Deploying Privileged Access Workstations (PAWs)

DEPLOYING PRIVILEGED ACCESS WORKSTATIONS (PAWS)

AS PART OF A STRATEGY TO LIMIT

CREDENTIAL THEFT AND LATERAL MOVEMENT

C:\whoami

•@blueteamer

•Financial Sector - 100 employees and 10 locations

•SMB = Lot of hats

•Network admin + Vendor Management + Sysadmin

+ Physical Security + Risk Assessment – wide range

•Love what I do

WHEN NOT COMPUTERING…

•Building stuff with my hands

•Pirate ship in backyard

•Homebrew

•Grilling/Smoking

ATTACK SCENARIO #1

•Non security conscious org

•Most users running as local admin

•Attack dumps local creds

•Local admin creds are the same on every PC

•Attacker moves laterally, dumps more creds

•Quick path to Domain Admin

ATTACK SCENARIO #2

•Somewhat security conscious org

•Most users running as standard

•Attacker needs to escalate privileges

•May abuse misconfigs or find creds on network

•Move laterally until escalation success & dump creds

•Rinse/Lather/Repeat until goal achieved

WHY PAWS?

•Scenarios not all encompassing

•Domain Admin may not be end goal

•Attacker tactics revolve around finding/using creds

•Main goal of PAWs – limit this exposure

• WINDOWS LOGON TYPES

• Interactive [2]

•Network [3] – No Reusable Credentials

• Net use

• SQL Windows

Authentication

• Powershell Remoting

• Remote Registry

• Other MMC Snap-ins

• WMI / WMIC

• Batch [4]

• Service [5]

• Unlock [7]

• Network Cleartext [8]

• New Credentials [9]

• Remote Interactive [10]

• Cached Interactive [11]

LOCAL SAM DATABASE

ACTIVE DIRECTORY DATABASE

•AKA – NTDS.dit

•Credentials for all user accounts in domain

•Read-only DCs by default don’t store privileged creds

•Mimikatz and WCE pull creds from here

•User logs on – LSASS caches creds for future use

•Can be hashes, Kerberos tickets, or plaintext

Prior to

Windows 8.1,

Server 2012 &

KB2871997

Changes with

Windows 8.1,

Server 2012 &

KB2871997

This GPO forces

computers to keep

tspkg creds in memory

and creates

these reg

values to do so

LSA SECRETS

•Data only accessible to SYSTEM process

•Credentials are encrypted and stored on disk

•Scheduled tasks

•Computer Account

•Service Accounts

LSA SECRETS

•Domain cached credentials – aka password verifiers

•Stored in salted hash format

•Can’t be passed in a Pass-the-Hash attack

•Can be dumped and brute forced

CREDENTIAL MANAGER

•Passwords entered manually via Control Panel applet

•Or when user tells Windows to remember password

•Remote Desktop, IE Autocomplete

•Encrypted with key derived from user’s password

•Any program running as that user can access

WINDOWS CREDENTIAL & AUTH ISSUES

•Pass-the-Hash Attacks

•NTLM hashes acquired from memory or SAM

•Can be used to authenticate just as Windows does

•Auth via NTLM protocols uses challenge/ response

•NTLMv1 – completely broken

• Attacker can recover hash if traffic can be capture on wire

•NTLMv2 – better but brute force still possible

•Both vulnerable to relay attacks – Use SMB Signing

•Kerberos – Pass-the-Ticket

•Dumped from one computer and loaded on another

•Tickets can be extended by presenting expired TGT

•Other Issues

•Golden/Silver Tickets, etc.

•Windows Access Tokens

•Not well known among defenders

•User logs on, system verifies password

• If password OK, access token is created

•Every process this user runs has copy of token

•Stored in memory, enable single sign-on

•Impersonation Tokens - Non-Interactive Logons

•Can be used to escalate privs, but only good locally

•Delegation Tokens - Interactive Logons

•Attacker can steal more privileged user's token

•Use it on any network accessible system

STEALING WINDOWS ACCESS TOKENS

•Incognito – Tool from Luke Jennings

•Presented at Defcon 15 in 2008

•Whitepaper – Security Implications of Windows Access

Tokens – A Penetration Tester’s Guide

https://labs.mwrinfosecurity.com/assets/142/original/mwri_security-implications-of-windows-access-

