From: GOODFELLAS SRT (goodfellasshellcode.com.ar)
Date: Fri Jun 22 2007 - 15:41:55 CDT

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:. GOODFELLAS Security Research TEAM .:
:. http://goodfellas.shellcode.com.ar .:

BarCodeAx.dll v. 4.9 ActiveX Control Remote Stack Buffer Overflow
=================================================================
Internal ID: VULWAR200706223

Introduction
------------
BarCodeAx.dll is a library included in the Barcode ActiveX software
package from the Company RKD:
(http://www.barcodetools.com/barcode/barcode-activex/barcode-activex.html)

Such package allows to manage the printing of different barcodes.

One of the BarcodeAx.dll exported methods is vulnerable to a stack
buffer overflow which can be remotely exploited.

tested in
---------
- Windows XP SP2 english/french with IE 6.0 / 7.0
- windows vista Professional SP1 with IE 7.0

Summary
-------
The BeginPrint method fail to correctly check the size of the arguments
that receives, causing a stack buffer overflow.

Impact
------
Any application that uses the said ActiveX to control barcodes would be
exposed to remote code execution.

Workaround
----------
- Activate the Kill bit zero in
CLSID:C26D9CA8-6747-11D5-AD4B-C01857C10000
- Unregister BarCodeAx.dll using regsvr32

Timeline
--------
June 21, 2007 -- Bug discovery
June 22, 2007 -- Bug published

Credits
-------
 * Brian Mariani <bmarianishellcode.com.ar>
 * GoodFellas Security Research Team <goodfellas.shellcode.com.ar>

Technical Detail
----------------

Vulnerable method.

Sub BeginPrint (
         ByVal name As String
)

We need 656 bytes to overflow the buffer and rewrite EBP + EIP.

- Reversing
7C97DF40 PUSH 0
7C97DF42 PUSH ESI
7C97DF43 CALL 7C97CDC9
7C97DF48 MOV EBX,[EBP+10]
7C97DF4B LEA EDI,[EBX-8]
7C97DF4E MOV [EBP-2C],EDI
7C97DF51 MOVZX EAX,WORD PTR [EDI] <--- CRASH
7C97DF54 SHL EAX,3
7C97DF57 MOV [EBP-30],EAX
7C97DF5A PUSH 7C97E11C
7C97DF5F PUSH EDI
7C97DF60 PUSH ESI
7C97DF61 CALL 7C97CC6D
7C97DF66 TEST AL,AL
7C97DF68 JE 7C97E0BF

- Registers
EIP 41414141
EAX C0040204
EBX 00407830 -> 003E977D
ECX 0013ECE8 -> Asc: AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
EDX 00150608 -> 7C98C500
EDI 00000000
ESI 001844CC -> 00180008
EBP 41414141
ESP 0013EBE8 -> Asc: AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

--
GOODFELLAS (Shellcode Security Research)
http://goodfellas.shellcode.com.ar

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