the simplest way
    to sanitize mail destined for local users, but is quite useful on a
    gateway machine.
</p>
<p><ol>
<li><p>
    Install qmail with the qmail-queue-patch and qmail-qfilter.
</p>
<p>
    From <a href="http://www.qmail.org/">qmail.org</a>: "Bruce Guenter has
    written a patch which causes any program that would run qmail-queue to
    look for an environment variable QMAILQUEUE. If it is present, it is
    used in place of the string "bin/qmail-queue" when running qmail-queue.
    This could be used, for example, to add a program into the 
    qmail-smtpd-&gt;qmail-queue pipeline that could do filtering, rewrite 
    broken headers, etc."
</p>
<p>
    This is just what we are going to use. You will find the
    qmail-queue-patch here:
    <a href="http://www.math.ntnu.no/mirror/www.qmail.org/qmailqueue-patch">http://www.math.ntnu.no/mirror/www.qmail.org/qmailqueue-patch</a>
    (and on every other qmail-mirrior site).
</p>
<p>
    qmail-qfilter is found here: 
    <a href="http://em.ca/~bruceg/qmail-qfilter/">http://em.ca/~bruceg/qmail-qfilter/</a>.
</p>

<li><p>
    Install tcpserver (ucspi).
</p>
<p>
    You can find this here: 
    <a href="http://em.ca/~bruceg/rpms/ucspi-tcp/">http://em.ca/~bruceg/rpms/ucspi-tcp/</a>.
</p>
<li>
<p>
    Make tcpserver set the qmail-queue-parameter/variable
</p>
<p>
    This is done by editing the <tt>/etc/tcpcontrol/smtp.rules</tt> file. 
    The file should look something like:
</p>
<p></p><font color=#000000><pre>
 # Myself going through the filter
 127.0.0.1:allow,RELAYCLIENT="",QMAILQUEUE="/var/qmail/filters/smtpd-queue"
 # Server(s) allowed to relay, but not going through the filter
 xxx.xxx.xxx.xxx:allow,RELAYCLIENT=""
 # Default (everyone else must go through)
 :allow,RELAYCLIENT="",QMAILQUEUE="/var/qmail/filters/smtpd-queue"
</pre></font>
<p>
    Compile the file (tcpserver uses a compiled version of this file with a
    .cdb-extension). If you also use qmail-qmqpd or any other
    qmail daemon that receives incoming mail, be sure to edit and
    recompile the corrosponding rule file (e.g.
    <tt>/etc/tcpcontrol/qmqp.rules</tt>) and use the same value for 
    QMAILQUEUE in both (or all) places.
</p>
<p>
    Now you have tcpserver accepting connections, sending the incoming email
    with the QMAILQUEUE-variable set to the script "smtpd-queue".
</p>
<p>
    The script smtpd-queue (or whatever you choose to call it) should look
    something like:
</p>
<p></p><font color=#000000><pre>
#!/bin/sh
exec /usr/bin/qmail-qfilter
    /var/qmail/filters/sanitizer /var/qmail/filters/sanitizer.cfg
</pre></font>
<p>
    Note:  the exec command has been split between lines for readability.
    It should all be in one line.
</p>
<p>
    What happens here is that qmail-qfilter passes the email to sanitizer
    (which starts with a config-file in this example). When sanitizer is
    finished with it, it is passed back qmail so it can be sent the usual
    way.
</p>
<li><p>
    Configure qmail to act as a relay server.
</p>
<p>
    Read the FAQ if you don't know how to do this.
</p>
</ol></p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="in-transit-others"><hr><h2>In-transit sanitizing - others</h2>

<p>
    In general, the sanitizer should be able to work with any mail transfer
    agent that runs on Unix (and with minor tweaks, the sanitizer should be
    able to run just fine on e.g. Windows).
</p>
<p>
    The thing to look for, are filtering hooks in your MTA.  If your MTA has
    a filtering API already defined, then try and get it to spit messages
    out to the sanitizer on standard input and recapture the sanitizer's
    standard output.  If that doesn't work, then you can probably wrap your
    local delivery agent with a shell script that passes messages through
    the sanitizer first.  Use your imagination!  Let me know how it goes.
</p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="perf-cpu"><hr><h2>    Performance - CPU </h2>

