Detect Kerberoasting in Google Chronicle
Adversaries may abuse a valid Kerberos ticket-granting ticket (TGT) to request Kerberos ticket-granting service (TGS) tickets for any service principal name (SPN) registered in Active Directory. Portions of these tickets encrypted with RC4 (etype 0x17) use the service account's NTLM hash as the private key, making them vulnerable to offline brute force attacks using tools like Hashcat or John the Ripper. Cracked credentials enable persistence, privilege escalation, and lateral movement via valid domain accounts. Common tooling includes Rubeus, Invoke-Kerberoast (PowerSploit/Empire), Impacket GetUserSPNs.py, SILENTTRINITY, and Brute Ratel C4. Confirmed threat actor usage includes Wizard Spider (Ryuk ransomware campaigns), FIN7, and Indrik Spider.
MITRE ATT&CK
- Tactic
- Credential Access
- Technique
- T1558 Steal or Forge Kerberos Tickets
- Sub-technique
- T1558.003 Kerberoasting
- Canonical reference
- https://attack.mitre.org/techniques/T1558/003/
YARA-L Detection Query
rule t1558_003_kerberoasting_rc4_tgs_bulk {
meta:
author = "Detection Engineer"
description = "Detects Kerberoasting — bulk RC4-encrypted TGS requests (Event 4769, etype 0x17) indicating automated SPN enumeration"
mitre_attack_tactic = "Credential Access"
mitre_attack_technique = "T1558.003"
severity = "High"
reference = "https://attack.mitre.org/techniques/T1558/003/"
events:
$e.metadata.product_event_type = "4769"
not re.regex($e.principal.user.userid, `\$$`)
not re.regex($e.target.resource.name, `\$$`)
$e.target.resource.name != "krbtgt"
$e.additional.fields["TicketEncryptionType"] = "0x17"
$e.principal.user.userid = $user
$e.principal.ip = $ip
$e.target.resource.name = $spn
match:
$user, $ip over 1h
outcome:
$unique_spn_count = count_distinct($spn)
$tgs_request_count = count($e)
$alert_priority = if($unique_spn_count >= 20, "Critical",
if($unique_spn_count >= 5, "High", "Medium"))
$is_bulk_kerberoast = ($unique_spn_count >= 5)
condition:
#e >= 5
}Chronicle YARA-L 2.0 rule detecting Kerberoasting via bulk RC4-encrypted Kerberos TGS ticket requests. Matches Windows Security Event 4769 with etype 0x17, excludes machine accounts (userid or resource name ending with $) and krbtgt service tickets. Fires when 5 or more qualifying TGS requests originate from the same user and source IP within a 1-hour window. The TicketEncryptionType field is accessed via UDM additional.fields — verify the key name matches your Chronicle Windows Security Event Log parser configuration, as some parsers may map this field differently.
Data Sources
Required Tables
False Positives & Tuning
- Environments where AES-only Kerberos has not been enforced via Group Policy (msDS-SupportedEncryptionTypes) will produce 4769/RC4 events for all service authentication, generating significant false positive volume — the count threshold of 5+ unique SPNs helps focus on anomalous bulk requests
- Security assessment tools performing SPN enumeration or Kerberos compatibility checks (e.g. Kerbrute in enumerate mode, BloodHound collection runs using Kerberos auth) during authorized penetration tests — verify against change management calendar
- Application servers acting as Kerberos constrained delegation proxies that request service tickets on behalf of many frontend users, resulting in high SPN request counts attributed to the delegation account's source IP
Other platforms for T1558.003
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Invoke-Kerberoast via PowerSploit — Bulk Hash Extraction
Expected signal: Domain Controller Security Event ID 4769 for each SPN enumerated with TicketEncryptionType=0x17. Sysmon Event ID 1 on source host: powershell.exe with 'Invoke-Kerberoast' in CommandLine. Sysmon Event ID 3: TCP connection to DC on port 88 (Kerberos). PowerShell ScriptBlock Event ID 4104 with full Invoke-Kerberoast script content (deobfuscated). Sysmon Event ID 11: file creation for kerberoast_hashes.txt.
- Test 2Rubeus Kerberoast — All Roastable Accounts
Expected signal: Domain Controller Security Event ID 4769 for each SPN with TicketEncryptionType=0x17. Sysmon Event ID 1: Rubeus.exe process creation with 'kerberoast' argument. Sysmon Event ID 3: TCP connection to DC on port 88. Sysmon Event ID 11: file creation for rubeus_hashes.txt. Windows Defender may independently generate alerts for Rubeus.exe based on signature detection.
- Test 3Impacket GetUserSPNs — Linux-Based Kerberoasting
Expected signal: Domain Controller Security Event ID 4769 for each SPN with TicketEncryptionType=0x17, IpAddress field contains the Linux host IP. Event ID 4768 (TGT request) from Linux host IP preceding the 4769 events. No Sysmon telemetry (Linux source). DC Security logs capture the full activity. The source IP not matching any domain-joined Windows workstation is a high-fidelity anomaly indicator.
- Test 4Targeted Single-SPN Request via .NET KerberosRequestorSecurityToken
Expected signal: Domain Controller Security Event ID 4769: ServiceName=MSSQLSvc/sql01.corp.local:1433, TicketEncryptionType=0x17 (if target service account supports RC4). Sysmon Event ID 1: powershell.exe with 'KerberosRequestorSecurityToken' in CommandLine. PowerShell ScriptBlock Event ID 4104 with full .NET reflection code. Note: If the target account enforces AES-only encryption, EncryptionType will be 0x12 and detection will not fire on the RC4 rule — the account is not kerberoastable.
References (10)
- https://attack.mitre.org/techniques/T1558/003/
- https://blogs.technet.microsoft.com/motiba/2018/02/23/detecting-kerberoasting-activity-using-azure-security-center/
- https://adsecurity.org/?p=2293
- https://blog.harmj0y.net/powershell/kerberoasting-without-mimikatz/
- https://github.com/GhostPack/Rubeus
- https://github.com/fortra/impacket/blob/master/examples/GetUserSPNs.py
- https://learn.microsoft.com/en-us/windows/security/threat-protection/auditing/event-4769
- https://redsiege.com/kerberoast-slides
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1558.003/T1558.003.md
- https://www.crowdstrike.com/blog/meet-carbon-spider/
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