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pask	I'm proud to introduce Mr. Jose Nazario from Monkey.org (USA)
pask	Dr. Nazario holds a Ph.D. in biochemistry from Case Western Reserve University but currently works as a system
pask	verification and security analyst for an American networking company. He has been active in the Open Source software and
pask	security community for several years.
pask	The conference's title is Vthrottle: stopping mail viruses through libmilter
pask	the audience could download some slides
pask	from jose's web at monkey.org, exactly at http://monkey.org/~jose/software/vthrottle/
pask	The conference will be translated simultaneously to spanish at #redes channel and to dutch at #taee channel. The attendants could ask, just at the end of conference , at #qc channel
pask	The #linux channel would remain moderated til the end of conference.
pask	Ok,
pask	and now,
pask	jose,
pask	the channel is waiting for you!!
jose_n	good afternoon/day/night/morning ... my name is jose nazario.
jose_n	thank you pask for that great introduction. i'm
jose_n	an openbsd developer and security analyst living in ann arbor,
jose_n	michigan, in the united states.
jose_n	i'm going to be presenting today on
jose_n	some software i wrote recently called 'vthrottle'.
jose_n	as pask said, the slides for the talk are on my website here:
jose_n	http://monkey.org/~jose/presentations/vthrottle.d/
jose_n	the concept behind vthrottle is not mine, it belongs to an HP
jose_n	labs researcher named matt williamson.
jose_n	he and his research
jose_n	group have been investigating using activity rate limiting
jose_n	mechanisms to prevent network anomalies from growing too
jose_n	quickly.
jose_n	i became aware of this research while writing a book
jose_n	on internet worms which was published last month.
jose_n	in a nutshell the technique seems to have some promise to it,
jose_n	but i'm not entirely convinced it will work for everything.
jose_n	so, i decided to write up and release some software to test it to
jose_n	see how well it will work in the real world.
jose_n	this software is
jose_n	only at version 0.30, but it is very stable and has most of the
jose_n	features it will need for a 1.0 release.
jose_n	[slide 2]
jose_n	so, very quickly, vthrottle is a mail server plugin that allows
jose_n	you to modify server behavior.
jose_n	it operates at the MTA layer, or mail transport agent.
jose_n	this is where the SMTP transaction occurs
jose_n	between servers and clients.
jose_n	this is different than your mail
jose_n	client, which is called an MUA (mail user agent) or the software
jose_n	which drops the mail off into your inbox, which is called the
jose_n	LDA (local delivery agent).
jose_n	vthrottle doesn't stop worms, it only slows them down.
jose_n	you'll never win the race ahead of a worm, so what you want to do is
jose_n	to try and gain some extra time to react.
jose_n	to do this, and to do
jose_n	this for worms we haven't seen yet, we work on generic worm
jose_n	properties.
jose_n	we never look at the payload, we only look at the
jose_n	behavior of a host.
jose_n	the implementation is built as a milter plugin for sendmail
jose_n	severs.
jose_n	milter is the plugin architecture for sendmail, which
jose_n	lets you interact with the server and make judgements about mail.
jose_n	[slide 3]
jose_n	let's take a few minutes and talk about libmilter.
jose_n	libmilter is
jose_n	the sendmail plugin architecture, as i said on the last slide.
jose_n	it is a library for the client code, and the server needs support
jose_n	for it as well at compile time.
jose_n	it is for sendmail only, not
jose_n	for postfix, qmail, exim or the like.
jose_n	it provides a framework for interacting with mail by working on
jose_n	state transitions within smtp.
jose_n	these transitions occur when
jose_n	a client connets, it says HELO, it sets the "mail from",
jose_n	who
jose_n	the mail is going to, and when it sends the headers, when
jose_n	the headers end, when it sends the body of the mail,
jose_n	and when the
jose_n	body of the mail ends, when the message ends, and when the
jose_n	client aborts the connection.
jose_n	milter clients listen on a local domain (UNIX) socket or a
jose_n	network (IPv4 or IPv6) socket.
jose_n	this lets your run a single milter
jose_n	server for all of your MTA farm and work with multiple SMTP
jose_n	servers.
jose_n	[slide 4]
jose_n	people have typically been using milter plugins for the following
jose_n	four reasons.
jose_n	the first is as a mail logger mechanism. this lets your copy all
jose_n	of a subset of the messages that pass through a system, for
jose_n	example for archiving or record keeping purposes.
jose_n	the second is to use it as a statistics gatherer.
jose_n	this can
jose_n	be things like a mail quota information gatherer, a connection
jose_n	counter, or the like. i'm looking at using this information
jose_n	to further a generic worm detection and control mechanism.
jose_n	the third is as an antivirus subsystem hook.
jose_n	you can feed
jose_n	the antivirus software the mail message itself and return information
jose_n	about the message to the server.
jose_n	oops .. duplicate :)
jose_n	here you can do things like
jose_n	reject or pass a mail message after inspection.
jose_n	the fourth one is as an anti-spam mechanism. similar to the
jose_n	antivirus mechanism, you can pass the message or header information
jose_n	to the anti-spam subsystem and pass or fail messages this way.
