RE: Randomly obfuscated JavaScript code beats AV scanners

["Debasis Mohanty" <debasis.mohanty.listmails () gmail com>]

Funny that this made news! 

Obfuscating malicious javascript code to evade AVs is so 5+ yrs old. The
only thing I believe new in this news is the way it obfuscates the code
every time the page is loaded. However the fact that is obfuscated in this
whole crappy news is, this kind of mal code obfuscation can only evade AVs
which are actually incapable (NOD32, AVG etc) of doing behavioural/heuristic
analysis. Any decent AV like Symantec, F-Secure or McAfee will be able to
block such codes irrespective of the way the malware obfuscate the code.
Most of the current AVs with behavioural analysis will trap malicious
command executions by javascript by monitoring libraries like wsscript or
kernel level hooks. No decent AVs will behave immaturely by detecting
javascript malicious code by only using signatures. 

-d

________________________________________
From: funsec-bounces () linuxbox org [mailto:funsec-bounces () linuxbox org] On
Behalf Of 'Richard M. Smith'
Sent: 04 August 2007 01:57
To: funsec () linuxbox org
Subject: [funsec] Randomly obfuscated JavaScript code beats AV scanners

http://www.infoworld.com/article/07/08/03/Malignant-Javascript-mutates_1.htm
l 
SANS' Internet Storm Center (ISC) said on Thursday it has come across the
attack on a compromised Web site, where an iframe was used to deploy various
pieces of malicious code via JavaScript; iframes allow content from one Web
site to be embedded in another Web site. 
This technique itself isn't new, but researchers found that the server
deploying the malicious JavaScript was heavily modifying it -- "obfuscating"
it -- so as to be undetectable by anti-virus detectors, the ISC said.
Moreover, the obfuscations were generated randomly and on the fly, according
to ISC handler Bojan Zdrnja. 
"What makes this new is that the hosting Web site generates this code
dynamically," he wrote in an analysis. "Every time you request this Web
page, it will use completely random names for all variables and functions
... changing variable and function names even causes the payload information
to change." 
The technique makes the script code effectively undetectable by common types
of malware scanners, Zdrnja said.



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