description = [[
Attempts to find an SNMP community string by brute force guessing.
]]
-- 2008-07-03
---
-- @args snmpcommunity The SNMP community string to use. If not supplied, this
-- script will not run.
-- @args snmplist The filename of a list of community strings to try.
--
-- @output
-- PORT STATE SERVICE
-- 161/udp open snmp
-- |_snmp-brute: public
author = "Philip Pickering"
license = "Same as Nmap--See http://nmap.org/book/man-legal.html"
categories = {"intrusive", "auth"}
require "shortport"
require "snmp"
portrule = shortport.portnumber(161, "udp", {"open", "open|filtered"})
action = function(host, port)
if nmap.registry.snmpcommunity or nmap.registry.args.snmpcommunity then return end
-- create the socket used for our connection
local socket = nmap.new_socket()
-- set a reasonable timeout value
socket:set_timeout(5000)
-- do some exception handling / cleanup
local catch = function()
socket:close()
end
local try = nmap.new_try(catch)
-- connect to the potential SNMP system
try(socket:connect(host, port))
local request = snmp.buildGetRequest({}, "1.3.6.1.2.1.1.3.0")
local commFile = nmap.registry.args.snmplist and nmap.fetchfile(nmap.registry.args.snmplist)
local commTable
-- fetch wordlist from file (from unpwdb-lib)
if commFile then
local file = io.open(commFile)
if file then
commTable = {}
while true do
local l = file:read()
if not l then
break
end
-- Comments takes up a whole line
if not l:match("#!comment:") then
table.insert(commTable, l)
end
end
file:close()
end
end
-- default wordlist
if (not commTable) then commTable = {'public', 'private', 'snmpd', 'snmp', 'mngt', 'cisco', 'admin'} end
-- send all possible words out before waiting for an answer
for _, commStr in ipairs(commTable) do
local payload = snmp.encode(snmp.buildPacket(request, 0, commStr))
try(socket:send(payload))
end
-- finally wait for a response
local status
local response
status, response = socket:receive_bytes(1)
if (not status) then
return
end
if (response == "TIMEOUT") then
return
end
nmap.set_port_state(host, port, "open")
local result
_, result = snmp.decode(response)
-- response contains valid community string
if type(result) == "table" then
nmap.registry.snmpcommunity = result[2]
return result[2]
end
return
end
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