<p>
    Perl may not be a very fast language, but if speed isn't critical it is
    a good choice for a program like this, since it has good pattern
    matching facilities and there are no buffer overflows to worry about.
    Implementing the scanner in C or C++ would be somewhat more efficient,
    but would be much harder to make as secure and flexible.
</p>
<p>
    But I still want the script lean enough to be useable on a production
    mail server with lots and lots of traffic.  To achieve this I will try
    to keep the script's CPU usage O(length-of-message) and consumption of
    other resources as close to a constant as possible, so the script will
    scale well. I won't create temporary files unless/until I add support
    for third party virus scanners (like AMaViS has).
</p>
<p>
    I ran a few tests on revision 1.10 to see if my choice of language would
    make these design constraints pointless (basically, I wanted to answer
    the question of whether Perl can do the job or not).
</p>

    <h3>Test data:</h3>

<p>
    The sanitizer was tested on my 525Mhz Celeron (bus OC'ed to 95Mhz), with
    the following messages.
</p>
<p></p><font color=#000000><pre>
file         size         description
---------    ---------    -----------    
Dev.test1         2206    a plain RFC822 message with no attachment
Dev.test2        26227    3 parts:
                            a text part with a UU-encoded evil HTML snippet
                            a html part with evil html
                            a harmless plain text part
Dev.test3         2342    a multipart/signed message containing clean text
Dev.test4        17139    3 parts:
                            a uu-encoded text part
                            a plain text part with an UU-encoded perl script
                            an unencoded perl script (8bit, text/plain)
Dev.test6      4984617    a multipart mixed message with a big base64-encoded
                          jpeg attachment.
</pre></font>

    <h3>Results:</h3>
    
<p></p><font color=#000000><pre>
[bre@diskordiah bin]$ time ./sanitizer.pl &lt;/dev/null
0.10user 0.01system 0:00.10elapsed 101%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (282major+194minor)pagefaults 0swaps

[bre@diskordiah bin]$ time ./sanitizer.pl &lt;../Dev.test1 &gt;/dev/null
0.12user 0.00system 0:00.14elapsed 85%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (287major+201minor)pagefaults 0swaps

[bre@diskordiah bin]$ time ./sanitizer.pl &lt;../Dev.test2 &gt;/dev/null
0.47user 0.00system 0:00.47elapsed 98%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (289major+283minor)pagefaults 0swaps

[bre@diskordiah bin]$ time ./sanitizer.pl &lt;../Dev.test3 &gt;/dev/null
0.13user 0.00system 0:00.12elapsed 101%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (287major+204minor)pagefaults 0swaps

[bre@diskordiah bin]$ time ./sanitizer.pl &lt;../Dev.test4 &gt;/dev/null
0.20user 0.03system 0:00.25elapsed 91%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (288major+223minor)pagefaults 0swaps

[bre@diskordiah bin]$ time ./sanitizer.pl &lt;../Dev.test6 &gt;/dev/null
12.63user 0.05system 0:13.00elapsed 97%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (970major+257minor)pagefaults 0swaps 
</pre></font>

    <h3>What it all means:</h3>

<p>
    The worst case (bytes/sec) is the smallest message, due to the overhead
    of starting perl and compiling the parser (about 0.10 seconds).  This
    case only gives us a throughput of 15Kb/sec (kilobytes/sec), which is
    actually rather appalling (just imagine the case if we were forking 10
    processes, instead of one).
</p>
<p>
    The best case, Dev.text6, has a througput of over 350Kb/sec.  Most of
    the work done in this case is just decoding/copying/encoding the Base64
    attachment, without even examining the contents (it's a jpeg).  The
    decoding and encoding could easily be optimized away for attachments we
    don't intend to sanitize (such as graphics).  So large attachments
    aren't a problem, CPU-wise - not compared to the small messages anyway.
</p>
<p>
    Since someone told me that the average size of email these days is close
    to 20k, then either Dev.test2 (55Kb/sec) or Dev.test4 (68Kb/sec) might
    be representative of the average throughput of the sanitizer on my
    system.
</p>
<p>
    So for any network connection under 1MB/sec (1 megabit), a dual 500Mhz
    PIII should be able to sanitize all the incoming mail, without any
    noticable delays and with cycles to spare - even during peak hours.  If
    you don't mind a slight delay (and aren't expecting any mail bombs...)
    you can probably get away with less hardware, more bandwidth or both.
</p>
<p>
    Is this good enough?  Please <a href="mailto:bre@netverjar.is">let me 
    know</a> what you think.
</p>
<p>
    Since the performance is almost entirely CPU bound, throughput could be
    increased linearly by simply adding more processing power, e.g. by
    adding more or faster CPUs to your mail server, or by creating a
    sanitizer farm.
</p>
<p>
    Another method to speed things up would be to change the sanitizer into
    some sort of daemon, thus avoiding the startup- and compilation costs of
    perl entirely.  Since initialization accounts for 25-45% of the time it
    takes to process the "average message", and over 75% of the time for the
    small messages (which are very common), this would make quite a
    difference.
</p>
<p>
    OTOH, the performance is only going to get worse, once external virus
    scanners are added to the mix...
</p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="perf-memory"><hr><h2>    Performance - Memory </h2>

