rspamd/rules/misc.lua

--[[
Copyright (c) 2011-2015, Vsevolod Stakhov <vsevolod@highsecure.ru>

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
]]--

-- This is main lua config file for rspamd

local util = require "rspamd_util"
local rspamd_regexp = require "rspamd_regexp"
local rspamd_logger = require "rspamd_logger"

local reconf = config['regexp']

-- Uncategorized rules
local subject_re = rspamd_regexp.create('/^(?:(?:Re|Fwd|Fw|Aw|Antwort|Sv):\\s*)+(.+)$/i')

-- Local rules
local r_bgcolor = '/BGCOLOR=/iP'
local r_font_color = '/font color=[\\"\']?\\#FFFFFF[\\"\']?/iP'
reconf['R_WHITE_ON_WHITE'] = string.format('(!(%s) & (%s))', r_bgcolor, r_font_color)
reconf['R_FLASH_REDIR_IMGSHACK'] = '/^(?:http:\\/\\/)?img\\d{1,5}\\.imageshack\\.us\\/\\S+\\.swf/U'

-- Local functions


-- Subject issues
local function test_subject(task, check_function, rate)
  local function normalize_linear(a, x)
      local f = a * x
      return true, (( f < 1 ) and f or 1), tostring(x)
  end

  local sbj = task:get_header('Subject')

  if sbj then
    local stripped_subject = subject_re:search(sbj, false, true)
    if stripped_subject and stripped_subject[1] and stripped_subject[1][2] then
      sbj = stripped_subject[1][2]
    end

    local l = util.strlen_utf8(sbj)
    if check_function(sbj, l) then
      return normalize_linear(rate, l)
    end
  end

  return false
end

rspamd_config.SUBJ_ALL_CAPS = {
  callback = function(task)
    local caps_test = function(sbj, len)
      return util.is_uppercase(sbj)
    end
    return test_subject(task, caps_test, 1.0/40.0)
  end,
  score = 3.0,
  group = 'subject',
  description = 'All capital letters in subject'
}

rspamd_config.LONG_SUBJ = {
  callback = function(task)
    local length_test = function(sbj, len)
      return len > 200
    end
    return test_subject(task, length_test, 1.0/400.0)
  end,
  score = 3.0,
  group = 'subject',
  description = 'Subject is too long'
}

-- Different text parts
rspamd_config.R_PARTS_DIFFER = function(task)
  local distance = task:get_mempool():get_variable('parts_distance', 'double')

  if distance then
    local nd = tonumber(distance)
    -- ND is relation of different words to total words
    if nd >= 0.5 then
      local tw = task:get_mempool():get_variable('total_words', 'int')

      if tw then
        local score
        if tw > 30 then
          -- We are confident about difference
          score = (nd - 0.5) * 2.0
        else
          -- We are not so confident about difference
          score = (nd - 0.5)
        end
        task:insert_result('R_PARTS_DIFFER', score,
          string.format('%.1f%%', tostring(100.0 * nd)))
      end
    end
  end

  return false
end

-- Date issues
rspamd_config.MISSING_DATE = function(task)
	if rspamd_config:get_api_version() >= 5 then
		local date = task:get_header_raw('Date')
		if date == nil or date == '' then
			return true
		end
	end

	return false
end
rspamd_config.DATE_IN_FUTURE = function(task)
	if rspamd_config:get_api_version() >= 5 then
		local dm = task:get_date{format = 'message'}
		local dt = task:get_date{format = 'connect'}
		-- An 2 hour
		if dm > 0 and dm - dt > 7200 then
			return true
		end
	end

	return false
end
rspamd_config.DATE_IN_PAST = function(task)
	if rspamd_config:get_api_version() >= 5 then
    local dm = task:get_date{format = 'message', gmt = true}
    local dt = task:get_date{format = 'connect', gmt = true}
		-- A day
		if dm > 0 and dt - dm > 86400 then
			return true
		end
	end

	return false
end

rspamd_config.R_SUSPICIOUS_URL = function(task)
    local urls = task:get_urls()

    if urls then
      for i,u in ipairs(urls) do
        if u:is_obscured() then
          task:insert_result('R_SUSPICIOUS_URL', 1.0, u:get_host())
        end
      end
    end
    return false
end

rspamd_config.BROKEN_HEADERS = {
  callback = function(task)
    if task:has_flag('broken_headers') then
      return true
    end

    return false
  end,
  score = 1.0,
  group = 'header',
  description = 'Headers structure is likely broken'
}

rspamd_config.HEADER_RCONFIRM_MISMATCH = {
  callback = function (task)
    local header_from = nil
    local cread = task:get_header('X-Confirm-Reading-To')

    if task:has_from('mime') then
      header_from  = task:get_from('mime')[1]
    end

