name: hunting-for-ntlm-relay-attacks description: Detect NTLM relay attacks by analyzing Windows Event 4624 logon type 3 with NTLMSSP authentication, identifying IP-to-hostname mismatches, Responder traffic signatures, SMB signing status, and suspicious authentication patterns across the domain. domain: cybersecurity subdomain: threat-hunting tags:

• NTLM-relay
• Windows-events
• Event-4624
• NTLMSSP
• Responder
• SMB-signing
• credential-access
• T1557.001
• Active-Directory version: '1.0' author: mahipal license: Apache-2.0 d3fend_techniques:
• Application Protocol Command Analysis
• Network Isolation
• Network Traffic Analysis
• Client-server Payload Profiling
• Network Traffic Community Deviation nist_csf:
• DE.CM-01
• DE.AE-02
• DE.AE-07
• ID.RA-05

Hunting for NTLM Relay Attacks

Overview

NTLM relay attacks intercept and forward NTLM authentication messages to gain unauthorized access to network resources. Attackers use tools like Responder for LLMNR/NBT-NS poisoning and ntlmrelayx for credential relay. This skill detects relay activity by querying Windows Security Event 4624 (successful logon) for type 3 network logons with NTLMSSP authentication, identifying mismatches between WorkstationName and source IpAddress, detecting rapid multi-host authentication from single accounts, and auditing SMB signing configuration across domain hosts.

When to Use

• When investigating security incidents that require hunting for ntlm relay attacks
• When building detection rules or threat hunting queries for this domain
• When SOC analysts need structured procedures for this analysis type
• When validating security monitoring coverage for related attack techniques

Prerequisites

• Python 3.9+ with Windows Event Log access or exported logs
• Windows Security audit logging enabled (Event ID 4624, 4625, 5145)
• Network access for SMB signing status checks

Key Detection Areas

1. IP-hostname mismatch — WorkstationName in Event 4624 does not resolve to the source IpAddress
2. NTLMSSP authentication — logon events using NTLM instead of Kerberos from domain-joined hosts
3. Machine account relay — computer accounts (ending in $) authenticating from unexpected IPs
4. Rapid authentication — single account authenticating to multiple hosts within seconds
5. Named pipe access — Event 5145 showing access to Spoolss, lsarpc, netlogon, samr pipes
6. SMB signing disabled — hosts not enforcing SMB signing, enabling relay attacks

Output

JSON report with suspected relay events, IP-hostname correlation anomalies, SMB signing audit results, and MITRE ATT&CK mapping to T1557.001.