<p>
    <b>Note:</b> <a href="#mh-memory-hog">read this</a> if you are having 
    problems with excessive memory consumption when sanitizing very large 
    messages.
</p>
<p>
    While scanning the big message (Dev.test6), top consistantly reported
    memory usage as (SIZE, RSS, SHARE) = (2084, 2084, 1052).  For Dev.test4
    the numbers were (1952, 1952, 1056) and for Dev.test1 they were (1860,
    1860, 1052).
</p>
<p>
    The difference is probably due to Dev.test6 maxing out all the IO
    buffers it had available, which the other tests were too small to do.  I
    verified this theory by tripling the size of Dev.test6 - the resulting
    numbers were almost identical (2088 instead of 2084).  Cool!
</p>
<p>
    This doesn't mean that more memory usage is impossible - the sanitizer
    allocates a new set of buffers for each level of nesting within the
    message. A memory DoS attack could be launched by deeply nesting
    uuencoded parts within each other - this could at the moment raise the
    memory (and CPU) usage arbitraily.  But this would be a deliberate
    attack, such messages are rarely, if at all, created by normal mailers.
</p>
<p>
    This could be addressed by adding a maximum recursion limit to the
    sanitizer, but I haven't done so yet and am not sure it's necessary.
    Aren't there easier ways to attack a mail server?
</p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="mh-scanner-codes"><hr><h2>Virus scanning doesn't work!</h2>

<p>
    The most common reason people have a hard time getting external virus 
    scanners to work, is they enter incorrect <tt>file_list_N_scanner</tt>
    and/or <tt>file_list_N_policy</tt> lines.
</p>
<p>
    There must be <b>four</b> policies, and <b>three</b> groups of exit
    codes, otherwise the scan won't work.  The rationale for having three
    code groups and four policies is that virus scan results fall into the
    following categories:
</p>
<p>
<ol>
<li> Clean files - no infections found.
<li> Cleaned files - infectiosn found but were successfully disinfected.
<li> Infected files - unremovable infections were found.
<li> Errors.
</ol>
</p>
<p>
     The <a href="#conf-real">real world configuration</a> example illustrates
     this.
</p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="mh-anomy-env"><hr><h2>The testcases succeed, but I can't run the sanitizer!<br>
			       What is the ANOMY environment variable for?</h2>

<p>
    The ANOMY environment tells the Sanitizer script where to look for 
    it's modules, MIMEStream.pm and Sanitizer.pm.  Unless it is set, the 
    Sanitizer won't run.  The test cases all set this variable properly,
    which is why they succeed even though you can't run it yourself.
</p>
<p>
    Alternatives:
<ul>
<li>Add the <tt>/path/to/anomy/bin/</tt> directory to
    your PERL5LIB environment variable in some global place such as
    <tt>/etc/profile</tt>.
<li>Add a symbolic link to some other directory normally searched by Perl 
    for libraries.  The symbolic link should be named "Anomy" and should 
    link to <tt>/path/to/anomy/bin/Anomy/</tt> directory.
</ul>   
</p>
<p>
    Which method is best is simply a matter of taste.
</p>

<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="pf-solaris-procmail"><hr><h2>    Solaris and Procmail </h2>

