Re: Microsoft Windows XP/2003/Vista memory corruption 0day

[3APA3A <3APA3A () SECURITY NNOV RU>]

Dear Alexander Sotirov,


AS> The  HardError  message  is handled by the UserHardError function in
AS> WINSRV.DLL. It calls GetHardErrorText to read the message parameters
AS> from  the address space of the sender. The GetHardErrorText function
AS> returns  pointers to the caption and text of the message box. If the
AS> caption  or text parameters start with the \??\ prefix, the function
AS> inexplicably frees the buffer and returns a pointer to freed memory.
AS> After  the  message  box  is  closed by the user, the same buffer is
AS> freed  again  in  the  FreePhi  function, resulting in a double free
AS> vulnerability.

I  may  be  wrong, but probably this fact doesn't explain the garbage on
the  screen in MessageBox. Even "use after free()" vulnerability doesn't
explain  it, because garbage is permanent. There should be some more bug
before second free().


--Thursday, December 21, 2006, 11:11:29 PM, you wrote to 3APA3A () SECURITY NNOV RU:

AS> 3APA3A wrote:
> > Killer{R}  assumes  the problem is in strcpy(), because it should not be
> > used for overlapping buffers, but at least ANSI implementation of strcpy
> > from  Visual  C  should be safe in this very situation (copying to lower
> > addresses).  May be code is different for Windows XP or vulnerability is
> > later in code.

AS> We discovered this bug some time ago and were preparing an advisory when it was
AS> publicly disclosed. Since the exploit is already public, here's my analysis of
AS> the vulnerability:

AS> http://www.determina.com/security.research/vulnerabilities/csrss-harderror.html

AS> It's a double free bug that leads to arbitrary code execution in the CSRSS process.

AS> Alex


-- 
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