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Responder is a tool that exploits vulnerabilities in network protocols like LLMNR, NBT-NS and MDNS to capture authentication credentials. It works by impersonating legitimate network services and tricking devices into sending sensitive information. Used in penetration testing, it’s also a worry in unauthorized network exploitation.
Responder listens for broadcasted network queries that try to resolve hostnames. When a device can’t resolve a hostname using standard methods, it falls back on protocols like LLMNR or NBT-NS and broadcasts a request to the local network. Responder responds to these requests with its own IP address, impersonating the destination.
Credential Capture Mechanism
Once a device connects, thinking Responder is the legitimate service, it often sends authentication credentials. These credentials can then be analyzed or cracked offline. This is particularly effective in networks where these old protocols are still enabled, as they don’t have robust verification mechanisms.
Ethical and Legal Implications
While Responder is a great tool to identify network weaknesses, it should only be used in authorized security assessments. Unauthorized deployment can be a big legal problem. Organizations should disable unnecessary name resolution protocols and enforce strong network defenses to prevent misuse.
Disable LLMNR and NBT-NS on all devices.
Segment the network to contain the attack.
Use strong passwords to reduce credential theft.
Monitor for spoofing or unusual traffic.
