Detection: Kerberoasting spn request with RC4 encryption

Updated Date: 2024-10-16 ID: 5cc67381-44fa-4111-8a37-7a230943f027 Author: Jose Hernandez, Patrick Bareiss, Mauricio Velazco, Dean Luxton, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects potential Kerberoasting attacks by identifying Kerberos service ticket requests with RC4 encryption through Event ID 4769. It leverages specific Ticket_Options values commonly used by Kerberoasting tools. This activity is significant as Kerberoasting allows attackers to request service tickets for domain accounts, typically service accounts, and crack them offline to gain privileged access. If confirmed malicious, this could lead to unauthorized access, privilege escalation, and further compromise of the Active Directory environment.

Search

1`wineventlog_security` EventCode=4769 ServiceName!="*$" (TicketOptions=0x40810000 OR TicketOptions=0x40800000 OR TicketOptions=0x40810010) TicketEncryptionType=0x17 
2| stats count min(_time) as firstTime max(_time) as lastTime by Computer, user, service_id, service, TicketEncryptionType, TicketOptions 
3| rename Computer as dest 
4| `security_content_ctime(lastTime)` 
5| `security_content_ctime(firstTime)` 
6| `kerberoasting_spn_request_with_rc4_encryption_filter`

Data Source

Name	Platform	Sourcetype	Source
Windows Event Log Security 4769	Windows	`'xmlwineventlog'`	`'XmlWinEventLog:Security'`

Macros Used

Name	Value
security_content_ctime	`convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)`
kerberoasting_spn_request_with_rc4_encryption_filter	`search *`

kerberoasting_spn_request_with_rc4_encryption_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1558	Steal or Forge Kerberos Tickets	Credential Access
T1558.003	Kerberoasting	Credential Access

KillChainPhase.EXPLOITAITON

NistCategory.DE_CM

Cis18Value.CIS_10

FIN7

Indrik Spider

Wizard Spider

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Notable	Yes
Rule Title	`%name%`
Rule Description	`%description%`
Notable Event Fields	user, dest
Creates Risk Event	True

This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

To successfully implement this search, you need to be ingesting Domain Controller and Kerberos events. The Advanced Security Audit policy setting Audit Kerberos Authentication Service within Account Logon needs to be enabled. Whithin environments where this type of communication is common, consider dropping the risk score and add throttling based on the user and service_id for 30 days. This will allow RBA to alert when there is an anomalous spike of these kerberoastable SPN requests within a short period of time.

Known False Positives

Older systems that support kerberos RC4 by default like NetApp may generate false positives. Filter as needed

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
User $user$ requested a service ticket for SPN $service_id$ with RC4 encryption	72	90	80

The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`XmlWinEventLog:Security`	`XmlWinEventLog`
Integration	✅ Passing	Dataset	`XmlWinEventLog:Security`	`XmlWinEventLog`

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 7