This bug was discovered back in december 2009, and patched by microsoft in April 2010.
This issue is a basic stack overflow affecting only windows 7/2008R2 smb1 implementation.
It's actually a nice bug as the affected function is not protected by a canary, and allow us to redirect the flow anywhere we want to.
You can find the full advisory about this bug here : http://seclists.org/fulldisclosure/2010/Apr/201
Have phun !
PoC url : http://pastebin.com/h3jSyJTN
Technical Rundown of WebExec
3 weeks ago