[NT] NetMeeting Directory Traversal Vulnerability
From: SecuriTeam (support_at_securiteam.com)
To: firstname.lastname@example.org Date: 6 Jul 2003 20:09:44 +0200
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NetMeeting Directory Traversal Vulnerability
Windows NetMeeting is a popular application used to hold audio and video
conferences between groups of people. One of its features is "File
Transfer" which lets you send one or more files in the background during a
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
* NetMeeting version 3.01 (4.4.3385). Other versions may also be
CORE has 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 file system, 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.:
- 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.:
- You're going to find two packets containing the filename, modify both
packets with the debugger so that example_example_example.txt becomes
- 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.
CORE 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
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.
The fix for this issue is included in Windows 2000 SP4 and Windows XP SP1
Windows XP (Professional and Home edition) Service Pack 1
Windows Server 2003 does not ship with a vulnerable version of NetMeeting.
. Core Notification: 2003-05-21
. Notification acknowledged by Microsoft: 2003-05-21
. Issue fixed in Windows 2000 SP4: 2003-06-26
The original advisory can be downloaded from:
The information has been provided by <mailto:firstname.lastname@example.org>
CORE Security Technologies Advisories.
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