Cisco User-Changeable Password XSS

Sunday, 16 March 2008

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Recurity Labs GmbH
http://www.recurity-labs.com
entomology@recurity-labs.com
Date: 12.03.2008
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Vendor:	               Cisco Systems
Product:               Cisco Secure Access Control Server (ACS) for 
                       Windows User-Changeable Password (UCP) application
Vulnerability:         Multiple remote pre-authentication buffer overflows
                       Cross Site Scripting issue
Affected Releases:     ACS 3 and 4, UCP v3.3.4.12.5, CSuserCGI 3.3.1
NOT Affected Releases: UCP 4.2 and above
Severity:              HIGH
CVE:                   CVE-2008-0532, CVE-2008-0533
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Vendor communication:
  20.11.2007           Initial notification to PSIRT
  20.11.2007           Response from PSIRT, PGP encrypted to PSIRT only
  26.11.2007           Response from Paul Oxman / PSIRT
  26.11.2007           Even more detailed information to Paul Oxman
  27.11.2007           Received new PGP keys from PSIRT
  27.11.2007           Retransmit
  28.11.2007           Paul Oxman reports they are working on it
  28.11.2007           Fix discussions with Paul Oxman
  29.11.2007           Paul Oxman provides Cisco Bug IDs
  29.11.2007           Fix discussions with Paul Oxman
  12.12.2007           Fixed version provided for testing
  13.12.2007           Feedback to the fixed code
  14.12.2007           Paul Oxman acknowledges feedback
  17.12.2007           Paul Oxman reports internal progress
  17.12.2007           More feedback 
  08.01.2008           Paul Oxman reports internal progress
  08.01.2008           ACK
  30.01.2008           Paul Oxman proposes advisory release date
  30.01.2008           Acknowleding advisory release date
  27.02.2008           Paul Oxman updates on progress
  27.02.2008           ACK
  05.03.2008           Paul Oxman sends draft Cisco advisory
  05.03.2008           Sending draft Recurity Labs advisory
  06.03.2008           Paul Oxman provides fixed release version
  06.03.2008           Final communication with Paul Oxman
  12.03.2008           Coordinated release
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Overview:
  Cisco Secure Access Control Server (ACS) for Windows User-Changeable 
  Password (UCP) application is a set of CGI programs and web site contents
  installed on Microsoft IIS.

  From the Cisco Advisory:
  "The UCP application enables end users to change their ACS passwords
  with a web-based utility. When users need to change their own
  passwords, they can access the UCP web page by using a supported web
  browser, validate their existing credentials, and then change their
  password via the utility."

  The CGI /securecgi-bin/CSUserCGI.exe suffers from multiple buffer
  overflows exploitable remotely through the HTTP protocol before
  authentication. Additionally, CSUserCGI.exe suffers from a non-persistent
  Cross Site Scripting vulnerability.

Description:
  The main() function of CSuserCGI.exe compares the first command line 
  argument passed to the program using strcmp() against a list of 
  supported arguments, among them "Logout", "Main", "ChangePass", etc. 

  For most of the aguments, it will simply parse the following arguments 
  and pass them to a wsprintf() call with format strings like 
  "Action=%s&Username=%s&OldPass=%s&NetPass=%s". The destination buffer of
  these calls is located in the .data segment of the application.

  In case of the "Logout" argument, main() passes the second argument,
  usually of the form "1234.xyzab.c.username.", as well as a char[] 
  buffer on the stack to a function that first extracts the string up 
  to the first '.' character using strtok and then copies the string 
  into the supplied char[] buffer. The char buffer is 96 bytes long.
  Accordingly, if the string before the first dot character exceeds this
  length, the buffer as well as the return address is overwritten.

  .text:00401065  mov     eax, [ebx+8]    ; get argv[2]
  .text:00401068  test    eax, eax
  .text:0040106A  jz      loc_401520
  .text:00401070  push    eax             ; char *
  .text:00401071  call    sub_402870
  ...
  .text:00402870  sub     esp, 60h
  .text:00402873  mov     ecx, 17h
  .text:00402878  xor     eax, eax
  .text:0040287A  push    edi
  .text:0040287B  lea     edi, [esp+64h+var_60]
  .text:0040287F  rep stosd
  .text:00402881  mov     ecx, [esp+64h+arg_0]
  .text:00402885  stosw
  .text:00402887  stosb
  .text:00402888  lea     eax, [esp+64h+var_60]
  .text:0040288C  push    eax             ; int
  .text:0040288D  push    ecx             ; char *
  .text:0040288E  call    sub_402940
  ...
  .text:00402940  mov     ecx, [esp+arg_0]
  .text:00402944  xor     eax, eax
  .text:00402946  test    ecx, ecx
  .text:00402948  jz      locret_402A11
  .text:0040294E  push    ebx
  .text:0040294F  push    esi
  .text:00402950  push    edi
  .text:00402951  push    offset a_       ; "."
  .text:00402956  push    ecx             ; char *
  .text:00402957  call    _strtok
  .text:0040295C  mov     edi, eax
  .text:0040295E  or      ecx, 0FFFFFFFFh
  .text:00402961  xor     eax, eax
  .text:00402963  mov     ebx, [esp+14h+arg_4]
  .text:00402967  repne scasb
  .text:00402969  not     ecx
  .text:0040296B  sub     edi, ecx
  .text:0040296D  lea     edx, [ebx+1]
  .text:00402970  mov     eax, ecx
  .text:00402972  mov     esi, edi
  .text:00402974  mov     edi, edx
  .text:00402976  push    offset a_       ; "."
  .text:0040297B  shr     ecx, 2
  .text:0040297E  rep movsd
  .text:00402980  mov     ecx, eax
  .text:00402982  push    0               ; char *
  .text:00402984  and     ecx, 3
  .text:00402987  rep movsb

Example:
  The following request will cause EIP to be overwritten with 0x42424242.
  The line may wrap, depending on how you view this file.
  https://target/securecgi-bin/CSUserCGI.exe?Logout+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABBBB.xyzab.c.hacker.

  A non-persistent Cross Site Scripting vulnerability can also be triggered
  using the Help facility of the CGI. An example request would be as
  follows. The line may wrap, depending on how you view this file.
  https://target/securecgi-bin/CSUserCGI.exe?Help+00.lala.c.hacker%22%22%22%3E%3Ch1%3EHello_Cisco%3C/h1%3E

Solution:
  Update to UCP version 4.2.
  See the Cisco Advisory for how to obtain fixed software:
  http://www.cisco.com/warp/public/707/cisco-sa-20080312-ucp.shtml
  
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Credit: 
  The vulnerabilities were identified by Felix 'FX' Lindner, Recurity Labs
  GmbH, during a cursory inspection of a customer installation of the ACS
  UCP product.

  Greets to the teams at Recurity Labs and Zynamics, Sergio Alvarez, Max
  Moser, Alexander Kornbrust, Maxim Salomon, Nicolas Fischbach, Karsten 
  Schumann, Frank Becker, PSIRT, Paul Oxman, John Stewart
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The information provided is released "as is" without warranty
of any kind. The publisher disclaims all warranties, either express or 
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is taken for the correctness of this information.
In no event shall the publisher be liable for any damages whatsoever 
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The contents of this advisory are copyright (c) 2008 Recurity Labs GmbH
and may be distributed freely provided that no fee is charged for this 
distribution and proper credit is given.
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