ASP.DLL Include File Buffer Overflow Jul 18 2006 10:09PM
Brett Moore (brett moore security-assessment com)

= ASP.DLL Include File Buffer Overflow
= MS Bulletin posted:
= http://www.microsoft.com/technet/security/Bulletin/MS06-034.mspx
= Affected Software:
= IIS 5.0
= IIS 5.1
= IIS 6.0
= Public disclosure on July 19, 2006

== Overview ==

A buffer overflow exists in ASP.DLL that can be exploited by creating
a .asp file containing a parameter for the include SSI command.

<!-- #include file="<long buffer>" -->OVERFLOWDATA

The include function in ASP.DLL, checks if the parameter is longer than
260 bytes. If it is then an error is caused, but before causing the
a miscalculated copy is done.

mov edi, [ebp+var_228] ; load length of parameter
cmp edi, 104h ; check if larger than 260 bytes
jbe short loc_
mov esi, [ebp+var_22C] ; load address of parameter
lea eax, [edi+esi-104h] ; load eax with the address of the last
; 260 bytes of the parameter
; (length of string+source of string)-
lea edx, [ebp+var_211] ; load edx with address on stack
sub edx, eax ;
mov cl, [eax] ; mov [edx+eax], cl ; do the copy
inc eax ; and overflow the stack
test cl, cl ; /
jnz short loc_7096D1F3 ;

Funnily enough, the solution was to remove this copy as the resulting
data was never actually used.

== Exploitation ==

Exploitation requires the ability to upload or somehow create a file
a .asp extension in a folder that will allow .asp processing.

Since ASP.DLL usually runs under the IWAM_ account, there is no
escalation through this vulnerability. It is however possible to bypass
any security restrictions enforced by ASP. It also allows for the
execution of APIS that have no ASP equivalent.

== Solutions ==

- Install the vendor supplied patch.

== Credit ==

Discovered and advised to Microsoft February, 2006 by Brett Moore of

Same Bug Different App

In memory of;

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