Adversaries may abuse a valid Kerberos ticket-granting ticket (TGT) or sniff network traffic to obtain a ticket-granting service (TGS) ticket that may be vulnerable to Brute Force.^[1],[2]

Service principal names (SPNs) are used to uniquely identify each instance of a Windows service. To enable authentication, Kerberos requires that SPNs be associated with at least one service logon account (an account specifically tasked with running a service^[3]).^{[4],[5],[6],[7]}

Adversaries possessing a valid Kerberos ticket-granting ticket (TGT) may request one or more Kerberos ticket-granting service (TGS) service tickets for any SPN from a domain controller (DC).^[1],[2] Portions of these tickets may be encrypted with the RC4 algorithm, meaning the Kerberos 5 TGS-REP etype 23 hash of the service account associated with the SPN is used as the private key and is thus vulnerable to offline Brute Force attacks that may expose plaintext credentials.^[2],[1],[7]

This same behavior could be executed using service tickets captured from network traffic.^[2]

Cracked hashes may enable Persistence, Privilege Escalation, and Lateral Movement via access to Valid Accounts.^[6]

References

1. EmpireProject. (2016, October 31). Invoke-Kerberoast.ps1. Retrieved March 22, 2018.
2. Metcalf, S. (2015, December 31). Cracking Kerberos TGS Tickets Using Kerberoast – Exploiting Kerberos to Compromise the Active Directory Domain. Retrieved March 22, 2018.
3. Bani, M. (2018, February 23). Detecting Kerberoasting activity using Azure Security Center. Retrieved March 23, 2018.
4. Microsoft. (n.d.). Service Principal Names. Retrieved March 22, 2018.
5. Microsoft. (2010, April 13). Service Principal Names (SPNs) SetSPN Syntax (Setspn.exe). Retrieved March 22, 2018.
6. Medin, T. (2014, November). Attacking Kerberos - Kicking the Guard Dog of Hades. Retrieved March 22, 2018.
7. Schroeder, W. (2016, November 1). Kerberoasting Without Mimikatz. Retrieved September 23, 2024.

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