Use nmap to check current loaded ciphers.
Download
the file http://nmap.org/svn/scripts/ssh2-enum-algos.nse
|
local nmap = require "nmap"
local shortport = require
"shortport"
local stdnse = require
"stdnse"
local string = require
"string"
local table = require
"table"
local openssl = stdnse.silent_require
"openssl"
local ssh2 = stdnse.silent_require
"ssh2"
description = [[
Reports the number of algorithms (for
encryption, compression, etc.) that
the target SSH2 server offers. If
verbosity is set, the offered algorithms
are each listed by type.
If the "client to server"
and "server to client" algorithm lists are identical
(order specifies preference) then the
list is shown only once under a combined
type.
]]
---
-- @usage
-- nmap --script ssh2-enum-algos
target
--
-- @output
-- PORT STATE SERVICE
-- 22/tcp open ssh
-- | ssh2-enum-algos:
-- |
kex_algorithms (4)
-- | diffie-hellman-group-exchange-sha256
-- | diffie-hellman-group-exchange-sha1
-- | diffie-hellman-group14-sha1
-- | diffie-hellman-group1-sha1
-- |
server_host_key_algorithms (2)
-- | ssh-rsa
-- | ssh-dss
-- |
encryption_algorithms (13)
-- | aes128-ctr
-- | aes192-ctr
-- | aes256-ctr
-- | arcfour256
-- | arcfour128
-- | aes128-cbc
-- | 3des-cbc
-- | blowfish-cbc
-- | cast128-cbc
-- | aes192-cbc
-- | aes256-cbc
-- | arcfour
-- | rijndael-cbc@lysator.liu.se
-- |
mac_algorithms (6)
-- | hmac-md5
-- | hmac-sha1
-- | hmac-ripemd160
-- | hmac-ripemd160@openssh.com
-- | hmac-sha1-96
-- | hmac-md5-96
-- |
compression_algorithms (2)
-- | none
-- |_ zlib@openssh.com
--
-- @xmloutput
--
--
--
--
--
--
--
--
--
|
--
--
ssh-rsa
--
ecdsa-sha2-nistp256
--
--
--
aes128-ctr
--
aes192-ctr
--
aes256-ctr
--
aes128-cbc
--
3des-cbc
--
blowfish-cbc
--
cast128-cbc
--
aes192-cbc
--
aes256-cbc
--
--
--
hmac-sha1
--
umac-64@openssh.com
--
hmac-ripemd160
--
hmac-sha2-256
--
hmac-sha2-512
--
--
--
none
--
zlib@openssh.com
--
author = "Kris Katterjohn"
license = "Same as Nmap--See
http://nmap.org/book/man-legal.html"
categories = {"safe",
"discovery"}
portrule = shortport.port_or_service(22,
"ssh")
-- Build onto lists{} and possibly
modify parsed{} based on whether the
-- algorithm name-lists are identical
between the server-to-client and
-- client-to-server types. Note that this simply modifies the passed
tables.
local combine_types = function(parsed,
lists)
local doubles = {
"encryption_algorithms",
"mac_algorithms",
"compression_algorithms"
}
for _, i in ipairs(doubles) do
local c2s = i .. "_client_to_server"
local s2c = i .. "_server_to_client"
if parsed[c2s] == parsed[s2c] then
parsed[i] = parsed[c2s]
parsed[c2s] = nil
parsed[s2c] = nil
table.insert(lists, i)
else
table.insert(lists, c2s)
table.insert(lists, s2c)
end
end
end
-- Build and return the output table
local output = function(parsed, lists)
local out = stdnse.output_table()
for _, l in ipairs(lists) do
local v = parsed[l]
local a = v:len() > 0 and stdnse.strsplit(",", v) or {}
if nmap.verbosity() > 0 then
setmetatable(a, {
__tostring = function(t)
return
string.format("(%d)\n
%s", #t, table.concat(t, "\n "))
end
})
else
setmetatable(a, {
__tostring = function(t)
return
string.format("(%d)", #t)
end
})
end
out[l] = a
end
return out
end
action = function(host, port)
local sock = nmap.new_socket()
local status = sock:connect(host, port)
if not status then
return
end
status = sock:receive_lines(1)
if not status then
sock:close()
return
end
status = sock:send("SSH-2.0-Nmap-SSH2-Enum-Algos\r\n")
if not status then
sock:close()
return
end
local ssh = ssh2.transport
-- I would think that the server would send its kex data right after
-- receiving and verifying our protocol id string above, then we could
-- just use it here, but I've seen no definitive documentation saying
-- that we don't ever send ours first.
