Active Directory

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Kerberos overview

  1. AS-REQ: Local timestamp, encrypted/signed with users hash is send to DC

  2. AS-REP: DC answers with Ticket Granting Ticket (TGT) (encrypted with krbtgt hash, so client cant decrypt it)

  3. TGS-REQ: Client sends TGT back & a Ticket Granting Service (TGS) request to DC in order to get a TGS-Ticket

  4. TGS-REP: DC sends TGS Ticket (encrypted/signed with target service NTLM hash)

  5. AP-REQ: Client presents TGS to Application Server (which knows its correct since it is encrypted with its service account or machine account hash)

Kerberos Attacks

  • Golden Ticket attacks TGS-REQ, validation is done on the DC only based on the TGT encryption, if we have a valid krbtgt hash it will accept everything inside it. (does not need the password, just the hash)

  • Silver Ticket forges a TGS-Ticket and presents it to the application server (needs the ntlm hash of a service account, so it can decrypt it), usually limited to a single target box

    • many services use the machine account as a service account

    • can be created for HOST, RPCSS, CIFS, WSMAN, ....

  • Kerberoast extracts a service hash from a TGS-Ticket (usually a machine account, but there are some services running as

    user accounts, which will have a SP Names associated - we want to prioritize these)

  • ASREP-Roast captures the AS-REQ in order to crack it (its encrypted with the users hash). This needs kerberos preauthentication disabled. In some cases we can disable it with the right acl conditions.

Kerberos Double Hop Problem

  • Can't log into application server and server then impersonates the same user to log into another box e.g. a db (only one hop allowed)



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