:. 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 <[email protected]>
• 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