wtclientrpc: prevent watchtower connections to local addresses by anibilthare · Pull Request #9230 · lightningnetwork/lnd

anibilthare · 2024-10-29T07:39:19Z

Change Description

Fixes 5522

Adds validation to prevent watchtower client connections to local addresses by:

Implementing IsLocalAddress() to detect localhost/local network addresses
Adding check in AddTower RPC to reject local tower connections
Including unit tests for address validation

This helps prevent security issues from misconfigured watchtower setups that accidentally expose local addresses.

Steps to Test

Steps for reviewers to follow to test the change.

Adds validation to prevent watchtower client connections to local addresses by: - Implementing IsLocalAddress() to detect localhost/local network addresses - Adding check in AddTower RPC to reject local tower connections - Including comprehensive unit tests for address validation This helps prevent security issues from misconfigured watchtower setups that accidentally expose local addresses.

coderabbitai · 2024-10-29T07:39:28Z

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anibilthare · 2024-10-29T07:44:36Z

@ellemouton Please review.

ellemouton · 2024-10-29T07:45:31Z

@anibilthare - I think the issue was more about connecting to your own watchtower on the same LND node. ie, connecting the wtclient to the watchtower server on the same LND node

anibilthare · 2024-10-29T07:58:32Z

Thanks for the quick response @ellemouton !!

I chose to check for all local addresses (rather than just same-node) for these reasons:

Security: Running multiple LND nodes on the same machine means they share the same failure domain - if the machine is compromised, all nodes including their watchtowers are compromised
Redundancy: The purpose of watchtowers is to provide backup/monitoring from an independent system. Having the watchtower on the same physical machine defeats this purpose since any hardware/system failure would affect both the node and its watchtower
Practical Implementation: Detecting "same LND node" would require comparing node identities, while checking local addresses provides a robust way to prevent all potentially problematic local configurations
Future-proofing: This approach also prevents users from accidentally creating other insecure local watchtower setups as they experiment with different configurations

Would you prefer we narrow the scope to only prevent same-node connections? I'm open to adjusting the approach if you think the current implementation is too broad.

anibilthare · 2024-11-02T03:44:08Z

@ellemouton Any feedback ?

ellemouton · 2024-11-05T05:37:25Z

@anibilthare - my concern is that this makes testing hard/impossible. We could just log a warning instead? Your points are all valid but i think the user should have the flexibility to run things how they want to & they themselves should be aware of the risks of certain run configurations

imo, the original issue isnt really an issue anyways... maybe others disagree.

GustavoStingelin · 2025-02-28T02:24:31Z

@anibilthare - my concern is that this makes testing hard/impossible. We could just log a warning instead? Your points are all valid but i think the user should have the flexibility to run things how they want to & they themselves should be aware of the risks of certain run configurations

imo, the original issue isnt really an issue anyways... maybe others disagree.

Agreed, a warning log is a good starting point.

GustavoStingelin · 2025-02-28T02:33:15Z

What happens if a public IP is configured to point to the same node? The local interface IP will never be the public IP, so I’m not sure this solution would work in that case. If it does, how can we test it? Also, what about onion addresses?

mapaba79

Hi @anibilthare, thanks for the PR! The implementation is clean and the unit tests are well-structured.

However, I agree with the previous feedback that a hard rejection for all local addresses might be too restrictive, especially for integration testing.

I suggest replacing the connection rejection with a log.Warnf. This informs the user about the redundancy risks without breaking valid local setups or stripping away their flexibility. What do you think?

mapaba79 · 2026-02-27T20:35:07Z

 			err)
 	}

+	if lncfg.IsLocalAddress(addr) {


Consider replacing this hard error with a log.Warnf. This prevents breaking integration tests or specific local setups while still fulfilling the goal of alerting the user about the lack of redundancy.

lightninglabs-deploy · 2026-06-01T05:24:22Z

@anibilthare, remember to re-request review from reviewers when ready

guggero added the good first review Pull Requests that are suitable for new contributors that want to learn code review label Mar 28, 2025

mapaba79 suggested changes Feb 27, 2026

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anibilthare commented Oct 29, 2024

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