August 26, 2021

Responder & NTLMRelayx

The documentation for Responder suggests that using the *-r* and -*d* may “…likely break stuff on the network”. However, I can’t find any information on why this would be or how to safely use it. In my lab, I’ve been able to successfully use Responder and pass hashes to ntlmrelayx, which has granted me *system* privileges on the target test machine. However, it’s my understanding in order to relay those hashes to something like ntlmrelayx, I need to use the -r and -d flag (which could break stuff).

I’m concerned about enabling these flags since I can’t find an explanation of WHY this is dangerous and how it could break the network. Is this an overstatement of breaking the entire network? Or is it suggesting it could impact the specific user(s) hashes are being captured and relayed for? For example, would/could running *responder -I etho -r -d* cause a disruption to SMB and/or other network services?

Again, I’ve successfully used responder and ntlmrelayx in the lab and to my knowledge haven’t broken anything. I don’t know if this is because I’ve just gotten lucky, nobody has reported an interruption of services, or it only effects my test accounts. Any insight would be greatly appreciated. Thanks in advance.

PS: I’m questioning this because as an IT Consultant I’m concerned about running this scenario in a production environment with many users and possibly causing a service interruption. I’d feel much more comfortable if I better understood how/why/when using -r and -d could “…break the network”.



I assume this is why.

This tool is first an LLMNR and NBT-NS responder, it will answer to *specific* NBT-NS (NetBIOS Name Service) queries based on their name suffix (see: By default, the tool will only answers 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.

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