Deploying privileged access workstations (PAWs) is part of a strategy to limit credential theft and lateral movement in an organization's network. PAWs are hardened administrative workstations designed to isolate privileged accounts and limit the exposure of credentials. An effective PAW strategy involves deploying dedicated hardware for administrators, applying security group policies and logon restrictions, and implementing additional controls like multi-factor authentication and device whitelisting.
7. HOW TO THINK LIKE AN ATTACKER?
•DSU is a good start
•Learn from Pros - @Twitter is awesome
•Embrace the infosec community
•OffensiveSecurityTraining++
8. 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
9. 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
10. 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
11. • 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]
17. LSA SECRETS
•Data only accessible to SYSTEM process
•Credentials are encrypted and stored on disk
•Scheduled tasks
•Computer Account
•Service Accounts
18. 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
19. 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
20. WINDOWS CREDENTIAL & AUTH ISSUES
•Pass-the-Hash Attacks
•NTLM hashes acquired from memory or SAM
•Can be used to authenticate just as Windows does
21. WINDOWS CREDENTIAL & AUTH ISSUES
•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
22. WINDOWS CREDENTIAL & AUTH ISSUES
•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.
23. WINDOWS CREDENTIAL & AUTH ISSUES
•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
24. WINDOWS CREDENTIAL & AUTH ISSUES
•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
27. 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
28. 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
29. 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
30. ACTIVE DIRECTORY ADMINISTRATIVE TIER
MODEL
•Tier 0 – Domain Admin & Domain Controllers
•Tier 1 – Member Server Admins & Member Servers
•Tier 2 – Workstation Admins & Workstations
33. 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
34. 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
35. 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
36. 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
37. PAW DEPLOYMENT MODELS
•Simultaneous Use
•“User” VM locally on hardened PAW host, or
•VDI, RDP – “User” VMs managed centrally in datacenter
accessed from hardened PAW
39. 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
40. NEW OUs
Users that are members of:
Domain Admins
Enterprise Admins
or equivalent
41. PAW HARDENING - COMPUTER 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
42. PAW HARDENING - USER GPOs
•Block Internet Access for PAW Users
•Allow internal and other necessary browsing
•Restrict Administrators from logging onto lower tier hosts
•Local PoliciesUsers Rights AssignmentDeny logon on…
•As a service
•As a batch job
•Locally
44. PAW SETUP – PHASE 1 (AD ADMINS)
•Acquire & validate installation media and other tools
•Windows 10 Enterprise if possible
•Credential Guard & Device Guard
•Set unique, complex password for local admin
45. PAW SETUP – PHASE 1 (AD ADMINS)
•Connect PAW to network, join domain
•Move to AdminTier 0Devices
•Install Windows Updates and any necessary admins tools
•Carefully consider risk for each tool installed
•Forward logs to SIEM
•Validate hardening GPOs
46. RESTRICTED ADMIN MODE
•Controversial RestrictedAdmin mode
•Leaves no reusable credentials
•Enabling it opens up Pass-the-Hash via RDP
•Weigh the Risk vs. Reward
47. RESTRICTED ADMIN MODE
Open up systems
to Pass-the-Hash
via RDP
Further limit
reusable creds
left on systems
vs.
Lock down RDP:
only trusted hosts
48. RESTRICTED ADMIN MODE
•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
49. REMOTE CREDENTIAL GUARD
•Same regedit as Restricted Admin mode to enable
•Mstsc.exe /remoteGuard
•Remote computer must be running Windows 10 - 1607 or
Windows Server 2016
•Limitation - signed on credentials only
•Benefit - Allows Multi-hop from the remote desktop
50. CREDENTIAL GUARD
•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
•TPM & CPU Virtualization ext.
54. PAW SETUP – PHASE 3
•Builds on Phase 1; Not dependent Phase 2
•Multi-factor authentication – Smart cards
•Whitelisting – Device Guard / Applocker
•Protected Users Group
•Authentication Policies and Silos
55. 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”
56. 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
57. 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
58. 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
59. FURTHER LIMITING EXPOSURE TO CREDENTIAL
THEFT AND LATERAL MOVEMENT
•Randomize local admin – Use LAPS or similar
61. 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
64. 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
