Re: [funsec] Technical Paper on the ZERT Patch and VML [was: Re: ZERT patch for setSlice()]

[Alexander Sotirov <asotirov () determina com>]

Gadi Evron wrote:
> Our (ZERT's) VML patch was what you refer to as "real". There was space
> issue with not enough bytes to play with, so Gil Dabah, one of our
> members, re-wrote the vulnerable function in Yasm, compiled it, and
> hard-coded the compiled code into the binary, with room to spare, saving
> functionality. Code crunching is back in style. :)

Rewriting the entire function in asm is a lot of unnecessary effort. Why didn't
you add a simple length check and a 5-byte jump to it in the vulnerable function?

Patch right before the call to _IE5_SHADETYPE_TEXT::TOKENS::Ptok, check the
length of the string, and you're done. Or you can patch the copy loop and count
the characters there. It's easier and safer than rewriting the function.

Alex