Spoofing LLMNR, NBT-NS, mDNS/DNS and WPAD and Relay Attacks

Network protocols


Microsoft systems use Link-Local Multicast Name Resolution (LLMNR) and the NetBIOS Name Service (NBT-NS) for local host resolution when DNS lookups fail. Apple Bonjour and Linux zero-configuration implementations use Multicast DNS (mDNS) to discover systems within a network. These protocols are unauthenticated and broadcast messages over UDP; thus, attackers can exploit them to direct users to malicious services.

You can impersonate services that are searched by hosts using Responder to send fake responses. Read here more information about how to Impersonate services with Responder.


Many browsers use Web Proxy Auto-Discovery (WPAD) to load proxy settings from the network. A WPAD server provides client proxy settings via a particular URL (e.g., http://wpad.example.org/wpad.dat) upon being identified through any of the following:

  • DHCP, using a code 252 entry34

  • DNS, searching for the wpad hostname in the local domain

  • Microsoft LLMNR and NBT-NS (in the event of DNS lookup failure)

Responder automates the WPAD attack—running a proxy and directing clients to a malicious WPAD server via DHCP, DNS, LLMNR, and NBT-NS.


Responder an LLMNR, NBT-NS and MDNS poisoner. It will answer to specific NBT-NS (NetBIOS Name Service) queries based on their name suffix (see: http://support.microsoft.com/kb/163409). By default, the tool will only answer to File Server Service request, which is for SMB.

The concept behind this is to target our answers, and be stealthier on the network. This also helps to ensure that we don't break legitimate NBT-NS behavior. You can set the -r option via command line if you want to answer to the Workstation Service request name suffix.

Responder is installed in kali by default and the config file is located in /etc/responder/Responder.conf You can find here Responder for windows here: https://github.com/lgandx/Responder-Windows __To run default Responder behaviour you only have to execute:

responder -I <Iface>

An interesting technique is to use responder to downgrade the NTLM authentication when possible. This will allow to capture NTLMv1 challenges and responses instead of NTLMv2 that can be easily cracked following this guide.

#Remember that in order to crack NTLMv1 you need to set Responder challenge to "1122334455667788"
responder -I <Iface> --lm #Downgrade NTLM authntication if possible

By default, the WPAD impersonation won't be executed, but you can execute it doing:

responder -I <Iface> --wpad

Responder can also send fake DNS responses (so the IP of the attacker is resolved) and can inject PAC files so the victim will get the IP of the attacker as a proxy.

responder.py -I <interface> -w On #If the computer detects the LAN configuration automatically, this will impersonate it

You can also resolve NetBIOS requests with your IP. And create an authentication proxy:

responder.py -I <interface> -rPv

You won't be able to intercept NTLM hashes (normally), but you can easily grab some NTLM challenges and responses that you can crack using for example john option --format=netntlmv2.

The logs and the challenges of default Responder installation in kali can be found in /usr/share/responder/logs

Capturing credentials

Responder is going to impersonate all the service using the mentioned protocols. Once some user try to access a service being resolved using those protocols, he will try to authenticate against Responder and Responder will be able to capture the "credentials" (most probably a NTLMv2 Challenge/Response):


Inveigh is a PowerShell ADIDNS/LLMNR/NBNS/mDNS/DNS spoofer and man-in-the-middle tool designed to assist penetration testers/red teamers that find themselves limited to a Windows system.

Inveigh is a PowerShell script that has the same main features as Responder.

Relay Attack

Most of the information for this section was taken from https://intrinium.com/smb-relay-attack-tutorial/****

This attack uses the Responder toolkit to capture SMB authentication sessions on an internal network, and relays them to a target machine. If the authentication session is successful, it will automatically drop you into a system shell. Please, note that the relayed authentication must be from a user which has Local Admin access to the relayed host and SMB signing must be disabled.

The 3 main tools to perform this attack are: smb_relay (metasploit), MultyRelay (responder), and smbrealyx (impacket).

Independently of the tool, first, you need to turn Off SMB and HTTP servers in **_/usr/share/responder/Responder.conf_ and then execute responder on the desired interface**: responder -I eth0 -rv

You can perform this attack using metasploit module: exploit/windows/smb/smb_relay The option SRVHOST is used to point the server were you want to get access. Then, when any host try to authenticate against you, metasploit will try to authenticate against the other server.