jose_n	as i alluded to in the previous slides, milter can actually
jose_n	*do* things to your mail connections.
jose_n	you can react to a
jose_n	state transition request by giving a pass code (a 200 series
jose_n	reply), or a failure (400 for a temporary failure or 500 for
jose_n	a permanent failure).
jose_n	coming 8.13 you can quarantine messages
jose_n	using libmilter.
jose_n	you can also modify the mail as it passes through the system.
jose_n	here what you can do is add headers (such as "X-SPAM"), or
jose_n	even rewrite portions of the message (such as defanging an
jose_n	attachment, modifying a message body or the like).
jose_n	lastly you can copy messages silently using the milter system.
jose_n	this can basically open up a file and dump the message body
jose_n	into the file, including the headers and the body of the message.
jose_n	[slide 6]
jose_n	using libmilter is very easy to do.
jose_n	the first step is to build
jose_n	a sendmail program that has libmilter support added in already.
jose_n	the first step is to build
jose_n	a sendmail program that has libmilter support added in already.
jose_n	oops
jose_n	our network broke for a bit
jose_n	using libmilter is very easy to do. the first step is to build
jose_n	a sendmail program that has libmilter support added in already.
jose_n	then you basically add a milter call in the configuration,
jose_n	forcing messages to pass the check called by the milter program.
jose_n	the next thing to do is to write the milter program. what you
jose_n	do is you fill in a struct which tells the program what functions
jose_n	to call at what points for these state transitions within an
jose_n	SMTP transaction.
jose_n	and, of course, you can set them to NULL
jose_n	if you wish them to not be evaluated. these are just function
jose_n	pointers.
jose_n	next you write the functions which evaluate the portion of the
jose_n	SMTP transaction.
jose_n	all functions can treate the body as a
jose_n	string, but you have to be careful about embedded NULLs. all
jose_n	methods return one of pass, fail, or reject.
jose_n	within the program you need to connect to the socket you have
jose_n	set up to communicate with the MTA program (a UNIX domain
jose_n	socket or a network socket).
jose_n	then the last thing you need to
jose_n	do is call smfi_main(), which starts the milter program.
jose_n	someone asked in #qc if milter like tools exist for qmail. nope, not that i know of.
jose_n	i dont use qmail, but i'm pretty sure milter wont work with qmail and support for milter like tools don't exist.
jose_n	[slide 7]
jose_n	milter programs are typically written in C or C++, but bindings
jose_n	have been written in Perl. perl milters have the same basic
jose_n	structure as a C milter does.
jose_n	it should be easy to write milter bindings for other languages
jose_n	using the SWIG toolkit.
jose_n	then you could write in Python, Ruby,
jose_n	tcl, C# or whatever else you like that SWIG supports. i don't
jose_n	think anyone has done this yet.
jose_n	[slide 8]
jose_n	vthrottle works very very simply. it has three parts of the SMTP
jose_n	transaction it watches.
jose_n	the first is who connects to the
jose_n	mail server. the second is how you say HELO (how you start the
jose_n	SMTP transaction). and the third is the address the mail is
jose_n	coming from.
jose_n	for the connection and HELO information the
jose_n	hostname is kept and compared; for the "mail from" segment
jose_n	an email address is used.
jose_n	for each of these pieces of information, vthrottle keeps a list
jose_n	of who it has seen and when they were seen.
jose_n	what vthrottle
jose_n	then does is it looks at the current time and the list time it
jose_n	saw any of those obervations and enforces a minimum interval
jose_n	between those observations.
jose_n	we make two pretty bold assumptions here, first that normal hosts wont
jose_n	try and send mail faster than this limit.
jose_n	and the second part
jose_n	of this assumption is that we figure most worms and viruses
jose_n	will try and send mail faster than this limit.
jose_n	like i said earlier, this isn't my idea, it's from matt williamson.
jose_n	he's a researcher in the UK working for HP labs.
jose_n	[slide 9]
jose_n	vthrottle is very easy to install.
jose_n	first make sure that your
jose_n	sendmail has support for milter build it and that you have the
jose_n	milter library and headers installed.
jose_n	this is part of the
jose_n	normal sendmail distribution, so you dont need any special
jose_n	software.
jose_n	then, obviously, download the software from my site:
jose_n	http://monkey.org/~jose/software/vthrottle/
jose_n	the current version is 0.30, which i released last weekend
jose_n	(14 december 2003).
jose_n	building vthrottle can be a bit tricky, only because i dont
jose_n	have a ./configure script yet.
jose_n	you need to modify the Makefile
jose_n	to point it at the libmilter headers and the library.
jose_n	then you can install it wherever you like. the README lists the
jose_n	configuration change you need to make to your sendmail.mc file.
jose_n	once you regenerate your .cf file you're all set.
jose_n	you start it very simply: vthrottle -s <socket>, which is
jose_n	the communications socket for the program.
jose_n	you can
jose_n	set a different interval time with -i (it defaults to 60 seconds right now).
jose_n	you can create a "whitelist" using
jose_n	-w, too. this file specifies different limits for mail addresses
jose_n	or hosts.
