Just recently, Dell SecureWorks Counter Threat Unit(TM) (CTU) researchers published details (see http://www.secureworks.com/cyber-threat-intelligence/threats/skeleton-key-malware-analysis/ ) on a especially nasty piece of malware that bypasses authentication on Active Directory (AD) systems which implement single-factor (password only) authentication. Once deployed the malware stays quite noiseless in the Domain Controller´s (DC) RAM, and the DC´s replication issues caused by it weren´t interpreted – in this case – during months as a hint for system compromise. Probably the malware´s modification on the LSASS process reduced the DC´s ability to perform DC-to-DC authentication, but this is only speculation and not where we would like to go today.
So, what to do? The relevant mitigations, pointed out by Dell´s CTU, as event log monitoring and scanning processes on suspicious systems with the published YARA signature should be applied.
Still, let’s discuss for a second which long-term, preventative measures could come into play as well. Continue reading “Skeleton Key – a Nasty Piece of Malware. Some Remarks.”
A few days ago the European Network and Information Security Agency (ENISA) published this quite interesting document with the exact title. Here’s what it covers:
“The booming smartphone industry has a special way of delivering software to end-users: appstores. Popular appstores have hundreds of thousands of apps for anything from online banking to mosquito repellent, and the most popular stores (Apple Appstore, Google Android market) claim billions of app downloads. But appstores have not escaped the attention of cyber attackers. Over the course of 2011 numerous malicious apps were found, across a variety of smartphone models. Using malicious apps, attackers can easily tap into the vast amount of private data processed on smartphones such as confidential business emails, location data, phone calls, SMS messages and so on. Starting from a threat model for appstores, this paper identifies five lines of defence that must be in place to address malware in appstores: app review, reputation, kill-switches, device security and jails.”
Just read through it and while I’ve never been a big fan of STRIDE (mainly due the application centric approach which simply is not my cup of tea) I have to say it’s applied elegantly to the “app ecosystem” described in the paper.
The doc somewhat accompanies this one titled “Smartphones: Information security risks, opportunities and recommendations for users” (released by ENISA in late 2010), which is a valuable resource in itself.
Overall excellent work from those guys in Heraklion, providing good insight from and for practitioners in the field.
Recently I noticed this news titled “New email worm on the move”. At roughly the same time I received an email from a senior security responsible from a large customer asking for mitigation advice as they got “hit pretty hard” (by this exact piece of malware).
Given I’m mainly an infrastructure and architecture guy usually I’m not too involved in malware protection stuff (besides my continuous ranting that – from an architectural point of view – endpoint based antivirus has a bad security benefit vs. capex/opex ratio). So I’m by no means an expert in this field. Still I keep scratching my head when I read the associated announcements (like this, this or this) from major “antivirus”, “malware protection” or “endpoint security” vendors – to save typing, in the remainder of the post I call them SNAKE vendors (where “SNAKE” stands for “Smart Nimble APT Kombat Execution”… or sth equally ingenious of the valued reader’s choice… 😉
The following (not too) heretical questions come to mind:
a) What’s the corporate need to allow downloading .scr files at all? Maybe I’m missing sth here or I’m just not creative enough but I (still) don’t get it. Why not block .scr at the network boundaries at all?
[yes, I know, there’s no such thing like “well-defined network boundaries” any more, but here we’re talking about “HTTP based downloads” which happen to pass through – a few – centralized points in quite some environments].
a1) So, maybe blocking downloads of .scr files (as this document recommends, funnily enough together with the recommendation to “filter the URL” on gateways… which really seems an operationally feasible thing for complex environments… and a very effective one, for future malware, too ;-)) might be a viable mitigation path.
In my naïve world the approach of just allowing a certain (“positive”) set of file/MIME types for download would be even better, wouldn’t it?
This reminds me of a consulting project we did for a mid-sized bank (20K users) some years ago. They brought us in to evaluate options to increase their “malware protection stance” and we finally recommended a set of policy and gateway configuration adjustments (instead of buying a third commercial antimalware software which they had initially planned). Part of our recommendations was to restrict the file types to be accepted as email attachments. For a certain file type (from the MS Office family and known as a common malware spread vector at the time) they strongly resisted, stating “We need to allow this, our customers regularly send us documents of this type”. We then suggested monitoring the use of various filetypes-in-question for some time and it turned out that for this specific type they received three (in numbers: 3) legitimate emails within a six month period…
b) In their mentioned announcements all major vendors boast disposing of “updated signatures providing total protection” for this piece of malware.
Hmm… again, very naïvely, I might ask: so why did our customer get “hit pretty hard” (and, following the press, other organizations as well)? They are not a small shop (actually they’re one of the 50 largest corporations in the world), there’s a lot of smart people working in the infosec space over there and – of course! – they run one of the main “best of breed” antimalware solutions on their desktops.
So why did they get hit? I leave the answer to the reader… just a hint: operational aspects might play a role, as always.
“Upon further investigation, we found that the malware used for this attack was just an unpacked version of a file that we already detected as WORM_AUTORUN.NAD. It is possible that the cybercriminals behind this attack got hold of the code for WORM_AUTORUN.NAD and modified it for their usage.”
Indeed, looking at this entry in Microsoft’s malware encyclopedia from august 19th there are remarkable similarities.
So, dear SNAKE vendors: do I get it correctly that (most of) you need a new signature when there’s an unpacked version of some malicious piece of code, as opposed to a packed version (of the same code)?
Seems quite a difficult exercise for all those super-smart heuristic adaptive engines … in 2010…
Sorry, guys, how crazy is this? And it seems the stuff was initially observed back in july.
[did you note that they don’t even feel embarrased by admitting this, but proudly display this as a result of their research, which of course takes place in the best interest of their valued customers?]
For completeness’ sake it should be mentioned that this piece of malware (no, I won’t rant on the fact that – still, in 2010 – it seems not possible to have a common naming scheme amongst vendors) performs, amongst others, the following actions on an infected machine:
– turning of security services.
– modification of some security-relevant registry keys.
– sharing system folders.
On most Windows systems all those actions can only be performed by users… with administrative privileges…
Overall, this “classic piece of worm” might remind us, that maybe effective desktop protection should be achieved by
– controlling/restricting which types of code and data to bring into a given environment.
– or, at least, _where_ to get executable (types of) code/data from.
– which executables to run on a corporate machine at all (yes, I’m talking about application whitelisting here ;-).
– reflecting on the need of administrative privileges.
and _not_ by still spending even more money for SNAKE oil.
I renew my plea from this post:
So, please please please, just take a small amount (e.g. 1%) of the yearly budget you spend on antimalware software/support/operational cost, get a student intern in and have her start testing application whitelisting on some typical corporate desktops. This might contribute to a bit more sustainable security in your environment, one day in the future.