tokens_2008-04-14.pdf

WINDOWS CRED & AUTH ISSUES

•Cred theft – major issue for a long time

•Roadblocks to overcome

• IT Admins may not understand the risk

•Change is hard; usability > security

•No “patch” for these issues

•Light at the end of the tunnel

INTRODUCING PAWS

•Hardened admin workstations

•Designed to limit credential theft of privileged accounts

•Similar in theory to network segmentation

•Requires grouping systems and users by privilege level

https://technet.microsoft.com/en-us/windows-server-docs/security/securing-privileged-access/privileged-access-

workstations

ACTIVE DIRECTORY ADMINISTRATIVE TIER MODEL

•Tier 0 – Domain Admin & Domain Controllers

•Tier 1 – Member Server Admins & Member Servers

•Tier 2 – Workstation Admins & Workstations

LOGON RESTRICTIONS

TRADITIONAL SOLUTIONS – JUMP SERVERS

PAW PREREQUISITES

•Remove local admin as many users as possible

•If necessary, give users multiple accounts and/or segment

•Legacy software may not play well with UAC

• Look for workarounds

•Put pressure on vendors

PAW PREREQUISITES

•Break out separate member server admins, if necessary

•Limit number of Tier 0 admins

•Delegate privileges in AD

•If possible, segment each group of admins

•Ops Server Admins; Dev Server Admins; Network Admins

PHASES OF DEPLOYMENT

•1) - Immediate deployment for AD Admins

•2) - Extend PAWs to all users with admin rights over

mission critical applications

•Cloud services admins, member server admins

•3) - Advanced PAW Security

PAW DEPLOYMENT MODELS

•Dedicated Hardware

•Pros – Strongest security separation

•Cons – Additional desk space, weight, hardware cost

•Simultaneous Use

•Pros – Lower hardware cost, better user experience

•Cons – Single keyboard/mouse can cause unintentional errors

•Simultaneous Use

• “User” VM locally on hardened PAW host, or

•VDI, RDP – “User” VMs managed centrally in datacenter

accessed from hardened PAW

DEPLOY PAW ACTIVE DIRECTORY FRAMEWORK

•Create-PAWOUs.ps1

•Create the new OU structure in Active Directory

•Create-PAWGroups.ps1

•Create the new security groups in the appropriate OUs

•Set-PAWOUDelegation.ps1

•Assign permissions to the new OUs to the appropriate groups

NEW OUsUsers that are members of:

Domain Admins

Enterprise Admins

or equivalent

PAW COMPUTER ACCOUNT GPOs

•Empty all local groups

•Add PAW Maintenance & Administrator to local admin

•Grant “PAW Users” group local login access

•Block Inbound Network Traffic

•Permit security scanning, patch management, etc.

•Configure WSUS for PAW

PAW USER GPOs

•Block Internet Access for PAW Users

•Allow internal and other necessary browsing

•Restrict Administrators from logging onto lower tier hosts

• Local Policies\Users Rights Assignment\Deny logon on…

•As a service

•As a batch job

• Locally

PAW GPOS – DENY LOWER TIER LOGON

PAW SETUP – PHASE 1 (AD ADMINS)

•Consider supply chain and trust manufacturer and supplier

•Acquire & validate installation media and other tools

•Windows 10 Enterprise if possible

•Credential Guard & Device Guard

•Set unique, complex password for local admin

PAW SETUP – PHASE 1 (AD ADMINS)

•Connect PAW to network, join domain

•Move to Admin\Tier 0\Devices

•Install Windows Updates and any necessary admins tools

•Carefully consider risk for each tool installed

•Forward logs to SIEM

•Validate hardening GPOs

PAW SETUP – PHASE 2 (RESTRICTED ADMIN)

•Controversial RestrictedAdmin mode

• Leaves no reusable credentials

•Enabling it opens up Pass-the-Hash via RDP

•Weigh the Risk vs. Reward

PAW SETUP – PHASE 2 (RESTRICTED ADMIN)