<p>
    A few users have reported that to get the Sanitizer to work from 
    within procmail on Solaris the following lines must be added either
    to <tt>/etc/procmailrc</tt> or the <tt>.procmailrc</tt> file which
    invokes the sanitizer:
</p>
<p></p><font color=#000000><pre>
 PATH="/usr/bin:$PATH"
 SHELL=/bin/sh
</pre></font>
<p>
    Special thanks to <b>Peter Burkholde</b> for his detailed feedback.
</p>

<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="pf-postfix"><hr><h2>    Incoming mail and Postfix </h2>

<p>
Patrick Duane Dunston 
&lt;<a href="mailto:duane@duane.yi.org">duane@duane.yi.org</a>&gt; and
Bill Kenworthy contributed a short how-to on configuring Postfix to 
filter messages through the sanitizer before delivery.  Their instructions 
may be found in the <tt>contrib/</tt> directory of the program distribution.
</p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="mh-memory-hog"><hr><h2>Large messages and memory consumption</a></h2>

<p>
    Some people have reported problems with very large messages 
    and excessive memory consumption when invoking the sanitizer from within
    procmail.  These problem is caused by procmail, not the sanitizer.  If 
    you have this problem, consider limiting incoming message size to
    something that will fit in your mail server's memory or invoking the 
    sanitizer directly (without procmail).
</p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="mh-html-uuencode"><hr><h2>Corrupt attachments from Outlook users</a></h2>

<p> <b>Q:</b> <i>
    My problem is that attachments from Exchange/Outlook users get
    corrupted. The end result is that the document is completely unreadable
    when detached. One of the symptoms is that it ends up with the word
    "DEFANGED" being inserted into the body of the attachment:
<ul>
<tt>M````````````````&gt;&lt;DEFANGED.35 M`````````````````````````</tt>
</ul>
</i></p>
<p> <b>A:</b>
    This is HTML defanging, defanging the contents of an UU-encoded
    attachment.  This only happens when the following conditions are all
    met:
    <ol>
    <li> Users send attachments UU-encoded, instead of using the standard
         MIME encoding.
    <li> HTML defanging is on (feat_html=1).
    <li> UUencoded attachment support is off (feat_uuencoded=0).
    </ol>
</p>
<p>
    The solution is to turn on uuencoded attachment support, or turn off
    HTML defanging.  The latter is not recommended.
</p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="mh-style-tag"><hr><h2>Ugly HTML mail from Outlook users</a></h2>

<p>
    <b>Note:</b> This problem was hopefully solved when the HTML cleanup 
    code was rewritten for revision 1.45 of the sanitizer.
</p>
<p> <b>Q:</b> 
    <i>I'm not sure if this is a bug per se, but mail received 
    from Outlook XP using Word as the editor in HTML format looks very ugly.  
    I've attached an example.  I'm using anomy 1.35.  I'd really appreciate 
    any hints on how to configure or patch anomy to handle this!</i>
</p>
<p> <b>A:</b>
    This is a known issue with the sanitizer, inherited from John
    Hardin's procmail ruleset.
</p>
<p>     
    It has to do with the defanging of &lt;STYLE&gt;...&lt;/STYLE&gt; 
    blocks, which were invented by someone with no clue of HTML design 
    philosopy.  Instead of the style settings being attributes or "funny 
    tags" they are simply written out as a CSS definition following the 
    &lt;STYLE&gt; tag - when the &lt;STYLE&gt; tag gets defanged, the CSS 
    info is revealed as text where it used to be invisible.
</p>
<p>
    The reason this is all so stupid is <i>the exact same thing happens</i>
    if the un-defanged HTML is viewed in a browser that doesn't know about
    STYLE tags.
</p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="hacking"><hr><h2>Hacking the Anomy sanitizer</h2>

<p>
    These are short introductory chapters, for those interested in hacking
    on the Anomy sanitizer.  The source code is somewhat commented, but it's
    probably pretty hard to grasp the overall organization of the code by
    jumping right in.  So start here. :-)
</p>
<p><ul>
<li>    <a href="#hack-design">Basic design</a>    
<li>    <a href="#hack-streams">Why treat the mail as a stream?</a>
<li>    <a href="#hack-cruft">Rough edges</a>
<li>    <a href="#hack-standards">Standards</a>
</ul></p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="hack-design"><hr><h2>Hacking - Basic design</h2>

