shellcode with standard characters

[JohnnyRun <gianni79 () gamebox net>]

Hi!
This is my first post and I'm looking for some documentation.
A friend of mine has produced a segfault with malloc vulnerability on an
application.
We would like to produce something more interesting.
The field overflowed can accept only characters between 0 and 128. Any
other character is replaced with a whitespace.

Can we inject shellcode with only this characters avaible?
Can you suggest me documentation about shellcode writing?

Thanks a lot
JohnnyRun



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