Steal or Forge Kerberos Tickets
Sub-techniques (4)
Adversaries may attempt to subvert Kerberos authentication by stealing or forging Kerberos tickets to enable Pass the Ticket. Kerberos is an authentication protocol widely used in modern Windows domain environments. In Kerberos environments, referred to as “realms”, there are three basic participants: client, service, and Key Distribution Center (KDC).(Citation: ADSecurity Kerberos Ring Decoder) Clients request access to a service and through the exchange of Kerberos tickets, originating from KDC, they are granted access after having successfully authenticated. The KDC is responsible for both authentication and ticket granting. Adversaries may attempt to abuse Kerberos by stealing tickets or forging tickets to enable unauthorized access.
On Windows, the built-in klist utility can be used to list and analyze cached Kerberos tickets.(Citation: Microsoft Klist)
Linux systems on Active Directory domains store Kerberos credentials locally in the credential cache file referred to as the "ccache". The credentials are stored in the ccache file while they remain valid and generally while a user's session lasts.(Citation: MIT ccache) On modern Redhat Enterprise Linux systems, and derivative distributions, the System Security Services Daemon (SSSD) handles Kerberos tickets. By default SSSD maintains a copy of the ticket database that can be found in /var/lib/sss/secrets/secrets.ldb as well as the corresponding key located in /var/lib/sss/secrets/.secrets.mkey. Both files require root access to read. If an adversary is able to access the database and key, the credential cache Kerberos blob can be extracted and converted into a usable Kerberos ccache file that adversaries may use for Pass the Ticket. The ccache file may also be converted into a Windows format using tools such as Kekeo.(Citation: Linux Kerberos Tickets)(Citation: Brining MimiKatz to Unix)(Citation: Kekeo)
Kerberos tickets on macOS are stored in a standard ccache format, similar to Linux. By default, access to these ccache entries is federated through the KCM daemon process via the Mach RPC protocol, which uses the caller's environment to determine access. The storage location for these ccache entries is influenced by the /etc/krb5.conf configuration file and the KRB5CCNAME environment variable which can specify to save them to disk or keep them protected via the KCM daemon. Users can interact with ticket storage using kinit, klist, ktutil, and kcc built-in binaries or via Apple's native Kerberos framework. Adversaries can use open source tools to interact with the ccache files directly or to use the Kerberos framework to call lower-level APIs for extracting the user's TGT or Service Tickets.(Citation: SpectorOps Bifrost Kerberos macOS 2019)(Citation: macOS kerberos framework MIT)
Mitigations |
|
| Mitigation | Description |
|---|---|
| Active Directory Configuration |
Configure Active Directory to prevent use of certain techniques; use SID Filtering, etc. |
| Encrypt Sensitive Information |
Protect sensitive information with strong encryption. |
| Password Policies |
Set and enforce secure password policies for accounts. |
| Privileged Account Management |
Manage the creation, modification, use, and permissions associated to privileged accounts, including SYSTEM and root. |
Detection
Monitor for anomalous Kerberos activity, such as malformed or blank fields in Windows logon/logoff events (Event ID 4624, 4672, 4634), RC4 encryption within ticket granting tickets (TGTs), and ticket granting service (TGS) requests without preceding TGT requests.(Citation: ADSecurity Detecting Forged Tickets)(Citation: Stealthbits Detect PtT 2019)(Citation: CERT-EU Golden Ticket Protection)
Monitor the lifetime of TGT tickets for values that differ from the default domain duration.(Citation: Microsoft Kerberos Golden Ticket)
Monitor for indications of Pass the Ticket being used to move laterally.
Enable Audit Kerberos Service Ticket Operations to log Kerberos TGS service ticket requests. Particularly investigate irregular patterns of activity (ex: accounts making numerous requests, Event ID 4769, within a small time frame, especially if they also request RC4 encryption [Type 0x17]).(Citation: Microsoft Detecting Kerberoasting Feb 2018) (Citation: AdSecurity Cracking Kerberos Dec 2015)
Monitor for unexpected processes interacting with lsass.exe.(Citation: Medium Detecting Attempts to Steal Passwords from Memory) Common credential dumpers such as Mimikatz access the LSA Subsystem Service (LSASS) process by opening the process, locating the LSA secrets key, and decrypting the sections in memory where credential details, including Kerberos tickets, are stored.
Monitor for unusual processes accessing secrets.ldb and .secrets.mkey located in /var/lib/sss/secrets/.
References
- French, D. (2018, October 2). Detecting Attempts to Steal Passwords from Memory. Retrieved October 11, 2019.
- Metcalf, S. (2015, December 31). Cracking Kerberos TGS Tickets Using Kerberoast – Exploiting Kerberos to Compromise the Active Directory Domain. Retrieved March 22, 2018.
- Bani, M. (2018, February 23). Detecting Kerberoasting activity using Azure Security Center. Retrieved March 23, 2018.
- Microsoft. (2015, March 24). Kerberos Golden Ticket Check (Updated). Retrieved February 27, 2020.
- Abolins, D., Boldea, C., Socha, K., Soria-Machado, M. (2016, April 26). Kerberos Golden Ticket Protection. Retrieved July 13, 2017.
- Jeff Warren. (2019, February 19). How to Detect Pass-the-Ticket Attacks. Retrieved February 27, 2020.
- Metcalf, S. (2015, May 03). Detecting Forged Kerberos Ticket (Golden Ticket & Silver Ticket) Use in Active Directory. Retrieved December 23, 2015.
- Massachusetts Institute of Technology. (2007, October 27). Kerberos for Macintosh Preferences Documentation. Retrieved October 6, 2021.
- Cody Thomas. (2019, November 14). When Kirbi walks the Bifrost. Retrieved October 6, 2021.
- Benjamin Delpy. (n.d.). Kekeo. Retrieved October 4, 2021.
- Tim Wadhwa-Brown. (2018, November). Where 2 worlds collide Bringing Mimikatz et al to UNIX. Retrieved October 13, 2021.
- Trevor Haskell. (2020, April 1). Kerberos Tickets on Linux Red Teams. Retrieved October 4, 2021.
- Massachusetts Institute of Technology. (n.d.). MIT Kerberos Documentation: Credential Cache. Retrieved October 4, 2021.
- Microsoft. (2021, March 3). klist. Retrieved October 14, 2021.
- Sean Metcalf. (2014, September 12). Kerberos, Active Directory’s Secret Decoder Ring. Retrieved February 27, 2020.
- UCF. (n.d.). The password for the krbtgt account on a domain must be reset at least every 180 days. Retrieved November 5, 2020.
Связанные риски
Каталоги
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