Detecting NTLM Relay with Event Correlation

Authorized Testing Disclaimer: The offensive techniques and attack simulations described in this skill are intended exclusively for authorized penetration testing, red team engagements, purple team exercises, and security research conducted with explicit written permission from the system owner. Unauthorized use of these techniques against systems you do not own or have permission to test is illegal and unethical. Always operate within the scope of your engagement and comply with applicable laws and regulations.

Overview

NTLM relay attacks intercept NTLM authentication messages and forward them to a target service to gain unauthorized access. Attackers use tools like Responder for LLMNR/NBT-NS/mDNS poisoning, ntlmrelayx (Fox-IT/Impacket) for multi-protocol relay, and coercion techniques like PetitPotam (MS-EFSRPC) and DFSCoerce to force authentication from high-value targets like domain controllers. This skill provides a comprehensive event correlation framework using Windows Security Event 4624 LogonType 3 analysis, IP-to-hostname mismatch detection, Responder traffic identification, SMB/LDAP signing audit, and NTLM downgrade detection to identify relay attacks across Active Directory environments.

When to Use

• Hunting for credential relay activity in Active Directory environments where NTLM authentication is still in use
• Investigating alerts for authentication anomalies where the source IP does not match the expected workstation
• Auditing SMB signing and LDAP signing enforcement to assess exposure to relay attacks
• Detecting NTLM downgrade attacks where NTLMv2 is forced to NTLMv1 for easier offline cracking or relay
• Building SIEM correlation rules for MITRE ATT&CK T1557.001 (LLMNR/NBT-NS Poisoning and SMB Relay)
• Responding to PetitPotam, DFSCoerce, or PrinterBug coercion alerts that may precede relay attacks
• During purple team exercises validating NTLM relay detection and SMB signing enforcement

Do not use without centralized Windows Security Event Log collection, as a substitute for enforcing SMB signing and Extended Protection for Authentication (EPA) which prevent relay attacks at the protocol level, or without an IP-to-hostname inventory for correlation.