jose_n	[slide 10]
jose_n	these are the big features of vthrottle right now, over its
jose_n	basic behavior.
jose_n	you can configure a default interval that
jose_n	works for your network or your behavior.
jose_n	let's say people in
jose_n	your office send mail every 30 seconds on average, you can
jose_n	change the behavior on the command line at runtime.
jose_n	you can also whitelist hosts or mail addresses using the
jose_n	whitelist function.
jose_n	this is for major peer MTA systems or
jose_n	mailing list addresses. you can set a different interval
jose_n	for those entries.
jose_n	[slide 11]
jose_n	this is a basic order of operations for a mail server using
jose_n	vthrottle.
jose_n	when a host connects or says HELO, vthrottle looks at its
jose_n	list of hosts and when they were seen.
jose_n	if it has seen the
jose_n	host before, it compares the time now to when it was last
jose_n	seen and how long you are supposed to wait.
jose_n	if it's longer
jose_n	than the required interval, then vthrottle says "ok" and
jose_n	the message is allowed.
jose_n	f it hasn't seen the host
jose_n	before, it adds it to the list and moves on with an "ok".
jose_n	if the connection is too soon, vthrottle tells the server
jose_n	to reject the transaction.
jose_n	when the source mail address is sent, vthrottle repeats that
jose_n	check on a list of mail addresses.
jose_n	if they are at least
jose_n	"interval" seconds apart, then the mail can pass. if not
jose_n	the message attempt fails.
jose_n	whenever an attempt to send mail is prevented by a rejection
jose_n	or a failure, it is logged for the administrator.
jose_n	[slide 12]
jose_n	vthrottle has some bugs ... some of which are my fault.
jose_n	the first is that it sends a permanent failure to the
jose_n	host when it tells it to go away for a connection or a
jose_n	HELO request.
jose_n	this is specified by the SMTP standards and
jose_n	is limited by sendmail.
jose_n	the second is that the list used in vthrottle is global.
jose_n	because vthrottle is threaded, it will probably destroy
jose_n	the list and make it useless ...
jose_n	the third bug is more of a performance problem i expect to
jose_n	see. it uses a singly linked list to look up addresses,
jose_n	so performance will degrade with the number of addresses
jose_n	and hosts your servers interact with.
jose_n	maybe i should use
jose_n	a splay tree, which is self optimizing ...
jose_n	[slide 13]
jose_n	this is a short list of things i plan to do with vthrottle
jose_n	for a 1.0 release.
jose_n	the first is to fix sendmail with a
jose_n	patch to get it to return a temporary failure for a
jose_n	connection or HELO throttle action.
jose_n	this should make
jose_n	clients react more sanely and try again in a few minutes.
jose_n	the next two i already did. you should be able to vary the
jose_n	default interval, which you can now do. the third is to
jose_n	improve the whitelist file syntax, and that is done, too.
jose_n	lastly i need to implement a deferment queue for messages
jose_n	that have been throttled. this will be trickier but will
jose_n	make the server easier to manage large queues of
jose_n	mail rather than hoping the client gets it right.
jose_n	[slide 14]
jose_n	sadly, i don't run mail servers anymore. so, i haven't
jose_n	tested vthrottle in the real world. for all i know it's
jose_n	dead slow and ruins your mail server.
jose_n	it could be, because
jose_n	it has to traverse this linked list of information, but that
jose_n	depends on the network size.
jose_n	obviously i hope vthrottle doesn't have a negative impact on
jose_n	normal network operations.
jose_n	the worst case scenario for
jose_n	this kind of impact is that someone will be away from the
jose_n	network for a while and compose a bunch of mail. when they
jose_n	sit down to send it out, that "shotgun" blast of mail
jose_n	will be throttled. a deferment queue will help a lot in that
jose_n	regard.
jose_n	[slide 15]
jose_n	there are some weaknesses in the design which i want to see if
jose_n	i can work around.
jose_n	the first is when a host reuses its existing connection via an
jose_n	SMTP RSET (reset state). what i should do here is start the
jose_n	check again and pretend it connected again. should be simple
jose_n	to do if libmilter has a handler for RSET ...
jose_n	the second is the situation when the virus spoofs the HELO
jose_n	information. remember you can send anything you want here,
jose_n	and the server doesn't have to verify it. i imagine some
jose_n	viruses already do this.
jose_n	the mail. in the absence of strong authentication (ie via
jose_n	TLS) of the sender, there is no way around this one.
jose_n	[slide 16]
jose_n	and that's it! i need to thank matt williamson and the
jose_n	management team at HP labs, they were comfortable
jose_n	enough with someone else releasing a product which
jose_n	does what their patent pending process does. :)
jose_n	you can see the latest release of vthrottle on its homepage:
jose_n	http://monkey.org/~jose/softwaree/vthrottle/
jose_n	the website needs sexy graphics if you feel like contributing.
jose_n	i have some ideas but i'm not a good artist.
jose_n	lastly this took only a few hours to write and extend,
jose_n	but getting it up to version 0.30 took about 400 lines of C
jose_n	code and about 6 hours of work.
jose_n	thank you :)
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