Suspicious Kerberos Service Ticket Request

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Description

As part of the sAMAccountName Spoofing (CVE-2021-42278) and Domain Controller Impersonation (CVE-2021-42287) exploitation chain, adversaries will request and obtain a Kerberos Service Ticket (TGS) with a domain controller computer account as the Service Name. This Service Ticket can be then used to take control of the domain controller on the final part of the attack. This analytic leverages Event Id 4769, A Kerberos service ticket was requested, to identify an unusual TGS request where the Account_Name requesting the ticket matches the Service_Name field. This behavior could represent an exploitation attempt of CVE-2021-42278 and CVE-2021-42287 for privilege escalation.

• Type: TTP

• Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

• Last Updated: 2021-12-20
• Author: Mauricio Velazco, Splunk
• ID: 8b1297bc-6204-11ec-b7c4-acde48001122

Annotations

ATT&CK

ATT&CK

ID	Technique	Tactic
T1078	Valid Accounts	Defense Evasion, Persistence, Privilege Escalation, Initial Access

T1078.002

Domain Accounts

Defense Evasion, Persistence, Privilege Escalation, Initial Access

Kill Chain Phase

• Exploitation
• Installation
• Delivery

NIST

• DE.CM

CIS20

• CIS 10

CVE

ID	Summary	CVSS
CVE-2021-42287	Active Directory Domain Services Elevation of Privilege Vulnerability This CVE ID is unique from CVE-2021-42278, CVE-2021-42282, CVE-2021-42291.	6.5
CVE-2021-42278	Active Directory Domain Services Elevation of Privilege Vulnerability This CVE ID is unique from CVE-2021-42282, CVE-2021-42287, CVE-2021-42291.	6.5

Search

 `wineventlog_security` EventCode=4769 
| eval isSuspicious = if(lower(Service_Name) = lower(mvindex(split(Account_Name,"@"),0)+"$"),1,0) 
| where isSuspicious = 1 
| rename ComputerName as dest
| rename Account_Name as user  
| table _time, dest, Client_Address, Account_Name, Service_Name, Failure_Code, isSuspicious 
| `suspicious_kerberos_service_ticket_request_filter`

Macros

The SPL above uses the following Macros:

• wineventlog_security

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

Required fields

List of fields required to use this analytic.

• _time
• EventCode
• Service_Name
• Account_Name
• Client_Address
• Failure_Code

How To Implement

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.

Known False Positives

We have tested this detection logic with ~2 million 4769 events and did not identify false positives. However, they may be possible in certain environments. Filter as needed.

Associated Analytic Story

• sAMAccountName Spoofing and Domain Controller Impersonation
• Active Directory Kerberos Attacks
• Active Directory Privilege Escalation

RBA

Risk Score	Impact	Confidence	Message
60.0	100	60	A suspicious Kerberos Service Ticket was requested by $user$ on host $dest$

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

Reference

• https://exploit.ph/cve-2021-42287-cve-2021-42278-weaponisation.html
• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-42278
• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-42287
• https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-sfu/02636893-7a1f-4357-af9a-b672e3e3de13

Test Dataset

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

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