Detect LLMNR/NBT-NS Poisoning and SMB Relay in CrowdStrike LogScale
Adversaries may spoof an authoritative source for name resolution to force communication with an adversary-controlled system, collecting or relaying authentication materials. By responding to LLMNR (UDP 5355) and NBT-NS (UDP 137) queries, attackers poison name resolution so that victims authenticate to the adversary system, capturing NTLMv1/v2 hashes for offline cracking or relay attacks. Captured hashes may be relayed directly to SMB, LDAP, MSSQL, or HTTP services to authenticate as the victim without ever cracking the hash. Tools such as Responder, Inveigh, Impacket ntlmrelayx, and NBNSpoof are commonly used. Threat actors including Lazarus Group and Wizard Spider have used this technique for credential collection and lateral movement.
MITRE ATT&CK
- Tactic
- Credential Access Collection
- Technique
- T1557 Adversary-in-the-Middle
- Sub-technique
- T1557.001 LLMNR/NBT-NS Poisoning and SMB Relay
- Canonical reference
- https://attack.mitre.org/techniques/T1557/001/
LogScale Detection Query
#event_simpleName = ProcessRollup2
| ImageFileName = /(?i)(responder\.exe|inveigh\.exe|ntlmrelayx\.exe|smbrelayx\.exe|multirelay\.exe|nbnspoof\.exe|conveigh\.exe)/
OR CommandLine = /(?i)(Responder|Inveigh|Invoke-Inveigh|ntlmrelayx|smbrelayx|MultiRelay|NBNSpoof|llmnr_response|-rPv|Inveigh-Unprivileged)/
OR (ImageFileName = /(?i)python[23]?\.exe/ AND CommandLine = /(?i)(responder|inveigh|ntlmrelayx|smbrelayx|multirelay|nbnspoof|llmnr_response)/)
| case {
ImageFileName = /(?i)(responder\.exe|inveigh\.exe|ntlmrelayx\.exe|smbrelayx\.exe|multirelay\.exe|nbnspoof\.exe|conveigh\.exe)/ | IsKnownTool := "true";
* | IsKnownTool := "false"
}
| case {
ImageFileName = /(?i)python[23]?\.exe/ AND CommandLine = /(?i)(responder|inveigh|ntlmrelayx|smbrelayx|multirelay|nbnspoof|llmnr_response)/ | IsPythonPoisoner := "true";
* | IsPythonPoisoner := "false"
}
| case {
CommandLine = /(?i)(invoke-inveigh|inveigh-unprivileged|inveigh)/ | HasInveigh := "true";
* | HasInveigh := "false"
}
| case {
CommandLine = /(?i)(ntlmrelayx|smbrelayx|multirelay|-rpv)/ | HasRelay := "true";
* | HasRelay := "false"
}
| table([ComputerName, UserName, ImageFileName, CommandLine, ParentBaseFileName, IsKnownTool, IsPythonPoisoner, HasInveigh, HasRelay])
| sort(@timestamp, order=desc, limit=200)Detects LLMNR/NBT-NS poisoning and SMB relay tool execution in CrowdStrike Falcon via LogScale CQL querying ProcessRollup2 events. Filters on known poisoning binary names via case-insensitive regex, Python interpreter instances with poisoning command-line arguments, and broad keyword patterns covering Responder, Inveigh, ntlmrelayx, and related tools. Per-event enrichment flags (IsKnownTool, IsPythonPoisoner, HasInveigh, HasRelay) enable analyst triage prioritization. Requires Falcon Insight XDR or equivalent process telemetry license.
Data Sources
Required Tables
False Positives & Tuning
- Authorized red team operators using Responder or ntlmrelayx from pre-approved endpoints or under documented service accounts — add ComputerName or UserName exclusions for known red team assets.
- Python-based DevOps tooling, REST API clients, or internal automation scripts whose command-line arguments include strings overlapping with poisoning tool names (e.g., 'auto-responder.py', 'relay-agent', 'invoke-workflow').
- Security tooling vendors or SIEM management scripts that spawn Python subprocesses with script names containing 'inveigh', 'relay', or 'responder' as functional labels for unrelated network communication tasks.
Other platforms for T1557.001
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 1Invoke-Inveigh LLMNR and NBT-NS Poisoning via PowerShell
Expected signal: Sysmon Event ID 1: powershell.exe with CommandLine containing 'Invoke-Inveigh', 'Net.WebClient', and 'DownloadString'. Sysmon Event ID 3: PowerShell process binding/connecting on UDP 5355 and UDP 137. PowerShell ScriptBlock Log Event ID 4104 capturing the full Inveigh module code and runtime output. Sysmon Event ID 22 (DNS Query) for the GitHub download request.
- Test 2Responder Python Execution in Analyze Mode
Expected signal: Sysmon Event ID 1: python3.exe with CommandLine containing 'Responder.py' and '-I'. Sysmon Event ID 3: python3.exe binding on UDP 5355 (LLMNR) and UDP 137 (NBT-NS). DeviceNetworkEvents: InitiatingProcessFileName=python3.exe with LocalPort=5355 or 137. DeviceProcessEvents: FileName=python3.exe, ProcessCommandLine contains 'Responder'.
- Test 3Impacket ntlmrelayx Relay Tool Execution Against Loopback Target
Expected signal: Sysmon Event ID 1: python3.exe with CommandLine containing 'ntlmrelayx.py', '-t', and 'smb://'. Sysmon Event ID 3: python3.exe attempting TCP connection to 127.0.0.1:445. DeviceProcessEvents: FileName=python3.exe, ProcessCommandLine contains 'ntlmrelayx'. Connection will fail (no SMB listener on loopback) but all process creation telemetry fires.
- Test 4Disable LLMNR and NBT-NS via Registry — Defensive Control Validation
Expected signal: Sysmon Event ID 13 (Registry Value Set): HKLM\SOFTWARE\Policies\Microsoft\Windows NT\DNSClient\EnableMulticast set to DWORD 0. Sysmon Event ID 1: powershell.exe with CommandLine containing 'Win32_NetworkAdapterConfiguration' and 'SetTcpipNetbios'. Security Event ID 4657 (if Object Access auditing enabled): registry key modification logged.
References (12)
- https://attack.mitre.org/techniques/T1557/001/
- https://github.com/SpiderLabs/Responder
- https://github.com/Kevin-Robertson/Inveigh
- https://byt3bl33d3r.github.io/practical-guide-to-ntlm-relaying-in-2017-aka-getting-a-foothold-in-under-5-minutes.html
- https://blog.secureideas.com/2018/04/ever-run-a-relay-why-smb-relays-should-be-on-your-mind.html
- https://github.com/SecureAuthCorp/impacket
- https://www.sternsecurity.com/blog/local-network-attacks-llmnr-and-nbt-ns-poisoning
- https://github.com/nomex/nbnspoof
- https://www.rapid7.com/db/modules/auxiliary/spoof/llmnr/llmnr_response
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1557.001/T1557.001.md
- https://learn.microsoft.com/en-us/defender-endpoint/advanced-hunting-devicenetworkevents-table
- https://learn.microsoft.com/en-us/windows-server/networking/technologies/netbios/netbios
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