Over at the Matasano Blog :)

Matasano 's Blog quoted my post on Office bugs, and Ivan Arce made some excellent points in the comments:

1. 'They are inherently one-shot. You send a bad file, and while the user might try to open it multiple times, there is no way the attacker can try different values for anything in order to get control.”'

IA: OK. good point but…think about scale & diversity. Even in a targeted attack sending a one-shot client-side exploit against N desktop systems will with one hardcoded address will offset the value of ALSR with some probability of success for a given N. The attacker only needs ONE exploit instance to work in order to break into ONE desktop system, after that it is game over. Client-side bugs are one shot against the same system but not necesarrilly so against several systems in parallel.

Very true, I did overlook this. It also explains the use of really low-value phone-home bots as payload: If you're going to attack in such a "wide" manner, you essentially accept detection as long as you can compromise one of the relevant clients. This means that whatever you are sending will be lost, and therefore you won't send anything more sophisticated than a simple bot.

” 2. There can not be much pre-attack reconnaissance. Fingerprinting server versions is usually not terribly difficult (if time consuming), and usually one can narrow down the exact version (and most of the times the patch level) of a target before actually shooting valuable 0day down the wire. With client side bugs, it is a lot more difficult to know the exact version of a piece of software running on the other side - one probably has to get access to at least one document created by the target to get any data at all, and even this will usually be a rough guesstimate.”

IA: Hmmm not sure about this either. I would argue the desktop systems (clients) leak A LOT more information about themselves than servers and, generally, those leaks are much less controlled and/or controllable and easier to elicit than server leaks. After all, as a general principle, client apps are _designed_ to provide information about themselves.

Not to mention that a lot of information about your desktop systems has *already* leaked and is publicly available on the net now (server logs, emails, documents, stray packets, etc.), you just need to know how and where to look for it.

I disagree on this to an extent. My system leaks information about my mail client because I participate in public forums etc, but the majority of corporate users never gain any visibility outside of the internal network. Most people just don't use mailing lists or usenet etc. So it will be comparatively easy to attack some security officer (hey, I know his exact client version), but the CEO's secretary (which might be a lot more interesting as a target, and less likely to notice her computer is compromised) will be more or less "invisible".

Unbelievable but true

I am decompressing a bit after a few weeks of insane stress and thus I am actually reading blogs. And to my greatest surprise, I ended up reading this one. Now, Oracle security has never interested me ever since I tried to audit it in 2000 and it kept falling over without a fight (or without us really doing anything except sending a few letters to it), but I have to admit that Ms. Davidsons blog has a pretty high entertainment value (at least for me, a morallically degenerate piece of eurotrash full of the afterglow of a once good education system), AND it is refreshing to see someone with a bit of a classical education in IT security (I get picked upon regularly for the fact that I got my Latinum "on the cheap" and know jack shit about old greek - then again, my circle of friends includes a mathematician that claims that he can, by means of listening to a record, tell you in which church in france a certain piece of organ music was played, and hence I am always the loud and stupid one).

Anyhow, given Oracle's horrible code quality, I am very much positively surprised at the quality of Ms. Davidsons blog. And given what most people that have worked with static analysis tools before would describe as a horrible mistake in evaluating tool quality, I would like to mention that mathematics and geometry are part of a classical education. Whoever decided on the right source code analysis tool to use for detecting flaws in Oracle apparently failed that part.

Client Side Exploits, a lot of Office bugs and Vista

I have ranted before about careless use of 0day by seemingly chinese attackers, and I think I have finally understood why someone would use good and nice bugs in such a careless manner:

The bugs are going to expire soon. Or to continue using Dave Aitel's and my terminology: The fish are starting to smell.

ASLR is entering the mainstream with Vista, and while it won't stop any moderately-skilled-but-determined attacker from compromising a server, it will make client side exploits of MSOffice file format parsing bugs a lot harder.

Client-side bugs suffer from a range of difficulties:

1. They are inherently one-shot. You send a bad file, and while the user might try to open it multiple times, there is no way the attacker can try different values for anything in order to get control.
   
2. There can not be much pre-attack reconnaissance. Fingerprinting server versions is usually not terribly difficult (if time consuming), and usually one can narrow down the exact version (and most of the times the patch level) of a target before actually shooting valuable 0day down the wire. With client side bugs, it is a lot more difficult to know the exact version of a piece of software running on the other side - one probably has to get access to at least one document created by the target to get any data at all, and even this will usually be a rough guesstimate.
   

As a result of this, client-side bugs in MSOffice are approaching their expiration date. Not quickly, as most customers will not switch to Vista immediately, but they are showing the first brown spots, and will at some point start to smell.

So you're in a situation where you're sitting on heaps of 0day in MSOffice, which, contrary to Vista, was not the biggest (private sector) pentest ever (This sentence contains two inside jokes, and I hope that those who understand them aren't mad at me :-). What do you do with those that are going to be useless under ASLR ? Well, damn, just fire them somewhere, with some really silly phone-home-bots inside. If they bring back information, fine, if not, you have not actually lost much. The phone-home bots are cheap to develop (in contrast to a decent rootkit) and look amateurish enough as to not provoke your ambassador being yelled at.

If you are really lucky, you might actually get your opponent to devote time and resources to countermeasures against MS Office bugs, in the hope they don't realize that work will be taken care of elsewhere. In the meantime, you hone your skills in defeating ASLR through out-of-defined-memory-read-bugs (see some blog post in the next few days).

On a side note, I am terribly happy today. I've had more luck this week than I deserve.

While we're all talking about the next overflow and think that they have significance in the wider scheme of things, I'll climb on the soapbox for 5 minutes:

We should send peacekeeping troops to Darfour/Sudan. I was strongly opposed to the Iraq war (on the ground that invasion would bring civil war), but I plead my government: Take my taxes and send peacekeeping forces to Sudan. _If_ we have decided that the 'europeans-are-from-venus'-stance is obsolete, we have here a primary example of a conflict where external invasion appears necessary according to almost everybody (except the government in Kartoum).