Core Security Technologies Advisory
                             https://www.coresecurity.com

                     NetMeeting Directory Traversal Vulnerability



Date Published: 2003-07-02

Last Update: 2003-07-02

Advisory ID: CORE-2003-0305-04

Bugtraq ID: 7931

CVE Name: None currently assigned.

Title: NetMeeting Directory Traversal Vulnerability

Class: Input validation error

Remotely Exploitable: Yes

Locally Exploitable: No

Advisory URL:
  https://www.coresecurity.com/common/showdoc.php?idx=352&idxseccion=10

Vendors contacted:
  - Microsoft
    . Core Notification: 2003-05-21
    . Notification acknowledged by Microsoft: 2003-05-21
    . Issue fixed in Windows 2000 SP4: 2003-06-26

Release Mode: COORDINATED RELEASE


*Vulnerability Description:*

  Windows NetMeeting is a popular application used to hold audio and video
  conferences between a group of persons. One of its features is "File
  Transfer" which lets you send one or more files in the background
  during a NetMeeting conference.

  A directory traversal vulnerability was found in NetMeeting when
  doing File Transfers. An attacker can use filenames containing "..\..\"
  when doing a file transfer, and in this manner, create a file in any
  place of the victim's filesystem, escaping the directory where
  NetMeeting usually stores incoming files (e.g. C:\Program Files\
  Received\Received Files).

  This makes it possible to force the execution of arbitrary code on
  vulnerable systems.


*Vulnerable Packages:*

  NetMeeting version 3.01 (4.4.3385).
  Other versions may also be vulnerable.


*Solution/Vendor Information/Workaround:*

  A fix for this issue is included in Windows 2000 SP4 and Windows XP SP1
  available from:

  Windows 2000 Service Pack 4
  https://www.microsoft.com/Windows2000/downloads/servicepacks/sp4/

  Windows XP (Professional and Home edition) Service Pack 1
  https://www.microsoft.com/WindowsXP/pro/downloads/servicepacks/sp1/

  Windows Server 2003 does not ship with a vulnerable version of NetMeeting.


*Credits:*

  This vulnerability was found by Hernán Ochoa, Gustavo Ajzenman, Javier
  Garcia Di Palma and Pablo Rubinstein from Core Security Technologies
  during Bugweek 2003 (March 3-7, 2003).


*Technical Description - Exploit/Concept Code:*

  We have found a directory traversal vulnerability in NetMeeting when
  doing File Transfers. An attacker can use filenames containing "..\..\"
  when doing a file transfer, and in this manner, create a file in any
  place of the victim's filesystem, escaping the directory where
  NetMeeting usually stores incoming files (e.g.: C:\Program
  Files\Received\Received Files). An attacker cannot overwrite already
  existing files.

  A dialog box appears at the end of the file transfer, which can alert
  the user about the malicious action (the dialog box will not be
  automatically closed). However, the user is not prompted to reject or
  accept the file transfer, and since NetMeeting conferences can be
  shutdown by sending malformed packets (for example, by arbitrarily
  fuzzing data sent in packets interchanged during a chat conversation),
  the action can be hidden from the user. We're also investigating certain
  succession of packets that may prevent the dialog box from appearing
  at all.

  How to reproduce this vulnerability:

  - Start a NetMeeting conversation between two peers
  - Click on the "Transfer Files" button
  - Click on the "Add Files..." button and choose any file
    (e.g.: example_example_example.txt)
  - Attach a debugger to the NetMeeting process (conf.exe) and put a
    breakpoint on ws2_32!send
    (e.g.: ntsd -p <conf's pid> / bp send )
  - Click on the "Send All" button
  - The breakpoint set on ws2_32!send() will start popping up.
  - Examine the stack, and obtain the address of the buffer sent to the
    send() function, and examine its content
  - Look for the packet containing the name of the file being sent
    (e.g.: example_example_example.txt)
  - You're going to find two packets containing the filename, modify both
    packets with the debugger so that example_example_example.txt becomes
    ..\..\..\xample_example.txt
  - Let the process continue both times, and let the file transfer
    finish.
  - Now you can go to the root directory of the drive, and you'll see
    the file sent there instead of the "Received Files" directory.

  Of course, a debugger is not needed to exploit the vulnerability, it is
  just a convenient way to reproduce the vulnerability.

  We also found that by sending malformed packets in several different
  moments during a connection, all participants or a specific
  participant can be thrown out of the conversation. This is not a big
  issue per se, but it could help to hide malicious actions as the one
  described above (one can send the file, and immediately after, make the
  victim's NetMeeting drop the connection, which will make the dialog
  box of the file transfer disappear.)

  This vulnerability allows an attacker to execute arbitrary code.
  For instance, she can upload a specially crafted DLL with the name of
  one of the DLL's used by NetMeeting into the NetMeeting directory.
  The next time NetMeeting is executed, the system will try to load
  these DLL's first from the current directory, and then from
  C:\winnt\system32. So the system will load the attacker's DLL and
  execute arbitrary code upon the next execution of NetMeeting.
  Another possibility is to upload an executable file into the
  startup directory of win9x. That file will be executed the next
  time the user starts win9x.


*About Core Security Technologies*

  Core Security Technologies develops strategic security solutions for
  Fortune 1000 corporations, government agencies and military
  organizations. The company offers information security software and
  services designed to assess risk and protect and manage information
  assets.

  Headquartered in Boston, MA, Core Security Technologies can be reached
  at 617-399-6980 or on the Web at https://www.coresecurity.com.

  To learn more about CORE IMPACT, the first comprehensive penetration
  testing framework, visit:
  https://www.coresecurity.com/products/coreimpact


*DISCLAIMER:*

  The contents of this advisory are copyright (c) 2003 CORE Security
  Technologies and may be distributed freely provided that no fee is
  charged for this distribution and proper credit is given.

$Id: NetMeeting-advisory.txt,v 1.11 2003/07/02 15:45:46 carlos Exp $