Delivering the 12kb Bomb

[InfoSec News <isn () c4i org>]

http://www.theregister.co.uk/content/55/36345.html

By Kelly Martin
SecurityFocus
Posted: 17/03/2004

The average size of email-bourne viruses so far this year has been 
well under 20 kilobytes. A young virus writer, sitting in his 
underwear in his parent's dark basement, takes a hex editor and 
modifies a few bytes of the latest Netsky.M (16.5kb), Beagle.J (12kb) 
or Mydoom.G (20kb) mutation, spawns a new virus variant, and then 
releases it into the wild. The resulting few thousand compromised 
machines, a conservative estimate perhaps, will sit naked as drones or 
"bots" on the Internet, waiting patiently for their summons and 
commands. 

A mere 12 kilobytes of action-packed code is impressive. For a 12 
kilobyte Beagle, you get total system compromise, plus a highly 
effective spam engine. This short column, in comparison, is about 29kb 
of plain text and HTML. A 12 kilobyte binary is thus very small. The 
latest code that brings a Microsoft computer to its knees is small 
enough that it could be silk-screened onto an extra-large t-shirt: a 
walking time bomb, if you will. With today's monolithic software 
programs and operating systems, often barely fitting compressed on a 
CD-ROM, it's easy to see how small bits of malicious code can slip 
under the radar. 


David vs. Goliath 

I still remember the days, many computer-years ago now, when 
BackOrifice and SubSeven Trojans first came out. At just over 100kb, 
they were impressive in their day. Back then most people were running 
Windows 98, and a small 100kb email attachment could easily slip into 
the operating system and wreak havoc without ever being noticed. Today 
these are 100kb Trojans are monolithic in comparison to our modern 
email-based worm-virus-backdoor-spam-engines that tend to be under 
20kb; these old relics are still a useful footnote, however, for 
watching the long-term evolution of malicious code. 

Speaking of monolithic: Windows XP Home Edition requires approximately 
1,572,864 kilobytes (1.5Gbytes) for a typical install, according to 
Microsoft. Of course, it's better/faster/easier-to-use than previous 
versions, as the advertisements say, and if you believe the literature 
too it's also less buggy and significantly more secure. The public 
relations spin machine for such a large company is fascinating to me - 
Windows has become bloated into millions and millions of lines code, 
yet it only takes a mere 12 kilobytes to provide full system 
compromise and an annoying spam engine. The divide between David and 
Goliath has never been greater. 

Consider an analogy on the size of modern malicious code: if Windows 
XP were the size of the Empire State Building, then the little barking 
Beagle virus - the size of a small dog - can come in through the front 
door, lift its leg, deliver its payload, and somehow cause the entire 
building to come crumbling down. Or, Beagle can simply hold the door 
open automatically, so that a large cement truck can drive in and 
deliver its mystery payload to the base of the operating system as 
required. 


When Size Matters 

The latest craze in the virus-worm-spam war has seen computer worms 
crawling inside of other computer worms - like watching maggots crawl 
on top of each other as they make their way through a tender piece of 
meat. Some of the latest worms found in the wild have multi-vector 
propagation algorithms and also make use of previous viral infections 
by Beagle and Mydoom. So basically you start with 12kb of code, 
whereby Beagle slips into your email and under the radar, opens a 
backdoor, and then gets automatically disabled and replaced later in 
the week by a yet-more malicious and larger piece of worm code - 
perhaps new code that tunnels the user's GUI onto the Internet, 
provides full remote-control capabilities, records keystrokes and 
searches for a user's sensitive data. 

Worms are crawling on top of worms, eating out holes in Microsoft's 
dominant operating systems like a giant piece of swiss cheese in front 
of thousands of tiny, malicious rats. I do not know to what extent 
Microsoft's code is scrutinized through an exhaustive security audit, 
but two years after Bill Gates' long-heralded announcement the holes 
in the cheese are larger than they've ever been. 

It is no wonder that dozens of virus variants appear just a week or 
two after the first incarnation is released into the wild - fitting a 
backdoor and a highly effective SMTP spam engine into a mere twelve 
kilobytes of code is not easy, and many young programmers want to 
learn how it's done. Microsoft could learn a few things from these 
bright, if mis-aligned, people to help them write more efficient code. 

Perhaps with more efficient code, Windows XP on a modern AMD Athlon, 
Intel Pentium or Celeron with a gig of RAM would actually run more 
quickly and be more secure than Windows NT was on an old P-100 with 32 
Mb of RAM. Who knows? For now we're stuck with millions and millions 
of lines code compiled into a giant operating system that can be wiped 
out of existence remotely with nothing but a small 12 kilobyte piece 
of code, launched by someone in his underwear on the other side of the 
world. 



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