author = "jah <jah@zadkiel.plus.com>"
license = "Same as Nmap--See http://nmap.org/book/man-legal.html"
categories = {"discovery"}
description = [[
Attempts to enumerate valid usernames on webservers running with the mod_userdir
module enabled.

The Apache mod_userdir module allows user-specific directories to be accessed
using the http://example.com/~user/ syntax.  This script makes http requests in
order to discover valid user-specific directories and infer valid usernames.  By
default, the script will use Nmaps nselib/data/usernames.lst  An http response
status of 200 or 403 means the username is likely a valid one and the username
will be output in the script results along with the status code (in parentheses).

This script makes an attempt to avoid false positives by requesting a directory
which is unlikely to exist.  If the server responds with 200 or 403 then the
script will not continue testing it.

Ref: CVE-2001-1013 http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2001-1013
]]
---
-- @args
-- users=path/to/custom/usernames.list or
-- userdir.users=path/to/custom/usernames.list
--
-- @output
-- 80/tcp open  http    syn-ack Apache httpd 2.2.9
-- |_ apache-userdir-enum: Potential Users: root (403), user (200), test (200)



local http      = require 'http'
local stdnse    = require 'stdnse'
local datafiles = require 'datafiles'



---
-- The script will run against http[s] and http[s]-alt ports and, if version
-- detection is performed, will run only against targets likely to be using
-- mod_userdir or similar.
portrule = function(host, port)
  local svc = { std = { ["http"] = 1, ["http-alt"] = 1 },
                ssl = { ["https"] = 1, ["https-alt"] = 1 } }
  if port.protocol ~= 'tcp' or not
  ( svc.std[port.service] or svc.ssl[port.service] ) then
    return false
  end
  -- Don't bother running on SSL ports if we don't have SSL.
  if (svc.ssl[port.service] or port.version.service_tunnel == 'ssl') and not
  nmap.have_ssl() then
    return false
  end
  -- Reduce execution to likely targets when version detection was performed
  if port.version and port.version.product then
    local v = port.version
    if v.product:lower():match('apache') and
    not ( v.product:lower():match('tomcat') or v.product:lower():match('coyote') ) then
      return true
    elseif v.product:lower():match('lighttpd') then
      return true
    elseif v.product:lower():match('nginx') then
      return true -- unlikely! no userdir module for nginx, but config can emulate it.
    elseif v.extrainfo and v.extrainfo:lower():match('based on apache') then
      return true
    else
      return false
    end
  end
  return true
end



action = function(host, port)

  if not nmap.registry.userdir then init() end
  local usernames = nmap.registry.userdir
  if #usernames == 0 then return nil end  -- speedy exit if no usernames

  local filename = filename:match( "[\\/]([^\\/]+)\.nse$" )
  local hname = host.targetname or ( host.name ~= '' and host.name ) or host.ip
  local found = {}

  for i, uname in ipairs(usernames) do

    local data = http.get( host, port, ("/~%s/"):format(uname) )
    if data and type(data.status) == 'number' then
      if (data.status == 403 or data.status == 200) and i == 1 then
        -- This server is unlikely to yield useful information since it returned
        -- 200 or 403 to a request for a directory which is highly unlikely to exist.
        stdnse.print_debug(1, "%s detected false positives at %s:%d - status was %d",
          filename, hname, port.number, data.status)
        break
      elseif data.status == 403 or data.status == 200 then
        found[#found+1] = ("%s (%d)"):format(uname, data.status)
      -- else we didn't get an interesting status code
      end
    else
      stdnse.print_debug(2, "%s got a bad or zero response from %s:%d",
        filename, hname, port.number)
    end

  end

  if #found == 0 then
    stdnse.print_debug(2, "%s found Zero users at %s:%d",
      filename, hname, port.number)
    return nil
  end

  return ("Potential Users: %s"):format(table.concat(found, ", "))

end



---
-- Parses a file containing usernames (1 per line), defaulting to
-- "nselib/data/usernames.lst" and stores the resulting array of usernames in
-- the registry for use by all threads of this script.  This means file access
-- is done only once per Nmap invocation.  init() also adds a random string to
-- the array (in the first position) to attempt to catch false positives.
-- @return nil

function init()
  local filename = filename and filename:match( "[\\/]([^\\/]+)\.nse$" ) or ""
  local customlist = nmap.registry.args.users or
    (nmap.registry.args.userdir and nmap.registry.args.userdir.users) or
    nmap.registry.args['userdir.users']
  local read, usernames = datafiles.parse_file(customlist or "nselib/data/usernames.lst", {})
  if not read then
    stdnse.print_debug(1, "%s %s", filename,
      usernames or "Unknown Error reading usernames list.")
    nmap.registry.userdir = {}
    return nil
  end
  -- random dummy username to catch false positives
  if #usernames > 0 then table.insert(usernames, 1, randomstring()) end
  nmap.registry.userdir = usernames
  stdnse.print_debug(1, "%s Testing %d usernames.", filename, #usernames)
  return nil
end



---
-- Uses openssl.rand_pseudo_bytes (if available, os.time() if not) and base64.enc
-- to produce a randomish string of at least 11 alphanumeric chars.
-- @return String

function randomstring()
  local bin    = require"bin"
  local base64 = require"base64"
  local rnd, s, l, _
  if pcall(require, "openssl") then
    rnd = openssl.rand_pseudo_bytes
  end
  s = rnd and rnd(8) or tostring( os.time() )
  -- increase the length of the string by 0 to 7 chars
  _, l = bin.unpack(">C", s, 8) -- eighth byte should be safe for os.time() too
  s = l%8 > 0 and s .. s:sub(1,l%8) or s
  -- base 64 encode and replace any non alphanum chars (with 'n' for nmap!)
  s = base64.enc(s):sub(1,-2):gsub("%W", "n")
  return s
end