Identify and Eliminate Insecure Hostname Queries

Hostname queries are an essential part of network communication, but not all methods for hostname resolution are secure. This chapter covers what insecure hostname queries are, how adversaries can exploit them, and steps for blocking these vulnerabilities to safeguard your network.

What Is an Insecure Hostname Query?

Definition: Insecure hostname queries are resolution methods that can be exploited by attackers due to their broadcast nature or lack of strong security measures. Two common types of insecure hostname queries are Link-Local Multicast Name Resolution (LLMNR) and Multicast DNS (mDNS):

• LLMNR: A protocol used to resolve hostnames when DNS is not available. It operates on a local network by broadcasting hostname requests.
• mDNS: Similar to LLMNR but primarily used in home or small office networks. It resolves hostnames by multicasting queries to other devices on the same local network.

Why These Protocols Are Considered Insecure:

• Lack of Authentication: LLMNR and mDNS do not have strong built-in authentication, allowing attackers to respond to hostname queries with malicious IP addresses.
• Broadcast Communication: They broadcast requests to all devices on the local network, which can easily be intercepted or spoofed.
• Man-in-the-Middle Potential: Attackers can impersonate legitimate devices and redirect traffic to malicious endpoints, leading to data interception or unauthorized access.

How Adversaries Use Insecure Hostname Queries

Attackers leverage insecure hostname queries in various ways to compromise networks:

• Responder Attacks: In this common method, attackers use tools like Responder to poison LLMNR or mDNS queries. When a device broadcasts a request for a hostname, the tool tricks the device into believing that the attacker's system is the requested resource. This enables attackers to capture credentials or reroute traffic.
• Credential Theft: By spoofing legitimate responses, attackers can trick users into sending their login details, which are then harvested for later use in more advanced attacks.
• Network Mapping and Reconnaissance: Adversaries can use the responses from LLMNR and mDNS to gather information about the devices and services available on the network, building a blueprint of the network structure to identify potential targets.
• Downgrade Attacks: Attackers may force a client to use an insecure hostname resolution method by disrupting standard DNS services, creating an opportunity to intercept communications.

How to Block Insecure Hostname Queries

Blocking or mitigating insecure hostname queries helps strengthen network security. Here’s how to do it:

A. On Windows Systems

1. Disable LLMNR:
   • Use Group Policy to disable LLMNR across the domain:
     • Open Group Policy Management and create or edit an existing GPO.
     • Navigate to Computer Configuration > Administrative Templates > Network > DNS Client.
     • Set Turn off multicast name resolution to Enabled.
2. Disable mDNS:
   • There is no direct Group Policy for mDNS, but you can use PowerShell or registry tweaks to disable specific services that utilize mDNS.

B. On Linux Systems

1. Disable LLMNR:

   • For systems using systemd-resolved, add or edit the configuration in /etc/systemd/resolved.conf:

     [Resolve]
     LLMNR=no
     MulticastDNS=no
     

   • Restart the service with sudo systemctl restart systemd-resolved.

2. Disable mDNS:

   • If avahi-daemon is installed (commonly used for mDNS services), stop and disable it:

     sudo systemctl stop avahi-daemon
     sudo systemctl disable avahi-daemon
     

C. Network-Level Mitigation

• Network Segmentation: Use VLANs or network segmentation to isolate groups of devices that do not need to communicate via LLMNR or mDNS.
• Firewall Rules: Block multicast traffic related to LLMNR and mDNS at the network perimeter. Specifically:
  • Block UDP traffic on port 5353 (mDNS) and port 5355 (LLMNR).

D. Leverage Ridgeback for Detection and Prevention

• Monitor Network Traffic: Ridgeback analyzes network metadata to identify patterns that indicate LLMNR or mDNS queries. This helps network administrators spot unusual or potentially malicious activity.
• Alerting and Reporting: Ridgeback can be configured to alert administrators when insecure hostname queries are detected, allowing for swift action.
• Policy Enforcement: Use Ridgeback's insights to enforce stricter network policies and reduce reliance on insecure protocols, enhancing your overall security posture.

Conclusion

Identifying and eliminating insecure hostname queries is a crucial step in protecting your network from credential theft, unauthorized access, and other malicious activities. By disabling LLMNR and mDNS, employing network-level controls, and using tools like Ridgeback to monitor traffic, you can significantly reduce the attack surface and improve the resilience of your network infrastructure.