All I've seen is that if the
-- server doesn't care about compatibility with older clients then it
-- MAY send its kex data after the protocol id string. So I guess I'll
-- send it here until I know for sure (removing this send works
against
-- OpenSSH though).
local pkt = ssh.build(ssh.kex_init())
status = sock:send(pkt)
if not status then
sock:close()
return
end
local status, response = ssh.receive_packet(sock)
sock:close()
if not status then
return
end
local parsed = ssh.parse_kex_init(ssh.payload(response))
local lists = {
"kex_algorithms",
"server_host_key_algorithms"
-- Other types will be added below in combine_types()
}
-- Modifies tables
combine_types(parsed, lists)
return output(parsed, lists)
end
Run the
command.
|
[root@localhost ~]# nmap --script ssh2-enum-algo.nse
localhost
Starting Nmap 6.40 ( http://nmap.org )
at 2015-10-04 02:47 EDT
mass_dns: warning: Unable to determine
any DNS servers. Reverse DNS is disabled. Try using --system-dns or specify
valid servers with --dns-servers
Nmap scan report for localhost
(127.0.0.1)
Host is up (0.000010s latency).
Other addresses for localhost (not
scanned): 127.0.0.1
Not shown: 998 closed ports
PORT
STATE SERVICE
22/tcp open ssh
| ssh2-enum-algo:
|
kex_algorithms: (7)
|
ecdh-sha2-nistp256
|
ecdh-sha2-nistp384
|
ecdh-sha2-nistp521
|
diffie-hellman-group-exchange-sha256
|
diffie-hellman-group-exchange-sha1
|
diffie-hellman-group14-sha1
|
diffie-hellman-group1-sha1
|
server_host_key_algorithms: (2)
|
ssh-rsa
|
ecdsa-sha2-nistp256
|
encryption_algorithms: (15)
|
aes128-ctr
|
aes192-ctr
|
aes256-ctr
|
arcfour256
|
arcfour128
|
aes128-gcm@openssh.com
|
aes256-gcm@openssh.com
|
aes128-cbc
|
3des-cbc
|
blowfish-cbc
|
cast128-cbc
|
aes192-cbc
|
aes256-cbc
|
arcfour
|
rijndael-cbc@lysator.liu.se
|
mac_algorithms: (19)
|
hmac-md5-etm@openssh.com
|
hmac-sha1-etm@openssh.com
|
umac-64-etm@openssh.com
|
umac-128-etm@openssh.com
|
hmac-sha2-256-etm@openssh.com
|
hmac-sha2-512-etm@openssh.com
|
hmac-ripemd160-etm@openssh.com
|
hmac-sha1-96-etm@openssh.com
|
hmac-md5-96-etm@openssh.com
|
hmac-md5
|
hmac-sha1
|
umac-64@openssh.com
|
umac-128@openssh.com
|
hmac-sha2-256
|
hmac-sha2-512
|
hmac-ripemd160
|
hmac-ripemd160@openssh.com
|
hmac-sha1-96
|
hmac-md5-96
|
compression_algorithms: (2)
|
none
|_
zlib@openssh.com
25/tcp open smtp
Nmap done: 1 IP address (1 host up)
scanned in 2.46 seconds
|
Load only what is needed
Now we
specify the only ciphers that we need to load, hence removing those considered
weak.
In
sshd_config
|
Ciphers aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour
MACs
hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96
|
Test it
Restart
sshd and run the nmap script again to cross check, to diagnose,
|
$ ssh -vv -oCiphers=aes128-cbc,3des-cbc,blowfish-cbc
$ ssh -vv -oMACs=hmac-md5
|
If you
are testing with the ciphers or MACs that you have removed, you should be
getting something like this
|
no matching mac found: client hmac-sha1-etm@openssh.com server
hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96
|
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