Fix Net::SSH::CommandStream session open failure

I suspected this might be a problem for libssh servers.

documentation/modules/auxiliary/scanner/ssh/libssh_auth_bypass.md

@@ -122,7 +122,14 @@ msf5 auxiliary(scanner/ssh/libssh_auth_bypass) > run
 
 [*] 172.28.128.3:2222 - Attempting authentication bypass
 [+] 172.28.128.3:2222 - SSH-2.0-libssh_0.8.3 appears to be unpatched
-[-] 172.28.128.3:2222 - shell/exec channel request failed
+[-] 172.28.128.3:2222 - Net::SSH::ChannelOpenFailed: Session channel open failed (1)
+[*] Scanned 1 of 1 hosts (100% complete)
+[*] Auxiliary module execution completed
+msf5 auxiliary(scanner/ssh/libssh_auth_bypass) > run
+
+[*] 172.28.128.3:2222 - Attempting authentication bypass
+[+] 172.28.128.3:2222 - SSH-2.0-libssh_0.8.3 appears to be unpatched
+[-] 172.28.128.3:2222 - Net::SSH::ChannelRequestFailed: Shell/exec channel request failed
 [*] Scanned 1 of 1 hosts (100% complete)
 [*] Auxiliary module execution completed
 msf5 auxiliary(scanner/ssh/libssh_auth_bypass) >

lib/net/ssh/command_stream.rb

@@ -1,10 +1,6 @@
 # -*- coding: binary -*-
-require 'rex'
 
-module Net
-module SSH
-
-class CommandStream
+class Net::SSH::CommandStream
 
   attr_accessor :channel, :thread, :error, :ssh
   attr_accessor :lsock, :rsock, :monitor
@@ -17,9 +13,11 @@ class CommandStream
 
   def shell_requested(channel, success)
     unless success
-      raise Net::SSH::ChannelRequestFailed, 'shell/exec channel request failed'
+      raise Net::SSH::ChannelRequestFailed, 'Shell/exec channel request failed'
     end
 
+    self.channel = channel
+
     channel[:data] = ''
     channel[:extended_data] = ''
 
@@ -40,8 +38,6 @@ class CommandStream
       self.rsock.write(data)
       channel[:extended_data] << data
     end
-
-    self.channel = channel
   end
 
   def initialize(ssh, cmd = nil, pty: false, cleanup: false)
@@ -52,44 +48,39 @@ class CommandStream
 
     self.ssh = ssh
     self.thread = Thread.new(ssh, cmd, pty, cleanup) do |rssh, rcmd, rpty, rcleanup|
-      begin
-        info = rssh.transport.socket.getpeername_as_array
-        self.lsock.peerinfo  = "#{info[1]}:#{info[2]}"
+      info = rssh.transport.socket.getpeername_as_array
+      self.lsock.peerinfo  = "#{info[1]}:#{info[2]}"
 
-        info = rssh.transport.socket.getsockname
-        self.lsock.localinfo = "#{info[1]}:#{info[2]}"
+      info = rssh.transport.socket.getsockname
+      self.lsock.localinfo = "#{info[1]}:#{info[2]}"
 
-        rssh.open_channel do |rch|
-          # A PTY will write us to {u,w}tmp and lastlog
-          rch.request_pty if rpty
-          if rcmd.nil?
-            rch.send_channel_request('shell', &method(:shell_requested))
-          else
-            rch.exec(rcmd, &method(:shell_requested))
-          end
+      channel = rssh.open_channel do |rch|
+        # A PTY will write us to {u,w}tmp and lastlog
+        rch.request_pty if rpty
+
+        if rcmd.nil?
+          rch.send_channel_request('shell', &method(:shell_requested))
+        else
+          rch.exec(rcmd, &method(:shell_requested))
         end
+      end
 
-        self.monitor = Thread.new do
-          while(true)
-            next if not self.rsock.has_read_data?(1.0)
-            buff = self.rsock.read(16384)
-            break if not buff
-            verify_channel
-            self.channel.send_data(buff) if buff
-          end
+      channel.on_open_failed do |ch, code, desc|
+        raise Net::SSH::ChannelOpenFailed.new(code, 'Session channel open failed')
+      end
+
+      self.monitor = Thread.new do
+        while(true)
+          next if not self.rsock.has_read_data?(1.0)
+          buff = self.rsock.read(16384)
+          break if not buff
+          verify_channel
+          self.channel.send_data(buff) if buff
         end
+      end
 
-        while true
-          rssh.process(0.5) { true }
-        end
-
-      rescue ::Exception => e
-        # XXX: This won't be set UNTIL there's a failure from a thread
-        self.error = e
-        #::Kernel.warn "BOO: #{e.inspect}"
-        #::Kernel.warn e.backtrace.join("\n")
-      ensure
-        self.monitor.kill if self.monitor
+      while true
+        rssh.process(0.5) { true }
       end
 
       # Shut down the SSH session if requested
@@ -97,6 +88,11 @@ class CommandStream
         rssh.close
       end
     end
+  rescue ::Exception => e
+    # XXX: This won't be set UNTIL there's a failure from a thread
+    self.error = e
+  ensure
+    self.monitor.kill if self.monitor
   end
 
   #
@@ -118,6 +114,3 @@ class CommandStream
   end
 
 end
-end
-end
-

modules/auxiliary/scanner/ssh/libssh_auth_bypass.rb

@@ -130,8 +130,8 @@ class MetasploitModule < Msf::Auxiliary
     # XXX: Wait for CommandStream to log a channel request failure
     sleep 0.1
 
-    if shell.error
-      print_error("#{ip}:#{rport} - #{shell.error}")
+    if (e = shell.error)
+      print_error("#{ip}:#{rport} - #{e.class}: #{e.message}")
       return
     end
 
@@ -139,10 +139,10 @@ class MetasploitModule < Msf::Auxiliary
     when 'Shell'
       start_session(self, "#{self.name} (#{version})", {}, false, shell.lsock)
     when 'Execute'
-      output = shell.channel[:data].chomp
+      output = shell.channel && (shell.channel[:data] || '').chomp
 
       if output.blank?
-        print_error("Empty or blank output: #{datastore['CMD']}")
+        print_error("#{ip}:#{rport} - Empty or blank command output")
         return
       end