2025-02-09
What is Link-Local Multicast Name Resolution (LLMNR)?
Link-Local Multicast Name Resolution (LLMNR) is a protocol based on the Domain Name System (DNS) packet format. It allows both IPv4 and IPv6 hosts to perform name resolution for devices on the same local network without relying on a DNS server. This protocol is particularly useful when DNS servers are unavailable, enabling devices to resolve hostnames locally.
How Does LLMNR Work?
When a device needs to resolve a hostname on the local network, it sends an LLMNR query to a multicast group address. This query is broadcasted to all devices on the network, asking if any device knows the IP address associated with the requested hostname. If a device recognizes the hostname, it responds directly with the corresponding IP address. However, LLMNR transmits data in plain text, making it vulnerable to sniffing attacks. Attackers can exploit this weakness to intercept sensitive information, such as usernames and password hashes.
LLMNR Poisoning and Responder Tool
LLMNR poisoning is a common attack vector where an attacker listens for LLMNR queries and responds with malicious intent. One of the most popular tools for exploiting LLMNR is Responder. This tool listens for LLMNR, NetBIOS Name Service (NBT-NS), and DNS traffic, allowing attackers to capture credentials and hashes. Once the attacker obtains a hash, they can use tools like Hashcat to crack it and gain unauthorized access to systems.
Practical Example: Using Responder
To demonstrate how LLMNR poisoning works, here’s a basic example of using Responder on a Linux system:
1. Install Responder:
sudo apt-get update sudo apt-get install responder
2. Run Responder:
sudo responder -I eth0
Replace `eth0` with your network interface. Responder will now listen for LLMNR, NBT-NS, and DNS queries.
3. Capture Hashes:
When a victim device sends an LLMNR query, Responder will capture the username and NTLMv2 hash. These hashes can be saved to a file for offline cracking.
4. Crack the Hash with Hashcat:
Use Hashcat to crack the captured hash:
hashcat -m 5600 hash.txt wordlist.txt
Replace `hash.txt` with the file containing the captured hash and `wordlist.txt` with your preferred wordlist.
Mitigation Strategies
To protect against LLMNR poisoning, consider the following measures:
– Disable LLMNR and NBT-NS on all devices in your network.
– Use DNS securely and ensure DNS servers are always available.
– Implement network segmentation to limit the spread of attacks.
– Monitor network traffic for unusual LLMNR or NBT-NS activity.
What Undercode Say
LLMNR poisoning is a significant threat to network security, especially in environments where DNS servers are unreliable or unavailable. By understanding how LLMNR works and how attackers exploit it, you can take proactive steps to secure your network. Disabling LLMNR and NBT-NS is a critical first step, but it’s also essential to monitor network traffic and implement strong authentication mechanisms. Tools like Responder and Hashcat highlight the importance of securing credentials and using robust password policies. Additionally, consider using encrypted protocols like DNS over HTTPS (DoH) or DNS over TLS (DoT) to further enhance security. Regularly updating your systems and educating users about phishing and social engineering attacks can also reduce the risk of credential theft. For more information on securing your network, visit OWASP’s guide to LLMNR/NBT-NS poisoning.
By following these best practices and leveraging Linux commands like `systemctl disable llmnr` and systemctl disable netbios, you can significantly reduce the risk of LLMNR poisoning and protect your network from unauthorized access.
References:
Hackers Feeds, Undercode AI
