ssh-auth-methods

NSE detection rule by Devin Bjelland · Same as Nmap--See https://nmap.org/book/man-legal.html

Returns authentication methods that a SSH server supports. This is in the "intrusive" category because it starts an authentication with a username which may be invalid. The abandoned connection will likely be logged.

local shortport = require "shortport"
local stdnse = require "stdnse"
local libssh2_util = require "libssh2-utility"
local rand = require "rand"

description = [[
Returns authentication methods that a SSH server supports.

This is in the "intrusive" category because it starts an authentication with a
username which may be invalid. The abandoned connection will likely be logged.
]]

---
-- @usage
--  nmap -p 22 --script ssh-auth-methods --script-args="ssh.user=<username>" <target>
--
-- @output
-- 22/tcp open  ssh     syn-ack
-- 22/tcp open  ssh     syn-ack
-- | ssh-auth-methods:
-- |   Supported authentication methods:
-- |     publickey
-- |     password
-- |   Banner: This is a private system. Use of this system constitutes
-- |_consent to monitoring.
--
-- @xmloutput
-- <table key="Supported authentication methods">
--   <elem>publickey</elem>
--   <elem>password</elem>
-- </table>
-- <elem key="Banner">This is a private system. Use of this system constitutes&#xa;consent to monitoring.&#xa;</elem>

author = "Devin Bjelland"
license = "Same as Nmap--See https://nmap.org/book/man-legal.html"
categories = {"auth", "intrusive"}

local username = stdnse.get_script_args("ssh.user") or rand.random_alpha(5)
portrule = shortport.ssh

function action (host, port)
  local result = stdnse.output_table()
  local helper = libssh2_util.SSHConnection:new()
  local status, err = helper:connect_pcall(host, port)
  if not status then
    return "Failed to connect to ssh server: " .. err
  end

  local authmethods = helper:list(username)

  result["Supported authentication methods"] = authmethods
  result["Banner"] = helper:banner()

  return result
end

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ee150adf-b078-4cae-bf54-cb052f152810

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Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

Rejected pattern present

[[ reason ]]

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Format & documentation suggestions

Not a security issue — this rule is valid and was accepted as-is. These are optional fields/conventions its own format recommends, mainly affecting its quality score and how well it documents itself for other reviewers.

[[ reason ]]

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