<p>
    The sanitizer is built around my MIMEStream (Anomy::MIMEStream) module,
    which lives in the <tt>anomy/bin/Anomy/</tt> directory.  This module was
    designed to allow parsing and editing of arbitrarily complex MIME
    streams.  It contains facilities for decoding MIME streams, as well as
    routines for rebuilding or creating such streams from scratch.
</p>
<p>
    The MIMEStream module contains a MIME parsing engine which interprets
    the basic RFC822/MIME structure of the message and hands each part to a
    handler provided by the application using it (in this case the
    sanitizer).
</p>
<p>
    Handlers are selected based on the MIME-type of the given part.  At
    initialization, the sanitizer registers it's handlers with the parsing
    engine, and then essentially says "Go forth and parse" - and that's
    that. The actual flow of the program is controlled by MIMEStream, but
    most of the work takes place within the part handlers.
</p>
<p>
    Each handler makes use of Read() and Write() functions provided by the
    parser engine, to read the decoded message part, possibly modify it, and
    send the results back to the parser.  The parser re-encodes the data and
    ultimately sends the results to the output stream.  The Read() and
    Write() functions hide all buffering, decoding and encoding involved in
    "stream editing" a typical MIME message.
</p>
<p>
    The decoding and encoding mechanism is designed to handle nested
    encodings, even though such messages would violate the MIME standard
    (you aren't allowed to e.g. Base64-encode a multipart/ part).  The need
    for this becomes apparent when you consider that non-MIME attachments
    (uuencoded files, forwarded messages) should be scanned as well.  For
    example, a well formed MIME message may have a Base64 encoded text/plain
    part, which itself contains a uuencoded file.  If that uuencoded file
    happens to contain a RFC822 message with multipart-MIME attachments,
    then it can be argued that the message hasn't been scanned completely
    unless the parser nests it's decoding/encoding all the way down and
    scans the contents of the uuencoded message.
</p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="hack-streams"><hr><h2>Hacking - Why treat the mail as a stream?</h2>

<p>
    The reason I'm focusing on streams of data instead of messages on disk,
    is because in my opinion streams more accurately reflect the real world
    the sanitizer must work in.  The mail system has no control over the
    length of the messages that are sent through it, so preferably resource
    usage should be influenced as little as possible by the size of those
    messages.  This is not merely a performance issue, but also one of
    security - the sanitizer is supposed to be a tool for <i>enhancing</i>
    security, so I want to ensure that installing it opens up as few new
    attack routes as possible.
</p>
<p>
    The pros of using a stream-based model:
<ul>
<li>
      Memory and disk space usage is not proportional to the size of the
      message being processed, instead it is proportional to the complexity
      of the message (MIME nesting depth etc.) and the nature of the
      security policy (third party virus scanners generally hog both memory
      and disk space). This makes the sanitizer much more scalable that it
      would be otherwise.
<li>
      Solving the basic problem of a MIME-stream decoder/encoder almost
      automatically involved solving the deeply nested encoding problem
      described above.
</ul>
</p>
<p>
    The cons:
<ul>
<li>
      There are tight constraints on what the sanitizer can do.  Once it has
      moved forward in it's input stream, it must eventually flush some of
      it's buffers and commit their contents to the output stream - and once
      it has done so, there is no turning back.  So in general, aside from
      very limited "look ahead" tests, all output must be based the
      corrosponding input data or data that came before it.  For example,
      message headers cannot be altered based on a signature at the end of
      the message body - by the time we reach the end of the message, the
      headers will have been committed to the output stream long ago.
<li>
      The constraints imposed by streaming can lead to hairy code,
      especially where two unrelated scans are forced to run simultaniously
      (e.g. in the text scanner, which must check simultaniously for
      uuencoded attachments and HTML content - two fundamentally different
      things).
<li>
      Sometimes, the stream model just doesn't work and I have to resort to
      dumping part of the message to disk anyway and working with it from
      there.  External virus scanners all (AFAIK) require this sort of
      compromise.
</ul>
</p>
<p>
Obviously, I think the benefits of streaming (scalability) are more valuable
than making my life as a programmer easier.  Besides, writing it the hard
way is much more fun!
</p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="hack-cruft"><hr><h2>Hacking - Rough edges</h2>

