full-disclosure - RE: Unchecked buffer in mstask.dll

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From: nick at virus-l.demon.co.uk (Nick FitzGerald)
Subject: RE: Unchecked buffer in mstask.dll

"Jordan Cole (stilist)" <stilist@...il.com> to Paul Szabo:

> > Being curious, on Win2k, I copied cmd.exe (from winnt\system32) as xyz.pif;
> > then (right-click) Properties, Program crashes explorer.

I had to specifically click on the "Program" tab, which evoked a null-
pointer read attempt (at a guess, something in the .PIF parser assumes 
a length or offset will always be >0 so doesn't do any sanity checking, 
and/or some higher level routines don't do any checking).

> I'd say that's because you changed the filetype; pif files simply
> contain information on how to handle a DOS executable; they aren't a
> program themselves. All you did was make it get confused and kill
> itself.

Yeah, but how long is it now since we've been telling programmers 
"don't trust user-supplied data"??  (Hmmmm -- does it also fail on 
W2K3??)

And don't you also find the inconsistencies this throws up at least 
somewhat interesting?

Rename a PE executable to a .PIF extension, right click, ask to see the 
file's properties and splat -- whatever code is invoked to handle that 
task dies a stupid, if not ugly, death because internally the file is 
the wrong type.  However, if you double-click that renamed file it is  
executed as if nothing is amiss.

And to think that some folk will see this as further reason to enforce 
their belief that when it comes to security and code quality, Microsoft 
really just doesn't get it...

Why did MS make ".EXE files renamed as .PIF" execute "properly"?  Aside 
from "because we can", I'd not be at all surprised if it was on some 
internal "stupid user tricks we should eliminate support calls for" 
list.  But, whatever the reason, did anyone at Microsoft give two 
milliseconds of thought to the security (or other) consequences of that 
design decision?  I seriously doubt it and I'm sure I'm far from alone 
in that...

-- 
Nick FitzGerald
Computer Virus Consulting Ltd.
Ph/FAX: +64 3 3529854