[WEB SECURITY] JavaScript Obfuscators

Eric Rachner eric at rachner.us
Sun Jan 25 05:12:34 EST 2009


The short answer is that no obfuscator can be so powerful as to really
confuse the Javascript parser of any browser with which it is intended to be
compatible.

 

At the end of the day, a (de)obfuscator must present code to the browser au
natural, or it won't run.  Personally, I won't spend time writing utilities
to attack individual obfuscators because I know that every obfuscator must
eventually stop pretending to be clever and pass a blob of plaintext
javascript to the host browser for interpretation.  If I want to know what's
going on, I can just hook/inspect whatever is given the browser.

 

In my opinion, the only real reason to care about the behavior of a given
obfuscator is academic: sometime's it's interesting to guess at whatever the
malware author might be thinking.

 

- Eric

 

From: Sophia Sun [mailto:sophiasfq at gmail.com] 
Sent: Saturday, January 24, 2009 8:09 PM
To: James Landis
Cc: websecurity at webappsec.org
Subject: Re: [WEB SECURITY] JavaScript Obfuscators

 

Thanks for pointing out the ambiguity, James.

I'm interested in examining how obfuscated a piece of JavaScript code can
be. Both commercial and open-source obfuscators for JavaScript only (static
JavaScript "compiler") are of interest to me. I would like to know what
kinds of obfuscation techniques are being used in an obfuscator, such as the
randomization of variable names and function names and code shuffling.

I agree with you that client-side code manipulation provides no real
security value. But think about obfuscation from a web administer's
standpoint, a highly obfuscated piece of JavaScript code could possibly
delay the detection of a payload. Take XSS worms for example, it seems to me
that most of them are obfuscated. It would be nice to know what obfuscation
techniques are commonly used in obfuscators and how powerful an obfuscator
can be in obfuscating JavaScript code.

--Sophia

On Sat, Jan 24, 2009 at 6:10 PM, James Landis <elspood at gmail.com> wrote:

More parameters please. Commercial or open-source? Do you want the
obfuscated output or the obfuscator itself? JavaScript only or
JavaScript + HTML? Dynamic server-side runtime obfuscators or static
JavaScript "compilers"?

As I'm sure you know this, given the fact that you explicitly use the
word "obfuscator", but manipulation of client-side code provides no
real security value beyond prevention of casual theft and reuse of
code.

-j


On Sat, Jan 24, 2009 at 4:53 PM, Sophia Sun <sophiasfq at gmail.com> wrote:
> I'm collecting JavaScript obfuscators for research purpose. Could any of
you
> name a few widely used ones? So far, I've tried Jsob and some free
> JavaScript obfuscators. Thanks.
>
> --Sophia
>

 

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