You can't authenticate against the same host that is trying to authenticate against you (MS08-068). Metasploit will always send a "Denied" response to the client that is trying to connect to you.

If you want to use smbrelayx now you should run:

smbrelayx.py -h <IP target> -c "ipconfig"

If you want to use MultiRelay, go to /usr/share/responder/tools and execute MultiRelay (-t <IP target> -u <User>):

python MultiRelay.py -t <IP target> -u ALL #If "ALL" then all users are relayed

Post-Exploitation (MultiRelay)

At this point you can shut off Responder; we don’t need it anymore. With the shell access we have obtained, there are many actions that we can perform directly from here:

Mimikatz commands can also be performed directly from the shell. Unfortunately, the target used for this tutorial’s antivirus ate my mimikatz, but the following commands can be executed to run mimikatz, as well as the entire pallette of modules.: Mimi sekurlsa::logonpasswords


InveighZero is a C# LLMNR/NBNS/mDNS/DNS/DHCPv6 spoofer and man-in-the-middle tool designed to assist penetration testers/red teamers that find themselves limited to a Windows system. This version shares many features with the PowerShell version of Inveigh. More information in the github of the project.

Force Privileged Accounts to login via NTLM

In Windows you may be able to force some privileged accounts to authenticate to arbitrary machines. Read the following page to learn how:

Force NTLM Privileged Authentication


Disabling LLMNR

To disable LLMNR in your domain for DNS clients, open gpedit.msc. Navigate to Computer Configuration->Administrative Templates->Network->DNS client. Locate the option “Turn off multicast name resolution” and click “policy setting”:

Once the new window opens, enable this option, press Apply and click OK:

Disabling NBT-NS

One option for disabling NBT-NS is to use DHCP scope options.

If using Microsoft's DHCP server, select the scope that you want to disable NBT-NS for. Right click “Scope Options” and click “Configure Options”. In the example below, the DHCP scope in which I want to disable NBT-NS for is

In the Scope Options window, navigate to the advanced tab, change the drop down window to “Microsoft Windows 2000 Options”:

Select the option “001 Microsoft Disable Netbios Option” from the list and change its value to “0x2”, click Apply and then OK:


To mitigate against the WPAD attack, you can add an entry for "wpad" in your DNS zone. Note that the DNS entry does not need to point to a valid WPAD server. As long as the queries are resolved, the attack will be prevented.


  1. Forcing SMB Signing on all local windows machines. This setting will digitally sign each and every SMB session which forces both the client and server to verify the source of the packets before continuing. This setting is only enabled by default on Domain Controllers. The following articles from Microsoft detail these settings (which can be enabled through group policy), and how to implement them.



  1. Reviewing and ensuring that the users on the local network can only remotely login to machines in which it is necessary. For example: Sally can only log in to Sally’s workstation. If an attacker were to intercept Sally’s SMB Auth session, they could not relay the session to any workstations, rendering this method useless.

  2. Restrict NTLM Authentication on the local network as much as possible. This attack cannot take advantage of Kerberos authentication, so by limiting the amount of NTLM that’s occurring, this attack can be greatly hindered. There is information from Microsoft on making this happen, but be warned.. If Kerberos authentication fails for whatever reason, it generally falls back onto NTLM. If you disable it entirely, your network might grind to a halt.

  3. Prevent unauthorised users on your network. An insider threat will likely not be utilising an SMB Relay attack, as they already have network credentials. By beefing up your physical security policies, preventing rogue devices on the network with ACLs and MAC Filtering, and ensuring proper network segmentation, you can greatly limit the threat of this attack being performed.


Images from: https://www.4armed.com/blog/llmnr-nbtns-poisoning-using-responder/ https://www.notsosecure.com/pwning-with-responder-a-pentesters-guide/ https://intrinium.com/smb-relay-attack-tutorial/ https://byt3bl33d3r.github.io/practical-guide-to-ntlm-relaying-in-2017-aka-getting-a-foothold-in-under-5-minutes.html

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