Presentation presented on Hack In Paris 2016

1. from zero to system
Nabeel ahmed & tom gilis
on full disk encrypted windows system

2. From zero to system
on full disk encrypted windows system
ABOUT US
๏ Nabeel Ahmed, Security Researcher
and Penetration Tester, Dimension
Data Belgium
๏ I love to break things =)
๏ @NabeelAhmedBE
๏ blog.nabeelahmed.com
๏ Tom Gilis, Security Consultant (and Team
Leader) at Dimension Data Belgium
๏More “boring” stuff like compliancy, … 
๏@tgilis
๏Co-organizer of BruCON
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3. From zero to system
on full disk encrypted windows system
Inspiration
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4. From zero to system
on full disk encrypted windows system
November 2015
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5. From zero to system
on full disk encrypted windows system
Ian haken
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๏ A new way to defeat FDE
๏ Rogue Domain Controller
๏ Poison Credential Cache
๏ Windows Security Feature bypass

6. From zero to system
on full disk encrypted windows system
Ms15-122
๏ Implements trust relationship before local cache is updated
๏ Works on Windows Vista, Windows 7, Windows 8.1, Windows 10, Windows Server 2008 up to
2012 (Windows XP, Windows Server 2003, …)
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7. From zero to system
on full disk encrypted windows system
Bitlocker
๏ TPM (Trusted Platform Module)
๏ Pre-boot PIN
๏ USB Key
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8. From zero to system
on full disk encrypted windows system
๏ TPM (Trusted Platform Module)
๏
๏
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Bitlocker

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on full disk encrypted windows system
Bitlocker tpm
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๏ BitLocker key is stored in TPM
๏ No user interaction when decrypting
the drive
๏ Windows login screen is the first and
only line of defense

10. From zero to system
on full disk encrypted windows system
Trust relationship?
๏ Computer account password is used for trust
๏ Randomly generated every 30 days
๏ 2 computer account passwords are stored
๏ Stored in
“HKLMSECURITYPolicySecrets$machine.ACC”
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11. From zero to system
on full disk encrypted windows system
Bypassing the patch
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12. From zero to system
on full disk encrypted windows system
Difference
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Legitimate DC
Rogue DC

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on full disk encrypted windows system
Ticket missing
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14. From zero to system
on full disk encrypted windows system
SPN
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SPNs are used to support mutual authentication
between a client application and a service. A service
principal name is associated with an account and an
account can have many service principal names.
– MSDN
SPNs are usually formatted as SERVICE/HOST, but
sometimes they also include a port like
SERVICE/HOST:PORT.

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on full disk encrypted windows system
Demo time
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on full disk encrypted windows system
Kerberos Password change
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?????????? EXP_PASS

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on full disk encrypted windows system
Kerberos Password change
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?????????? EXP_PASS
NEW_PASS

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on full disk encrypted windows system
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Conclusion
๏ Checks if a service ticket (T) has been received
BUT only validates AFTER the password change
๏ MS16-014 / CVE-2016-0049
๏ “Suggested workaround” disable local
password caching
๏ Patched on all supported Windows versions

19. From zero to system
on full disk encrypted windows system
Bluebox
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๏ Automated exploitation of MS15-122 and MS16-014
๏ Less than 1 minute
๏ Written in Python 
๏ Portable (Raspberry Pi)
๏ Kudos to Ian Haken (@ianhaken)
๏ https://github.com/JackOfMostTrades/bluebox

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on full disk encrypted windows system
WHAT’s NEXT ?
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๏ Extract any personal data
o Documents, emails, passwords..
๏ Requires admin privileges to :
o Retrieve BitLocker Recovery Key (or disable it)
o Install Malware
o Extract data from other users
o …

21. From zero to system
on full disk encrypted windows system
Trust relationship?
๏ Trust relationship is not always validated
๏ Working Active Directory set-up
๏ Any other Windows functionality missing trust validation?
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22. From zero to system
on full disk encrypted windows system
PRIVILEGE ESCALATION
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Will Group Policies work ?
๏ Works on all supported Windows versions
๏ No need for additional (vulnerable) software
๏ No specific configuration requirements

