MaxPatrol SIEM

Detects cyberincidents that undermine cyber resilience of a company

T1558.003: Kerberoasting

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.

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).

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). 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.

This same behavior could be executed using service tickets captured from network traffic.

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

Positive Technologies products that cover the technique

MaxPatrol SIEM knowledge base

active_directory_attacks: PT-CR-874: Kerberoasting: Request TGS tickets with certain types of encryption. This may allow an attacker to pick a password for the service account. After that, an attacker can use the attacked account to gain access to the system and increase privileges
active_directory_attacks: PT-CR-878: Subrule_Tickets_Requested: A request for session tickets to access services is detected

Detection

IDDS0026Data source and componentActive Directory: Active Directory Credential RequestDescription

Monitor for anomalous Kerberos activity, such as enabling 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]).

Mitigation

IDM1027NamePassword PoliciesDescription

Ensure strong password length (ideally 25+ characters) and complexity for service accounts and that these passwords periodically expire. Also consider using Group Managed Service Accounts or another third party product such as password vaulting.

IDM1041NameEncrypt Sensitive InformationDescription

Enable AES Kerberos encryption (or another stronger encryption algorithm), rather than RC4, where possible.

IDM1026NamePrivileged Account ManagementDescription

Limit service accounts to minimal required privileges, including membership in privileged groups such as Domain Administrators.