Open up systems

to Pass-the-Hash

via RDP

Further limit

reusable creds

left on systems

Lock down RDP:only trusted hosts

PAW SETUP – PHASE 2

•RestrictedAdmin Mode

•Off by default; Enable on destination systems with regedit

•Mstsc.exe /RestrictedAdmin

•To Force RestrictedAdmin mode:

• Restrict Delegation of credential to remote servers – GPO

• Link to Admin Computer OUs in each tier

• Limitation - Connections made with computer account

•Move objects to appropriate OUs

•Tier 1 Users, Groups, Computer Accounts

•Also add users to Tier 1 Admins group

•Allows restricting login to lower tier devices

•Optional Step – Allow whitelisted Internet destinations

•Cloud Service Administration

•Remote vendor application support

•Tier 1 admins may need additional/different tools

•Weigh risks again

•Enable Credential Guard, if possible

•Virtualizes Windows services that manage credentials

•To isolate from running OS and attacker with admin rights

•Requirements:

•Windows 10 Enterprise x64

• Secure Boot Enabled

•VMs must be Hyper-V

•Builds on Phase 1; Not dependent Phase 2

•Multi-factor authentication – Smart cards

•Whitelisting – Device Guard / Applocker

•Protected Users Group

•Authentication Policies and Silos

PAW SETUP – PHASE 3 (MULTI-FACTOR)

•Windows 2FA solutions great control, but not magic bullet

•Limitations:

•Only enforced on interactive logons

•Forcing smart card logons ensures hash never changes

•Mitigate by script that toggles “Smart Card Required”

PAW SETUP – PHASE 3 (PROTECTED USERS)

•Most painless control to implement to limit cred exposure

•Most benefits when running 2012 R2 functional level

•Forces more secure Kerberos; tickets 4 hours instead of 10

•Users must re-authenticate when TGT expires

•Feature/Limitation - No local cached credentials

PAW SETUP – PHASE 3 (AUTH POLICIES & SILOS)

•Pair well with Protected Users group

•Requires 2012 R2 Functional Level

•Control where accounts can log on

•Which services they can authenticate to

•Set TGT settings

LESSONS LEARNED FROM MY DEPLOYMENT

•Windows 10 Enterprise Hyper-V is Awesome

•Dual monitors, audio & mic, copy+paste, separate vlans

•So many user accounts! The struggle is real

•Dramatic shift in day to day

•Sometimes “User Bill” doesn’t love “Security Bill”

•You can do it! Figure out system that works for you

LESSONS LEARNED FROM MY DEPLOYMENT

•Allow internal web browsing from admin host

•ProxyOverride GPO setting

•Scripting Hyper-V Virtual Switch config changes, etc.

PAW DEPLOYMENT PAIRS WILL WITH NETWORK SEGMENTATION

Site1 Site2

Site1_HR – 192.168.52.0/24

Site1_IT – 192.168.53.0/24

Site2_Legal – 192.168.60.0/24

Site2_HR – 192.168.62.0/24

Site2_IT – 192.168.63.0/24

Site3_HR – 192.168.72.0/24

Site3_IT – 192.168.73.0/24

Site1_Legal – 192.168.50.0/24

Site1_Accounting – 192.168.51.0/24Site2_Accounting – 192.168.61.0/24

Site3_Accounting – 192.168.71.0/24

Site3_Legal – 192.168.70.0/24

PAW DEPLOYMENT PAIRS WILL WITH NETWORK SEGMENTATION

Site1_Legal – 192.168.50.0/24

Site1_HR – 192.168.52.0/24

Site1_IT – 192.168.53.0/24

Site2_Legal – 192.168.60.0/24

Site2_HR – 192.168.62.0/24

Site2_IT – 192.168.63.0/24

Site3_Legal – 192.168.70.0/24

Site3_HR – 192.168.72.0/24

Site3_IT – 192.168.73.0/24

Internet

Cloud Remote

Support Service

NETWORK SEGMENTATION (LAYER3)

