CyberStack

MITRE ATT&CK / Techniques / T1557.001

Adversary-in-the-Middle: Name Resolution Poisoning and SMB Relay

ID
T1557.001
Tactics
TA0006 Credential Access, TA0009 Collection
Sub-technique of
T1557 Adversary-in-the-Middle
Platforms
Windows
Data sources
Service Creation, Windows Registry Key Modification, Network Traffic Content, Network Traffic Flow
Source
attack.mitre.org
MITRE last modified
12 May 2026

By responding to LLMNR/NBT-NS/mDNS network traffic, adversaries may spoof an authoritative source for name resolution to force communication with an adversary controlled system.[5] This activity may be used to collect or relay authentication materials.

Link-Local Multicast Name Resolution (LLMNR) and NetBIOS Name Service (NBT-NS) are Microsoft Windows components that serve as alternate methods of host identification. LLMNR is based upon the Domain Name System (DNS) format and allows hosts on the same local link to perform name resolution for other hosts. NBT-NS identifies systems on a local network by their NetBIOS name.[6][7]

Multicast Domain Name System(mDNS) is a zero-configuration service used to resolve hostnames to IP addresses with “.local” as a top-level domain. MDNS is based upon Domain Name System (DNS) format and allows hosts on the same network segment to perform name resolution for other hosts, using multicast.[8]

Adversaries can spoof an authoritative source for name resolution on a victim network by responding to LLMNR (UDP 5355)/NBT-NS (UDP 137)/mDNS (UDP 5353) traffic as if they know the identity of the requested host, effectively poisoning the service so that the victims will communicate with the adversary controlled system. If the requested host belongs to a resource that requires identification/authentication, the username and NTLMv2 hash will then be sent to the adversary controlled system. The adversary can then collect the hash information sent over the wire through tools that monitor the ports for traffic or through Network Sniffing and crack the hashes offline through Brute Force to obtain the plaintext passwords.

In some cases where an adversary has access to a system that is in the authentication path between systems or when automated scans that use credentials attempt to authenticate to an adversary controlled system, the NTLMv1/v2 hashes can be intercepted and relayed to access and execute code against a target system. The relay step can happen in conjunction with poisoning but may also be independent of it.[1][2] Additionally, adversaries may encapsulate the NTLMv1/v2 hashes into various other protocols, such as LDAP, MSSQL and HTTP, to expand and use multiple services with the valid NTLM response. 

Several tools may be used to poison name services within local networks such as NBNSpoof, Metasploit, and Responder.[9][10][11]

Detection

Mitigations (4)

M1030 Network Segmentation

Network segmentation can be used to isolate infrastructure components that do not require broad network access. This may mitigate, or at least alleviate, the scope of AiTM activity.

M1031 Network Intrusion Prevention

Network intrusion detection and prevention systems that can identify traffic patterns indicative of AiTM activity can be used to mitigate activity at the network level.

M1037 Filter Network Traffic

Use host-based security software to block LLMNR/NetBIOS/mDNS traffic. Enabling SMB Signing can stop NTLMv2 relay attacks.[1][2][3]

M1042 Disable or Remove Feature or Program

Disable LLMNR, mDNS, and NetBIOS in local computer security settings or by group policy if they are not needed within an environment. [4]

Groups (2)

Software (5)

References

  1. byt3bl33d3r NTLM Relaying
  2. Secure Ideas SMB Relay
  3. Microsoft SMB Packet Signing
  4. ADSecurity Windows Secure Baseline
  5. BlackCat ransomware
  6. Wikipedia LLMNR
  7. TechNet NetBIOS
  8. mDNS RFC
  9. GitHub NBNSpoof
  10. Rapid7 LLMNR Spoofer
  11. GitHub Responder