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TB Noxious

by C. Casquatch

LLMNR Poisoning Walkthrough

Scenario Overview

The IDS device alerted us to a possible rogue device on the internal Active Directory network. It also flagged unusual LLMNR traffic directed towards Forela-WKstn002 (IP: 172.17.79.136). As a Network Forensics expert, you are asked to investigate potential LLMNR poisoning on the Active Directory VLAN.

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What is LLMNR Poisoning?

TCM Security’s article provides an excellent explanation:

• LLMNR (Link-Local Multicast Name Resolution) is used when DNS fails to resolve hostnames on a local network.
• It lacks authentication, which allows attackers to spoof replies and intercept sensitive data (like usernames and password hashes).
• Tools like Responder automate these attacks, capturing hashes that can be cracked offline with tools like Hashcat.
• Mitigation includes disabling LLMNR/NBT-NS, enforcing strong password policies, and patching systems regularly.

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Step-by-Step Analysis

Step 1: Identify Most Active IPs

Open Statistics -> Endpoints in Wireshark to view the top talkers. Look for IPs close to 172.17.79.136 to understand the internal IP layout.

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Step 2: Find the Malicious IP Address

• Filter LLMNR traffic using: udp.port == 5355
• Look for responses to queries from 172.17.79.136. Only one IP responds – this is our suspected rogue machine.
• This IP is not the domain controller.

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Step 3: Identify Hostname of the Rogue Device

• Use filter: ip.addr == 172.17.79.135 && dhcp
• Check DHCP packets for the hostname value.

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Step 4: Confirm Hash Capture & Find the Username

• Use smb2 to locate SMB traffic.
• Then filter further with ntlmssp.
• Look for NTLMSSP_AUTH packets – you’ll find the username here.

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Step 5: Find the First Time the Hash Was Captured

• Make sure your time format is set to UTC.
• Check the timestamp on the first NTLMSSP_AUTH packet.

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Step 6: Identify the Victim’s Typo

• Look for the hostname the victim tried to access.
• They mistyped DC01 as DCC01.

Hint: Domain Controller Controller? Oops.

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Step 7: Extract NTLM Server Challenge Value

• Add ntlmssp filter again.
• Go to the NTLMSSP_CHALLENGE packet.
• Path: SMB2 -> Session Setup Response -> Security Blob -> NTLM Server Challenge

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Step 8: Find the NTProofStr Value

• Locate the NTLMSSP_AUTH packet just after the challenge.
• Navigate similarly through the protocol stack to find NTProofStr.

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Step 9: Crack the Captured Hash

• Construct your hash in the following format:

  Username::Domain:ServerChallenge:NTProofStr:NTLMv2Response (without first 16 bytes)
  

• Save to a file and use:

  hashcat -a 0 -m 5600 /path/to/file/hashfile.txt /path/to/file/rockyou.txt
  

Note: Don’t forget the colon after NTProofStr – it’ll save you 30 minutes of frustration.

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Step 10: Identify the Target File Share

• Use smb2 filter.
• Look for a non-default file share with a tree connect/disconnect.
• The name should suggest why the attacker was interested.

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tags: ntlm - LLMNR - htb - noxious - wireshark