Windows.EventLogs.Kerbroasting

This Artifact will return all successful Kerberos TGS Ticket events for Service Accounts (SPN attribute) implemented with weak encryption. These tickets are vulnerable to brute force attack and this event is an indicator of a Kerbroasting attack.

Typical attacker methodology is to firstly request accounts in the domain with SPN attributes, then request an insecure TGS ticket for brute forcing. This attack is particularly effective as any domain credentials can be used to implement the attack and service accounts often have elevated privileges. Kerbroasting can be used for privilege escalation or persistence by adding a SPN attribute to an unexpected account.

Log Source: Windows Security Event Log (Domain Controllers). Event ID: 4769 Status: 0x0 (Audit Success) Ticket Encryption: 0x17 (RC4) Service Name: NOT krbtgt or NOT a system account (account name ends in $) TargetUserName: NOT a system account ($@)

Monitor and alert on unusual events with these conditions from an unexpected IP. Note: There are potential false positives so whitelist normal source IPs and manage risk of insecure ticket generation.

name: Windows.EventLogs.Kerbroasting
author: Matt Green - @mgreen27

description: |
  This Artifact will return all successful Kerberos TGS Ticket events for
  Service Accounts (SPN attribute) implemented with weak encryption. These
  tickets are vulnerable to brute force attack and this event is an indicator
  of a Kerbroasting attack.

  Typical attacker methodology is to firstly request accounts in the domain
  with SPN attributes, then request an insecure TGS ticket for brute forcing.
  This attack is particularly effective as any domain credentials can be used
  to implement the attack and service accounts often have elevated privileges.
  Kerbroasting can be used for privilege escalation or persistence by adding a
  SPN attribute to an unexpected account.

  Log Source: Windows Security Event Log (Domain Controllers).
  Event ID: 4769
  Status: 0x0 (Audit Success)
  Ticket Encryption: 0x17 (RC4)
  Service Name: NOT krbtgt or NOT a system account (account name ends in $)
  TargetUserName: NOT a system account (*$@*)

  Monitor and alert on unusual events with these conditions from an unexpected
  IP.
  Note: There are potential false positives so whitelist normal source IPs and
  manage risk of insecure ticket generation.

reference:
  - https://attack.mitre.org/techniques/T1208/
  - https://www.trustedsec.com/blog/art_of_kerberoast/

parameters:
  - name: EvtxGlob
    default: '%SystemRoot%\System32\winevt\logs\Security.evtx'
  - name: VSSAnalysisAge
    type: int
    default: 0
    description: |
      If larger than zero we analyze VSS within this many days
      ago. (e.g 7 will analyze all VSS within the last week).  Note
      that when using VSS analysis we have to use the ntfs accessor
      for everything which will be much slower.

sources:
  - query: |
      LET VSS_MAX_AGE_DAYS <= VSSAnalysisAge
      LET Accessor = if(condition=VSSAnalysisAge > 0, then="ntfs_vss", else="auto")

      -- expand provided glob into a list of paths on the file system (fs)
      LET fspaths = SELECT OSPath
        FROM glob(globs=expand(path=EvtxGlob))

      -- function returning IOC hits
      LET evtxsearch(PathList) = SELECT * FROM foreach(
            row=PathList,
            query={
                SELECT
                    timestamp(epoch=int(int=System.TimeCreated.SystemTime)) AS EventTime,
                    System.EventID.Value as EventID,
                    System.Computer as Computer,
                    EventData.ServiceName as ServiceName,
                    EventData.ServiceSid as ServiceSid,
                    EventData.TargetUserName as TargetUserName,
                    format(format="0x%x", args=EventData.Status) as Status,
                    EventData.TargetDomainName as TargetDomainName,
                    format(format="0x%x", args=EventData.TicketEncryptionType) as TicketEncryptionType,
                    format(format="0x%x", args=EventData.TicketOptions) as TicketOptions,
                    EventData.TransmittedServices as TransmittedServices,
                    EventData.IpAddress as IpAddress,
                    EventData.IpPort as IpPort,
                    OSPath
                FROM parse_evtx(filename=OSPath, accessor=Accessor)
                WHERE
                    System.EventID.Value = 4769
                    AND EventData.TicketEncryptionType = 23
                    AND EventData.Status = 0
                    AND NOT EventData.ServiceName =~ "krbtgt|\\$$"
                    AND NOT EventData.TargetUserName =~ "\\$@"
          })


        SELECT * FROM evtxsearch(PathList=fspaths)