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Windows Domains Part 2

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An in-depth walkthrough of authentication in a Windows Domain covering NTLM and Kerberos.

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Windows Domains Part 2

  1. 1. Domain Hacking and Pivoting March 21st 2018
  2. 2. Get in touch with us Mailing List - Sign in and check “Add to Mailing List” Website - csg.utdallas.edu Slack - #csg on ecsutd.slack.com Email - utdcsg@gmail.com
  3. 3. Announcements Lab Hangouts - ECSS 4.619 - Every Thursday at 4 PM State Farm CTF
  4. 4. Domain Hacking & Pivoting 1. Domain Concept Refresher a. What is a domain? b. Single sign on 2. Authentication a. NTLM b. Kerberos c. Differences 3. Attacking Authentication: Pass The Hash a. NTLM b. Kerberos c. Demo 4. Defenses a. Solid plan A b. Solid plan B thru ... c. Harden, harden, harden 5. Future Technologies a. Windows ATP b. Credential Guard
  5. 5. Domains
  6. 6. What is a domain? ● A bunch of computers connected together in a hierarchical structure ○ Domain Controller (DC) - Tells people the rules and handles authentication ○ Organizational Units (OUs) - Logically group things together ○ Group Policy Objects (GPOs) - Apply policies to things on the domain ○ Other stuff ■ Users that need access to network resources ■ Servers / workstations / everything else that makes up those network resources
  7. 7. What is a domain? http://www.conceptdraw.com/examples/active-directory-network
  8. 8. What is a domain? ● Analogy: an army ○ Network is the military base. ○ Domain is all the stuff on the base. ■ Troops, supplies, vehicles, etc. ○ DC is the top dog giving orders. ○ OUs to define different branches. ○ GPOs are the rules / orders to give everyone
  9. 9. Why do we care? ● Why do I want my company to have a domain? ○ For a similar reason to why you want your military to have an organized army and not just a bunch of dudes with rifles ○ Organization is good ○ Not all users are created equal ● So why do I, as an attacker, want to get on someone’s domain? ○ Go back to that analogy. ■ You become trusted. ■ You wanna be the top dog.
  10. 10. Single Sign-On ● Important concept with big implications on domain security! ● Make a user give credentials any time they access any network resource? ○ They don’t like that. ○ Also it’s slow; hinders productivity ● Solution: single sign-on! Only sign on once, and you can use any of the things that you’re authorized to use without signing on again, yay! ● Implementation ○ User logs on with credentials. Credentials get hashed. ○ Hash gets stored somewhere in memory on their computer. ○ Authenticate with the hash of the credentials rather than the credentials themselves, so you don’t have to store cleartext credentials or send them over the wire. ○ The result? Hashes get left around… usually.
  11. 11. Authentication
  12. 12. NTLM ● User enters credentials. They get hashed. ● Give hash to DC. DC authenticates user. ● User logs on. Hash gets stored on their computer. ● When they try to use network resources, they give that hash to the DC, DC makes sure they’re allowed to use that resource, grants access if so. ● Another analogy ○ There’s a toybox of network resources ○ DC is the toybox’s bouncer. ○ User gives DC their hash, they make sure user is on the list, then lets him play with that toy
  13. 13. Kerberos ● A bit more complicated than NTLM. ● All about the tickets. ○ Wanna talk to someone? Well, you need a valid Kerberos ticket. ● Where do I get these tickets? ● Kerberos server ○ Has two parts: Authentication Server (AS) and Ticket Granting Server (TGS) ○ Two types of tickets ■ Ticket Granting Ticket (TGT) - Ticket that lets you get Service Tickets ■ Service Ticket (ST) - Ticket that lets you use particular services
  14. 14. Kerberos ● User uses credentials at AS to get TGT ● User takes TGT to TGS to get TSs ● TSs let you use services ● Tickets are stored on user’s computer, but they expire after a while ● Visualization
  15. 15. More Sophisticated Diagram Source: Oracle Help Center
  16. 16. Why Kerberos is better than NTLM Kerberos ● Supports stronger encryption algorithms ● Less load on DC (infrequently authenticate with TGT) ● Actively developed ● Critical data (tickets) are (generally) valid for a few days ● Supports both user-to-server authentication and server-to-user authentication ● Is open source NTLM ● Uses weaker encryption algorithms ● More load on DC (authenticate with DC every time) ● No more development - MS is moving toward Kerberos ● Critical data (NTLM hashes) are valid until user changes password ● Only user-to-server authentication ● Is filthy proprietary software
  17. 17. Attacking Authentication: Pass The Hash
  18. 18. NTLM ● Logging into a computer on the domain stores your NTLM hash on that computer (most of the time*) ● If that computer gets compromised, HackerMan can grab any stored hashes, which can be used to authenticate against other parts of the domain as previously-logged-in users *”Network” login sessions usually don’t leave a hash (RDP being a notable exception). Every other type of session does. There are nine session types. https://www.ultimatewindowssecurity.com/securitylog/encyclopedia/event.aspx?eventI D=4624
  19. 19. NTLM ● If HackerMan happens to find a domain admin hash -> GG ● If not, use the best credentials you can, authenticate against other machines on the domain, compromise and grab even more hashes ○ Gradually escalate privileges, pivoting around the domain on to different machines as different users ● Demo It’s also worth mentioning that older versions of NTLM use very weak encryption that is trivial to crack
  20. 20. Kerberos Saves The Day? ● Gee, NTLM sure sounds bad. It’s a good thing modern Windows OSes use Kerberos by default! That means I’m safe from Pass The Hash, right? ● No. ● In the majority of networks, NTLM functions alongside Kerberos, for the sake of backward compatibility with a bunch of stuff. ● You can specifically disable all NTLM. This takes some kerjiggering, and can restrict some functionality, depending on what services you need on your domain. ● But if I do that, then am I safe?
  21. 21. Kerberos Saves The Day? ● Still, no. ● Tickets get stored locally, just like an NTLM hash. ● Kerberos is NOT meant to protect against Pass the Hash attacks. ● Only slight protection from PtH: tickets are not valid for as long as NTLM hashes are ● But still, lift someone’s TGT and you can request any services they have access to. ● “Pass the Ticket” attack. Basically a rebranded Pass the Hash. ● Open source tools already exist to do this.
  22. 22. Defenses
  23. 23. Solid Plan A ● Remember all the other security talks we’ve given this semester to keep attackers off your network ○ Keep patches up to date ○ Double check your configurations ○ Incorporate employees into your security team to defend against social engineering attacks ● But that isn’t enough.
  24. 24. Solid Plans B And Beyond ● Defenders should assume an attacker should get on their network ● Strict focus on boundary defenses has failed corporations repeatedly ● Harden your domain ○ Don’t leave admin hashes laying around ■ Make them manage computers via network logins, when possible ○ Fine tune privileges ■ Be granular when deciding who should be able to do what ■ Does the IT intern really need omega superadmin privileges? ○ Isolate critical components ■ Does omega superadmin really need an email address?
  25. 25. Future Technologies ● Windows Advanced Threat Protection (ATP) ○ https://www.youtube.com/watch?v=2HNuzUuVyv0 ● Credential Guard

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