there is a (dumb) sock5 proxy preventing ssh 'exec' channel creation. so work around with ssh 'session' channel.

xssh.rb

require 'net/ssh'
require 'net/ssh/proxy/socks5'

def escape s
  # use ruby escpae, then replace double quote to single
  buf = s.inspect
  buf[0]="'"
  buf[-1]="'"
  buf
end

module XSSH
  class Connection
    def initialize(options={})
      proxy = options[:proxy] || {}
      socks5=Net::SSH::Proxy::SOCKS5.new(
                  proxy[:host], proxy[:port], 
                  :user => proxy[:user],
                  :password => proxy[:password])

      @session = Net::SSH.start(options[:host], 
                    options[:user],
                    :password=>options[:password],
                    :config=>false,
                    :verbose=>:fatal,
                    :proxy=>socks5)
      @prompt = options[:prompt]
      @buf = []
      @commands = []
      @session.open_channel do |channel|
        channel.on_data do |ch, data|
          print data
          STDOUT.flush
          @buf << data

          @output = @buf.join
          if Regexp.new(@prompt) =~ @output then
            @buf = []
            @state = :idle
          end
        end

        channel.on_process do |ch|
          if @state == :queue then
            cmd = @commands.shift
            channel.send_data "bash -c $#{escape cmd}\n"  
            @state = :sent
          end
        end
        channel.request_pty
        channel.send_channel_request "shell"
      end

      wait
    end

    def wait
      @session.loop { @state != :idle }
    end

    def queue cmd
      @commands << cmd
      @state = :queue
    end

    def queue_and_wait cmd
      queue cmd
      wait
      @output
    end

    attr_accessor :output
    def exec(cmd)
      queue_and_wait(cmd)
      

      queue_and_wait "echo $?"
      ret = @output.split("\r\n")[1].to_i

      wait
      ret
    end

    def close
      begin
        @session.close
      rescue Net::SSH::Disconnect => e
        # pass, not sure
      end
    end
  end
end