BoF in Windows 2000: ddeshare.exe

[Jack C <jack () crepinc com>]

Hello all,

I found a static buffer overflow in ddeshare.exe on my Windows 2000, 
latest updates/service packs box tonight. It appears as though no bounds 
checking is performed on the share name before it is copied to the variable.

Exploiting:
Start up c:\winnt\system32\ddeshare.exe. Click shares --> trusted 
shares. Pick any of the shares already there (at least there are some on 
my box, if not you can make one), and select Properties. Replace the 
data in the "Share Name" text box with something like this:

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABB

When you click OK, you get an error stating that ddeshare.exe has 
"generated errors". Yay.

Run in OllyDbg, we find that the above string makes the program attempt 
to JMP to 0x00420042. It just so happens that Hex 42 is a "B". So the 
two B's at the end of the exploit string change the instrucation pointer.

As far as I can tell, this is not exploitable to run a shellcode because 
of the fact that NULL's are inserted between charactors. But besides 
that, it would only give the same privliges that you already have to run 
the program in the first place. It simply points out bad coding.

Again, this isn't another of Microsoft's giant end-of-the-world security 
blunders, but still, it's a BoF.

Thanks,

-Jack C ("crEp")
jack [at] crepinc.com
http://www.crepinc.com