Hunting For Ntlm Relay Attacks

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

Trigger phrases:

• "hunting for ntlm relay attacks"

• "Detect NTLM relay attacks by analyzing Windows Event 4624 logon type 3 with NTLM"

• 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

When NOT to Use

• When you lack proper authorization for testing
• For production systems without change management
• When the task requires legal or compliance expertise beyond technical scope

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

Red Flags

• Performing actions without explicit written authorization from the asset owner
• Testing against production systems without a defined scope and rules of engagement
• Exceeding the authorized scope of the engagement
• Leaving persistent access mechanisms without explicit approval
• Causing denial-of-service on production systems during testing

Verification

• All steps executed successfully against a test environment before production use
• Output documented with screenshots or logs demonstrating expected behavior
• All exploited vulnerabilities documented with reproduction steps
• Scope boundaries confirmed — only authorized targets were tested
• Remediation recommendations included for every finding

Output

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

Process

# Example: IOC detection
import re

IOC_PATTERNS = {
    "ip": r"\b(?:\d{1,3}\.){3}\d{1,3}\b",
    "domain": r"\b[a-z0-9-]+\.[a-z]{2,}\b",
    "hash_md5": r"\b[a-f0-9]{32}\b",
    "hash_sha256": r"\b[a-f0-9]{64}\b",
}

def extract_iocs(text: str) -> dict:
    return {k: re.findall(v, text) for k, v in IOC_PATTERNS.items()}

1. Analyze the task requirements
2. Apply domain expertise
3. Verify output quality

Anti-Rationalization Table