<p>
    There are quite a few things which need fixing and cleaning up in the
    sanitizer's code.  To name a few:
</p>
<p>
<ul>
<li>
    The sanitizer and MIMEStream are too tightly coupled - there is no well
    defined, clear interface between them.  The sanitizer's handlers
    shamelessly assume things about how MIMEStream works and mess directly
    with MIMEStream objects' internal variables.
<li>
    There's so much work to be done on standards compliance, that I've 
    devoted a <a href="#hack-standards">whole section</a> to the topic.
<li>
    The documentation needs lots of work.  Specifically, the sanitizer
    should be able to work with any MTA out there, but unless I document it
    then people won't do it.
<li>
    I really need to allow people to define policies based on MIME types or
    "magic" in addition to the current filename policies.
<li>
    The sanitizer could really use a virus-scanner front end tool which
    could do all the neat unpacking things that 
    <a href="http://www.amavis.org/">AMaViS</a> does.  It should be easy 
    enough to remove the email-related stuff from AMaViS...
</ul>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="hack-standards"><hr><h2>Hacking - Standards</h2>

<p>
    There are a relatively large number of MIME standards which the MIME
    stream editor and the sanitizer need to take into account.  In general
    security has been favored over strict compliance, especially when the
    standards mandate "ignoring" certain message parts, such as signed parts
    or message/rfc822 headers.  We sanitize those parts anyway, unless
    expressly told not to.
</p>
<p>
    Most features which are known to violate the MIME standards are optional
    and efforts will be made to make the rest of them optional as well.
</p>
<p>
    Currently, if given non MIME-compliant input, the sanitizer will
    probably generate non MIME-compliant output.  One such example is an
    illegally encoded multipart type (neither 7bit or 8bit) or an illegal
    value for the Content-Transfer-Encoding headers.  The scanner will
    accept and scan messages with some illegal encoding combinations, but
    won't correct the error.
</p>

<p><b>RFC822:</b></p>
<p>
    The sanitizer and MIMEStream module conforms to this RFC - almost.
    Currently there are probably bugs to do with header comments and
    end-of-line markers (CRLF).
</p>
<p>
    These problems will be fixed Real Soon Now.
</p>

<p>
<b>RFC2045-9</b>:  Multipurpose Internet Mail Extensions (MIME)<br>
<b>RFC2424</b>:    Content Duration MIME Header Definition<br>
<b>RFC2387</b>:    The MIME Multipart/Related Content-type
</p>
<p>
    The sanitizer appears to conform to these RFCs, as long as all scanned
    data is completely "clean" and no defanging or rewriting is necessary to
    enforce the selected policy.
</p>
<p>
    All exceptions involve possibly rewriting parts which the RFC mandates
    that MTAs treat as opaque, such as message/rfc822.  In the future a list
    of such deviations will be created, and switches added to the code to
    make such devations optional, where possible.
</p>
<p>
    Support for message/partial parts is currently incomplete, and may never
    be supported since reassembling messages is beyond the scope of this
    program and would have serious performance implications.
</p>

<p>
<b>RFC2231</b>:    MIME Parameter Value and Encoded Word Extensions.
</p>
<p>
    Partially compliant, as of 1.45.  This on my TODO list.
</p>

<p>
<b>RFC1847</b>:    Security Multiparts for MIME<br>
<b>RFC2015</b>:    MIME Security with Pretty Good Privacy (PGP)<br>
<b>RFC2480</b>:    Gateways and MIME Security Multiparts
</p>
<p>
    The sanitizer and MIMEStream module conform to these RFCs, with the
    exception of optionally sanitizing and modifying the contents of signed
    parts.  Encrypted parts probably won't be be understood by the sanitizer
    anyway, so they shouldn't be effected.  But don't be surprised if the
    sanitizer breaks PGP signatures!
</p>
<p>
    It's a matter of opinion whether I conform to RFC2480, which discusses    
    exactly these problems.  At the moment there is plenty of room for
    improvments within the sanitizer, and conformance with this RFC is one
    of my goals.
</p>

<p>
<b>RFC2311</b>:    S/MIME Version 2 Message Specification<br>
<b>RFC2312</b>:    S/MIME Version 2 Certificate Handling
</p>
<p>
    Compliant, subject to the caveats above about rewriting signed parts,
    but support is very incomplete since the contents of S/MIME messages may
    not be sanitized by the scanner since it doesn't currently recognize
    them.
</p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="feedback"><hr><h2>    Feedback </h2>