    local header_cread = nil
    if cread then
      local headers_cread = util.parse_mail_address(cread)
      if headers_cread then header_cread = headers_cread[1] end
    end

    if header_from and header_cread then
      if not string.find(header_from['addr'], header_cread['addr']) then
        return true
      end
    end

    return false
  end,

  score = 2.0,
  group = 'header',
  description = 'Read confirmation address is different to from address'
}

rspamd_config.HEADER_FORGED_MDN = {
  callback = function (task)
    local mdn = task:get_header('Disposition-Notification-To')
    local header_rp = nil

    if task:has_from('smtp') then
      header_rp = task:get_from('smtp')[1]
    end

    -- Parse mail addr
    local header_mdn = nil
    if mdn then
      local headers_mdn = util.parse_mail_address(mdn)
      if headers_mdn then header_mdn = headers_mdn[1] end
    end

    if header_mdn and not header_rp  then return true end
    if header_rp  and not header_mdn then return false end

    if header_mdn and header_mdn['addr'] ~= header_rp['addr'] then
      return true
    end

    return false
  end,

  score = 2.0,
  group = 'header',
  description = 'Read confirmation address is different to return path'
}

local headers_unique = {
  'Content-Type',
  'Content-Transfer-Encoding',
  -- https://tools.ietf.org/html/rfc5322#section-3.6
  'Date',
  'From',
  'Sender',
  'Reply-To',
  'To',
  'Cc',
  'Bcc',
  'Message-ID',
  'In-Reply-To',
  'References',
  'Subject'
}

rspamd_config.MULTIPLE_UNIQUE_HEADERS = {
  callback = function (task)
    local res = 0
    local res_tbl = {}

    for i,hdr in ipairs(headers_unique) do
      local h = task:get_header_full(hdr)

      if h and #h > 1 then
        res = res + 1
        table.insert(res_tbl, hdr)
      end
    end

    if res > 0 then
      return true,res,table.concat(res_tbl, ',')
    end

    return false
  end,

  score = 5.0,
  group = 'header',
  description = 'Repeated unique headers'
}

rspamd_config.ENVFROM_PRVS = {
    callback = function (task)
        -- Detect PRVS/BATV addresses to avoid FORGED_SENDER
        -- https://en.wikipedia.org/wiki/Bounce_Address_Tag_Validation
        if not (task:has_from(1) and task:has_from(2)) then
            return false
        end
        local envfrom = task:get_from(1)
        local tag,ef = envfrom[1].addr:lower():match("^prvs=([^=]+)=(.+)$")
        if not ef then return false end
        -- See if it matches the From header
        local from = task:get_from(2)
        if ef == from[1].addr:lower() then
            return true
        end
        return false
    end,
    score = 0.01,
    description = "Envelope From is a PRVS address that matches the From address",
    group = 'prvs'
}

rspamd_config.ENVFROM_VERP = {
    callback = function (task)
        if not (task:has_from(1) and task:has_recipients(1)) then
            return false
        end
        local envfrom = task:get_from(1)
        local envrcpts = task:get_recipients(1)
        -- VERP only works for single recipient messages
        if table.getn(envrcpts) > 1 then return false end
        -- Get recipient and compute VERP address
        local rcpt = envrcpts[1].addr:lower()
        local verp = rcpt:gsub('@','=')
        -- Get the user portion of the envfrom
        local ef_user = envfrom[1].user:lower()
        -- See if the VERP representation of the recipient appears in it
        if ef_user:find(verp, 1, true)
           and not ef_user:find('+caf_=' .. verp, 1, true) -- Google Forwarding
           and not ef_user:find('^srs[01]=')               -- SRS
        then
            return true
        end
        return false
    end,
    score = 0.01,
    description = "Envelope From is a VERP address",
    group = "mailing_list"
}

rspamd_config.RCVD_TLS_ALL = {
    callback = function (task)
        local rcvds = task:get_header_full('Received')
        if not rcvds then return false end
        local count = 0
        local encrypted = 0
        for _, rcvd in ipairs(rcvds) do
            count = count + 1
            local r = rcvd['decoded']:lower()
            local by = r:match('^by%s+([^%s]+)') or r:match('%sby%s+([^%s]+)')
            local with = r:match('%swith%s+(e?smtps?a?)')
            if with and with:match('esmtps') then
                encrypted = encrypted + 1
            end
        end
        if (count > 0 and count == encrypted) then
            return true
        end
    end,
    score = 0.01,
    description = "All hops used encrypted transports",
    group = "encryption"
}

rspamd_config.MISSING_FROM = {
    callback = function(task)
      local from = task:get_header('From')
      if from == nil or from == '' then
        return true
      end
      return false
    end,
    score = 2.0,
    group = 'header',
    description = 'Missing From: header'
}