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on full disk encrypted windows system
Group Policies
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User Configuration Computer Configuration
During login (or on refresh) Before login (or on refresh)
User or
SYSTEM Privileges
SYSTEM Privileges
User account password Machine account password

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on full disk encrypted windows system
Group Policies
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User Configuration Computer Configuration
During login (or on refresh) Before login (or on refresh)
User or
SYSTEM Privileges
SYSTEM Privileges
User account password Machine account password

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on full disk encrypted windows system
Group policies
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on full disk encrypted windows system
EXAMPLE – CMD AS SYSTEM
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1. New Group Policy and assign it to the user account
2. Add the following configuration to the policy :
• Download file (e.g. NetCat.exe)
• Run NetCat as SYSTEM
• Connect to service as User
Screenshot Scheduled task GPO

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on full disk encrypted windows system
It works!?
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on full disk encrypted windows system
Why does it work?
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๏ Client can successfully authenticate against the DC using
his credentials
๏ All encrypted traffic remains intact (SMB,LDAP,RPC)
๏ Assumes that the user credentials are sufficient to
acknowledge trust relationship.
๏ Reported to Microsoft, who acknowledged the vulnerability
but ...

29. From zero to system
on full disk encrypted windows system
IS it NEW ?
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๏ Luke Jennings (MWR Labs) demonstrated how you can gain
SYSTEM access through MITM in March 2015
๏ MITM attack against legitimate GPO communication, resulting
two patches (MS15-011 and MS15-014)
๏ Jennings’ conclusion : “Even on Vista/2008 onwards, user
settings group policy can be exploited if you know a user’s
password to conduct a form of privilege escalation to gain
SYSTEM on domain members. Microsoft have shown no
intention thus far of providing a control to protect against this.”

30. From zero to system
on full disk encrypted windows system
WINDOWS 10 ?
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31. From zero to system
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WINDOWS 10 ?
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32. From zero to system
on full disk encrypted windows system
WIN 7 vs Win 10
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33. From zero to system
on full disk encrypted windows system
WIN 7 vs Win 10
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on full disk encrypted windows system
Relative ID
User SID
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S-1-5-21-124525095-708259637-1543119021-20937
Domain Security Identifier
Incremental
Uses Machine SID
when new domain is
created

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on full disk encrypted windows system
Setting the SID
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๏ Possibilities :
o Setting the Machine SID before the AD is created:
o Windows SysPrep – Generates new “random” SID
o Commercial tools exist
o Off-line edit the NTDS.DIT File
o SAMBA NT4 PDC to AD-DC
Lengthy, complex and prone to errors

36. From zero to system
on full disk encrypted windows system
mimikatz to the rescue
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Demo time
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on full disk encrypted windows system
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Conclusion
๏ First validates trust with computer account
๏ MS16-072 / CVE-2016-3223
๏ Took approx. 8 months to patch and then …

39. From zero to system
on full disk encrypted windows system
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40. From zero to system
on full disk encrypted windows system
Recovering original password
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๏ (convert .sys to .dmp)
๏ WinDbg
๏ Mimikatz (extract plaintext credentials)
๏ Only Windows 7 and below
Force
Hibernation
Bypass login
screen
Elevate
privileges
Extract
HIBERFIL.SYS
Reset Local
Password Cache

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on full disk encrypted windows system
timeline
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on full disk encrypted windows system
timeline
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43. From zero to system
on full disk encrypted windows system
Take aways
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๏ Trust relationships not always validated
๏ Don’t take physical security for granted
๏ Backwards compatibility makes patching very difficult
๏ Bypassing authentication and escalating privileges without a
single line of code
๏ Kudos to Ian Haken @ianhaken and Benjamin Delpy @gentilwiki
๏ Third time’s a charm?
o November 2015 (MS15-122)
o February 2016 (MS16-014)
o … July 2016  (MS16-???)
@nabeelahmedbe
blog.ahmednabeel.com
@tgilis