<p>
    Please let me know if you use this program!
</p>
<p>
    Without feedback I might get discouraged and start playing video games
    or work on my juggling - writing this is alot of work and at the moment
    I'm not getting paid at all to do it.  IMHO the least you can do is send
    me email...
</p>
<p>
    My email address is 
    <a href="mailto:bre@netverjar.is?Subject=Sanitizer">bre@netverjar.is</a>, 
    please put "sanitizer" somewhere in the subject line.
</p>
<p>
    Some questions:
</p>
<p><ol>
<li>
    Are you, or do you intend to use the program?  If not, why not?
<li>
    At what sort of site(s) are you using the sanitizer?
<li>
    What sort of email are you sanitizing? Incoming?  Outgoing?  Commercial?
    Private?  Mailing lists?
<li>
    Would you mind sharing your policies with other users of the program?
<li>
    What do you think is the biggest problem with the sanitizer?
<li>
    What do you think is it's best feature?
<li>
    Is the sanitizer fast enough for you?  Approximately how much mail does
    it process for you every day?  For how many users?
<li>
    Would you be willing to pay for future enhancements or support?  How
    much?  What kind of enhancements or support?  Would you be willing to
    donate money as a token of gratitude for what I've already done?
<li>
    Have you purchased any third party virus scanners, to use with the
    sanitizer?  Which one(s)?
</ol></p>
<p>
	Finally, if the program proves useful to you and you haven't time to
	contribute code, documentation or bug reports - then please consider
	<A HREF="http://orders.kagi.com/?35Q">supporting the project with
	a cash donation</A>.  I'm doing this in my spare time, and all
	encouragement helps.
</p>
<p>
    Thanks!
</p>

<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<a name="credits"><hr><h2>Credits &amp; GPL</h2>

<p>
    Copyright (C) 2000 
    <a href="http://bre.klaki.net/">Bjarni R. Einarsson</a>
    &lt;<a href="mailto:bre@netverjar.is">bre@netverjar.is</a>&gt;.<br>
    All rights reserved.
</p>
<p>
    Development of the Anomy Sanitizer, from versions 1.35 onwards, has been
    primarily sponsored by <a href="http://www.f-prot.com/">FRISK Software 
    International</a>.  Please consider buying their anti-virus products to 
    show your appreciation.
</p>
<p>
    The sanitizer contains code and implements ideas by John D. Hardin 
    &lt;<a href="mailto:jhardin@wolfenet.com">jhardin@wolfenet.com</a>&gt;.
</p>
<p>
    Kim Johnny Mathisen 
    &lt;<a href="mailto:Kim.Mathisen@haukeland.no">Kim.Mathisen@haukeland.no</a>&gt;
    contributed the instructions for 
    <a href="#in-transit-qmail">in-transit sanitizing with qmail</a>.<br>
    Mark Salazar 
    &lt;<a href="mailto:msalazar@schaferdc.com">msalazar@schaferdc.com</a>&gt;
    submitted improvements to the qmail chapter as well.<br>
    Sterling Hanenkamp 
    &lt;<a href="mailto:Sterling@nrg-inc.com">Sterling@nrg-inc.com</a>&gt;
    contributed pointers on in-transit configuration of sendmail, using the
    recommended m4 method.<br>
    
</p>
<p>
    Ideas were also borrowed from <a href="http://www.amavis.org/">AMaViS</a>
    and <a href="http://www.inflex.co.za/">Inflex</a>.
</p>
<p>
    This program is free software; you can redistribute it and/or modify it
    under the terms of the GNU General Public License as published by the
    Free Software Foundation; either version 2 of the License, or (at your
    option) any later version.
</p>
<p>
    This program is distributed in the hope that it will be useful, but
    WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    General Public License for more details.
</p>


<p>[ <a href="#top">contents</a> ]</p>
<!-- ---------------------------------------------------------------------- -->
<hr>
<p>$Id: sanitizer.html,v 1.20 2003/04/30 01:45:24 bre Exp $</p>
</body></html>
sanitizer 1.76-5 / usr / share / doc / sanitizer / sanitizer.html
