A Progress Report on Windows ASN.1 Vulnerability

By Larry Seltzer  |  Posted 2004-02-20 Print this article Print

It's too soon to tell if Windows users have dodged a bullet from Microsoft's recently-disclosed and most egregious vulnerability: ASN.1. The current assessment looks as if things could be worse.

On February 10, Microsoft disclosed a dangerous vulnerability in all modern versions of Windows, along with a patch to fix it. Nine days may not seem like a long time, but every day that goes by without a real exploit is great news. Click here for Microsofts advisory and links to the patches) At the same time, there is an exploit out in the wild that performs a distributed denial-of-service by crashing the attacked system. DDoS attacks are a bad thing, of course, but they arent as much of a worry from a mass-attack standpoint. Authors cant make a worm out of a DDoS attack because if the system crashes, theres scant opportunity to trick the owner into spreading the worm.

A real worm requires a means of infection and the ability to execute arbitrary code on the infected system. The Microsoft advisory indicates that this is possible with the ASN.1 issue.
There have been allegations that the claim of arbitrary code execution is an exaggeration, however, experts advised me that a code execution worm is merely difficult, but not impossible. Given a large number of vulnerable systems in the world, such a worm could still spread.

Heres what its all about: Without getting too specific, its not possible to write a reliable exploit that gains control of the target system. According to Ken Dunham, director of malicious code at iDEFENSE, "The heap overflow exploit is proving to be more difficult for some attackers than what they had originally thought. A change of state makes it more difficult to successfully exploit computers." In other words, the attack requires conditions on the PC which cannot be predicted or controlled by the attacker.

But even if, for the sake of argument, only 1 percent of attacks succeed, that would encompass enough computers for the worm to spread far, assuming it wont do serious damage to systems that it cant successfully infect. The worm will keep trying and trying and eventually, it will get through— if there are enough unpatched systems for it to find. Meanwhile, if unsuccessful attacks crash the system or do something else to tip the owner off of the worms presence, the jig will soon be up.

Next Page: What About Windows 98?

Larry Seltzer has been writing software for and English about computers ever since—,much to his own amazement—,he graduated from the University of Pennsylvania in 1983.

He was one of the authors of NPL and NPL-R, fourth-generation languages for microcomputers by the now-defunct DeskTop Software Corporation. (Larry is sad to find absolutely no hits on any of these +products on Google.) His work at Desktop Software included programming the UCSD p-System, a virtual machine-based operating system with portable binaries that pre-dated Java by more than 10 years.

For several years, he wrote corporate software for Mathematica Policy Research (they're still in business!) and Chase Econometrics (not so lucky) before being forcibly thrown into the consulting market. He bummed around the Philadelphia consulting and contract-programming scenes for a year or two before taking a job at NSTL (National Software Testing Labs) developing product tests and managing contract testing for the computer industry, governments and publication.

In 1991 Larry moved to Massachusetts to become Technical Director of PC Week Labs (now eWeek Labs). He moved within Ziff Davis to New York in 1994 to run testing at Windows Sources. In 1995, he became Technical Director for Internet product testing at PC Magazine and stayed there till 1998.

Since then, he has been writing for numerous other publications, including Fortune Small Business, Windows 2000 Magazine (now Windows and .NET Magazine), ZDNet and Sam Whitmore's Media Survey.

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