ACL MAPACL1 Site1_Legal

ACL2 Site1_Accounting

ACL3 Site1_HR

ACL4 Site1_IT

ACL5 Site2_Legal

ACL7 Site2_HR

ACL8 Site2_IT

ACL9 Site3_Legal

ACL11 Site3_HR

ACL12 Site3_IT

Site1 Site2

Site1_HR – 192.168.52.0/24

Site1_IT – 192.168.53.0/24

Site2_Legal – 192.168.60.0/24

Site2_HR – 192.168.62.0/24

Site2_IT – 192.168.63.0/24

Site3_HR – 192.168.72.0/24

Site3_IT – 192.168.73.0/24

ACL1ACL2

ACL4ACL8

ACL7ACL6ACL5

ACL11ACL10ACL9

Site1_Legal – 192.168.50.0/24

Site3_Legal – 192.168.70.0/24

Site1 Site2

Site1_HR – 192.168.52.0/24

Site1_IT – 192.168.53.0/24

Site2_Legal – 192.168.60.0/24

Site2_HR – 192.168.62.0/24

Site2_IT – 192.168.63.0/24

Site3_HR – 192.168.72.0/24

Site3_IT – 192.168.73.0/24

ACL1ACL2

ACL4ACL8

ACL7ACL6ACL5

ACL11ACL10ACL9

Site1_Legal – 192.168.50.0/24

Site3_Legal – 192.168.70.0/24

Site1_Switch

VLAN50 – Site1_Legal

Legal_User1 Legal_User2

Define VLAN Traffic

Define Allowed VLAN Traffic

Forward Allowed Traffic

Drop all other intra-VLAN traffic

Permit Everything Else

Apply Access List to VLAN 50

FURTHER LIMITING EXPOSURE TO CREDENTIAL THEFT AND LATERAL MOVEMENT

•Randomize local admin – Use LAPS or similar

•Windows Settings\Local Policies\User Rights Assignment

•Deny access to this computer from the network

•Deny log on through Terminal Services

• S-1-5-113: NT AUTHORITY\Local account

• S-1-5-114: NT AUTHORITY\Local account and member of Administrators group

FURTHER LIMITING EXPOSURE TO CREDENTIAL THEFT AND LATERAL MOVEMENT

•Disable LLMNR and Netbios

•Limit Service Account Privileges

•Use Managed Service Accounts

•Force NTLMv2

CLOSING

•Stop buying blinky boxes as a cure-all

•Take time to truly understand the risk

•Research and learn offensive techniques

•Find your weak points, build walls, set tripwires,

plug the holes the best you can

THANKS / PEOPLE TO FOLLOW

@curi0usJack

@TonikJDK

@harmj0y

@obscuresec

@passingthehash

@gentilkiwi

@hardwaterhacker

@HackerHurricane

@mattifestation

@mikepilkington

@PyroTek3

@scriptjunkie

• BrakeSec Podcast • Defensive Security Podcast

QUESTIONS/CONTACT

@blueteamer

http://blueteamer.blogspot.com/

Feel free to contact me with any questions

REFERENCES

• PAW Technet Article

• https://technet.microsoft.com/en-us/windows-server-docs/security/securing-privileged-access/privileged-access-workstations

• Security Implications of Windows Access Tokens – A Penetration Tester’s Guide

• https://labs.mwrinfosecurity.com/assets/142/original/mwri_security-implications-of-windows-access-tokens_2008-04-14.pdf

• Hello my name is Microsoft and I have a credential problem

• https://media.blackhat.com/us-13/US-13-Duckwall-Pass-the-Hash-WP.pdf

• Mitigating Service Account Credential Theft on Windows

• https://community.rapid7.com/docs/DOC-2881

• Pass-the-Hash Whitepapers

• https://www.microsoft.com/en-us/download/details.aspx?id=36036

• Abusing Kerberos Whitepaper

• https://www.blackhat.com/docs/us-14/materials/us-14-Duckwall-Abusing-Microsoft-Kerberos-Sorry-You-Guys-Don't-Get-It-wp.pdf

REFERENCES

• https://www.blackhat.com/docs/us-15/materials/us-15-Metcalf-Red-Vs-Blue-Modern-Active-Directory-Attacks-Detection-And-Protection.pdf

• https://www.scriptjunkie.us/2013/09/remote-desktop-and-die/

• http://www.irongeek.com/i.php?page=videos/bsidescleveland2016/101-

preventing-credential-theft-lateral-movement-after-initial-compromise-cameron-

• https://dirteam.com/sander/2013/07/18/security-thoughts-pass-the-hash-and-

other-credential-theft/

• https://logrhythm.com/blog/detecting-lateral-movement-from-pass-the-hash-attacks/

