Anthropic-Cybersecurity-Skills/skills/hunting-for-ntlm-relay-attacks/references/api-reference.md

NTLM Relay Attack Detection Reference

Windows Event IDs

Event ID	Log	Description
4624	Security	Successful logon — primary relay detection event
4625	Security	Failed logon — may indicate relay attempts
5145	Security	Network share object access — named pipe monitoring
4776	Security	NTLM credential validation

Event 4624 Fields for Relay Detection

Field	Suspicious Value	Significance
LogonType	3 (Network)	Relay always produces network logon
AuthenticationPackageName	NTLMSSP	NTLM used instead of Kerberos
LmPackageName	NTLM V1	Downgraded to NTLMv1 (very suspicious)
WorkstationName	Mismatch with IpAddress	Key relay indicator
TargetUserSid	S-1-0-0 (NULL SID)	Unauthenticated relay attempt
LogonGuid	{00000000-...}	Empty GUID indicates relay
ImpersonationLevel	Impersonation	Relay uses impersonation

Suspicious Named Pipes (Event 5145)

Pipe Name	Service	Relay Target
spoolss	Print Spooler	PrinterBug/SpoolSample
lsarpc	LSA	PetitPotam, DFSCoerce
netlogon	Netlogon	ZeroLogon relay
samr	SAM	User enumeration
efsrpc	EFS	PetitPotam
netdfs	DFS	DFSCoerce
srvsvc	Server Service	General relay

Splunk Detection Query

index=wineventlog EventCode=4624 Logon_Type=3 Authentication_Package=NTLM
| eval hostname_ip_match=if(Workstation_Name==src_ip OR isnull(Workstation_Name), "match", "mismatch")
| where hostname_ip_match="mismatch"
| stats count values(src_ip) as source_ips values(Workstation_Name) as workstations by Account_Name, Computer
| where count > 3

Elastic EQL Detection (NTLM Relay Against Computer Account)

sequence by winlog.computer_name with maxspan=5s
  [any where event.code == "5145" and
    winlog.event_data.RelativeTargetName in ("spoolss","netdfs","lsarpc","samr","efsrpc","netlogon") and
    winlog.event_data.SubjectUserName != winlog.computer_name]
  [authentication where event.code in ("4624","4625") and
    winlog.event_data.AuthenticationPackageName == "NTLM" and
    winlog.event_data.LogonType == "3" and
    winlog.event_data.TargetUserName : "*$"]

PowerShell Detection

# Query NTLM type 3 logons
Get-WinEvent -FilterHashtable @{LogName='Security'; Id=4624} |
  Where-Object {
    $_.Properties[8].Value -eq 3 -and
    $_.Properties[14].Value -match 'NTLM'
  } | Select-Object TimeCreated,
    @{N='User';E={$_.Properties[5].Value}},
    @{N='Workstation';E={$_.Properties[11].Value}},
    @{N='SourceIP';E={$_.Properties[18].Value}},
    @{N='AuthPkg';E={$_.Properties[14].Value}}

# Check SMB signing
Get-SmbServerConfiguration | Select-Object RequireSecuritySignature, EnableSecuritySignature

SMB Signing Enforcement

# Enable SMB signing (require on server)
Set-SmbServerConfiguration -RequireSecuritySignature $true -Force

# Group Policy path
# Computer Configuration > Policies > Windows Settings > Security Settings >
# Local Policies > Security Options >
# Microsoft network server: Digitally sign communications (always): Enabled

Common Relay Tools (Detection Signatures)

Tool	Network Signature
Responder	LLMNR/NBT-NS responses from non-authoritative source
ntlmrelayx	Rapid sequential NTLM auth from single source IP
PetitPotam	EFS RPC calls to \attacker\share via lsarpc pipe
PrinterBug	RPC call to spoolss pipe targeting attacker listener
mitm6	DHCPv6 responses with rogue DNS server

MITRE ATT&CK Mapping

• T1557.001 — Adversary-in-the-Middle: LLMNR/NBT-NS Poisoning and SMB Relay
• T1187 — Forced Authentication
• T1003.001 — OS Credential Dumping: LSASS Memory
• TA0006 — Credential Access (Tactic)

Response Checklist

1. Enable SMB signing on all domain hosts via GPO
2. Disable LLMNR: Set-DnsClientGlobalSetting -SuffixSearchList @("")
3. Disable NBT-NS in network adapter advanced settings
4. Enable Extended Protection for Authentication (EPA)
5. Enforce NTLMv2 and deny NTLMv1: LmCompatibilityLevel = 5
6. Deploy SMB signing GPO: RequireSecuritySignature = 1