Detect AS-REP Roasting in CrowdStrike LogScale
Adversaries may reveal credentials of accounts that have disabled Kerberos preauthentication by password cracking Kerberos AS-REP messages. When preauthentication is disabled on an account (userAccountControl flag DONT_REQ_PREAUTH), an attacker can send an AS-REQ message without an encrypted timestamp and receive an AS-REP response containing a TGT encrypted with the target account's password hash. This encrypted blob can be taken offline and cracked with tools like Hashcat or John the Ripper. The attack is commonly executed with Rubeus (asreproast module) or Impacket's GetNPUsers.py. Unlike Kerberoasting, AS-REP Roasting does not require a valid domain account to initiate — an unauthenticated attacker can send AS-REQ messages directly to the KDC. Successfully cracked credentials enable persistence, privilege escalation, and lateral movement via valid account access.
MITRE ATT&CK
- Tactic
- Credential Access
- Technique
- T1558 Steal or Forge Kerberos Tickets
- Sub-technique
- T1558.004 AS-REP Roasting
- Canonical reference
- https://attack.mitre.org/techniques/T1558/004/
LogScale Detection Query
// Detection 1: AS-REP Roasting via Windows Security Event 4768
// Requires CrowdStrike Falcon EventForwarder or Windows Security Event Log collection enabled on DCs
EventCode = "4768"
| PreAuthType = /^(0|0x0)$/
| !match(TargetUserName, regex=".*\\$$")
| EncryptionLabel := case {
TicketEncryptionType = "0x17" | "RC4-HMAC (crackable)";
TicketEncryptionType = "23" | "RC4-HMAC (crackable)";
TicketEncryptionType = "0x18" | "RC4-HMAC-EXP (crackable)";
TicketEncryptionType = "24" | "RC4-HMAC-EXP (crackable)";
TicketEncryptionType = "0x12" | "AES256-CTS (crackable offline)";
TicketEncryptionType = "18" | "AES256-CTS (crackable offline)";
TicketEncryptionType = "0x11" | "AES128-CTS";
TicketEncryptionType = "17" | "AES128-CTS";
* | "Unknown"
}
| WeakEncryption := if(
TicketEncryptionType = "0x17" or TicketEncryptionType = "23" or
TicketEncryptionType = "0x18" or TicketEncryptionType = "24",
true(), false()
)
| table(
[_time, ComputerName, TargetUserName, TargetDomainName, IpAddress, IpPort,
PreAuthType, EncryptionLabel, WeakEncryption, Status, TicketOptions],
sortby=_time, order=desc
)
// Detection 2: Bulk AS-REP Roasting — 3+ Unique Accounts from Same Source in 10-Minute Window
// EventCode = "4768"
// | PreAuthType = /^(0|0x0)$/
// | !match(TargetUserName, regex=".*\\$$")
// | bucket(field=_time, span=10min)
// | groupBy(
// [_time, IpAddress],
// function=[
// count(TargetUserName, as=TotalRequests),
// count(TargetUserName, distinct=true, as=UniqueAccounts),
// collect(TargetUserName, as=AccountsList)
// ]
// )
// | UniqueAccounts >= 3
// | sort(UniqueAccounts, order=desc)CrowdStrike LogScale (Humio) CQL queries detecting AS-REP Roasting via Windows Security Event 4768 collected through CrowdStrike Falcon Event Forwarding or Windows Event Log collection on domain controllers. Detection 1 identifies individual AS-REP requests with no preauthentication and labels encryption type to surface RC4-based (crackable) hashes. Detection 2 uses bucket/groupBy aggregation to detect bulk enumeration from a single source IP within a 10-minute window. Requires Windows Security Event forwarding to be enabled for domain controller assets in Falcon.
Data Sources
Required Tables
False Positives & Tuning
- Service accounts with DONT_REQ_PREAUTH enabled for cross-platform Kerberos compatibility (Linux/macOS AD-joined hosts, MIT Kerberos clients) generating routine single-account events from known static IPs that should be baselined and excluded
- Enterprise application servers (SAP, Oracle middleware) that authenticate multiple service accounts with preauthentication disabled from the same server IP during startup or scheduled tasks, potentially triggering the bulk enumeration threshold
- Authorised red team or internal penetration testing exercises targeting AD accounts with DONT_REQ_PREAUTH set — confirm with security team before escalating based on known testing windows
Other platforms for T1558.004
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 1AS-REP Roasting with Rubeus
Expected signal: Domain Controller Security Event ID 4768 for each roasted account with PreAuthType=0x0 and TicketEncryptionType=0x17 (RC4). Source IpAddress will be the attacking machine's IP. Sysmon Event ID 1 on attacking host: Process Create for Rubeus.exe with CommandLine containing 'asreproast'. Sysmon Event ID 3: network connections from Rubeus.exe to DC port 88 (Kerberos).
- Test 2AS-REP Roasting with Impacket GetNPUsers.py
Expected signal: Domain Controller Security Event ID 4768 for the target account with PreAuthType=0x0 and TicketEncryptionType=0x17. Source IpAddress will be the Linux/external attacking host's IP. No process creation event on the DC itself. If the attack originates from outside the domain, IpAddress will be a non-domain IP, which is a high-confidence indicator.
- Test 3PowerShell LDAP Enumeration of DONT_REQ_PREAUTH Accounts
Expected signal: Sysmon Event ID 1: PowerShell process creation with CommandLine containing 'DoesNotRequirePreAuth' or '4194304'. Domain Controller Event ID 4662 with ObjectType containing 'user' and AccessMask 0x10 (read property) — may generate many events. PowerShell ScriptBlock Log Event ID 4104 with the LDAP filter content.
- Test 4Manual AS-REQ without Preauthentication via PowerShell
Expected signal: Domain Controller Security Event ID 4768 for 'df00tech-asrep-test' with PreAuthType=0x0 and TicketEncryptionType=0x17. Security Event ID 4738 when preauthentication is disabled/re-enabled on the account. Rubeus.exe process creation (Sysmon Event ID 1) and network connection to DC port 88 (Sysmon Event ID 3).
References (10)
- https://attack.mitre.org/techniques/T1558/004/
- https://blog.harmj0y.net/activedirectory/roasting-as-reps/
- https://blog.stealthbits.com/cracking-active-directory-passwords-with-as-rep-roasting/
- https://docs.microsoft.com/en-us/windows/security/threat-protection/auditing/event-4768
- https://social.technet.microsoft.com/wiki/contents/articles/23559.kerberos-pre-authentication-why-it-should-not-be-disabled.aspx
- https://blogs.technet.microsoft.com/motiba/2018/02/23/detecting-kerberoasting-activity-using-azure-security-center/
- https://github.com/GhostPack/Rubeus
- https://github.com/fortra/impacket/blob/master/examples/GetNPUsers.py
- https://adsecurity.org/?p=2293
- https://redsiege.com/kerberoast-slides
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