• https://technet.microsoft.com/en-us/security/dn920237.aspx

• https://www.blackhat.com/docs/us-15/materials/us-15-Moore-Defeating%20Pass-

the-Hash-Separation-Of-Powers-wp.pdf

• https://www.crowdstrike.com/blog/mitigating-pass-hash-pth/

• https://channel9.msdn.com/Blogs/Taste-of-Premier/Proactively-Secure-your-IT-

Environment-from-Credential-Theft-with-POP-SLAM

• https://channel9.msdn.com/Events/TechEd/NorthAmerica/2013/ATC-B210

• https://www.secureworks.com/blog/targeted-credential-theft

• http://www.derekseaman.com/2013/06/teched-pass-the-hash-preventing-lateral-

movement-atc-b210.html

• https://channel9.msdn.com/Events/Blue-Hat-Security-Briefings/BlueHat-Security-

Briefings-Fall-2012-Sessions/BH1208

• https://channel9.msdn.com/events/teched/northamerica/2014/dcim-b359#fbid=

• https://technet.microsoft.com/library/dn408187.aspx

• https://www.trustedsec.com/april-2015/dumping-wdigest-creds-with-meterpreter-

mimikatzkiwi-in-windows-8-1/

• https://www.schneier.com/blog/archives/2016/05/credential_stea.html

• https://technet.microsoft.com/en-us/library/dn466518(v=ws.11).aspx

• https://blogs.technet.microsoft.com/askpfeplat/2016/04/04/reading-the-fine-print-

on-the-protected-users-group/

• https://blogs.technet.microsoft.com/kfalde/2014/11/01/kb2871997-and-wdigest-

part-1/

• http://passing-the-hash.blogspot.com/2014/03/guest-post-lets-talk-about-pass-

hash-by.html

REFERENCES

• https://dfir-blog.com/2015/11/08/protecting-windows-networks-defeating-pass-

the-hash/

• https://dirteam.com/sander/2014/11/25/ten-things-you-need-to-be-aware-of-

before-using-the-protected-users-group/

• https://adsecurity.org/?p=1667

• https://digital-forensics.sans.org/blog/2012/03/21/protecting-privileged-domain-

accounts-access-tokens

• https://technet.microsoft.com/en-us/security/dn920237.aspx

• https://technet.microsoft.com/en-us/magazine/2006.08.securitywatch.aspx

• https://adsecurity.org/?p=1684

• https://blogs.technet.microsoft.com/canitpro/2016/06/23/step-by-step-enabling-

restricted-admin-mode-for-remote-desktop-connections/

• https://labs.portcullis.co.uk/blog/new-restricted-admin-feature-of-rdp-8-1-allows-

pass-the-hash/

accounts-restricted-admin-and-protected-users

• http://www.geektime.com/2014/04/02/remote-desktops-restricted-admin-is-the-

cure-worse-than-the-disease/

• http://www.exploit-monday.com/2016/09/introduction-to-windows-device-

guard.html

• https://dfir-blog.com/2015/11/24/protecting-windows-networks-dealing-with-

credential-theft/comment-page-1/#comment-527

• http://www.rsmusconsultingpros.com/prevent-token-impersonation/

• https://clymb3r.wordpress.com/2013/06/13/using-powershell-to-copy-ntds-dit-

registry-hives-bypass-sacls-dacls-file-locks/

• https://dirteam.com/sander/2014/12/23/new-features-in-active-directory-domain-

services-in-windows-server-2012-r2-part-3-authentication-policies-and-

authentication-policy-silos/

• https://technet.microsoft.com/windows-server-docs/identity/ad-ds/manage/how-to-

configure-protected-accounts

accounts-restricted-admin-and-protected-users

• https://technet.microsoft.com/en-us/itpro/windows/keep-secure/credential-guard

• https://adsecurity.org/wp-content/uploads/2016/08/DEFCON24-2016-Metcalf-

BeyondTheMCSE-RedTeamingActiveDirectory.pdf

Deploying Privileged Access Workstations (PAWs)

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