Javascript long string detection

Hi,

I have come across this vulnerability

http://nvd.nist.gov/nvd.cfm?cvename=CVE-2008-0729

and corresponding Exploit at

http://www.milw0rm.org/exploits/5268

There are so many ways to create a long string in Javascript.  How do
Network based IDS/IPS can detect these kinds of attacks?  Is it
possible to create signatures to detect these attacks?   Many existing
IDS/IPS devices don't have capabilities to interpret and evaluate
javascripts. So, I would think that it is nearly impossible.  Any
insight?

Thanks
Ravi

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