Funds of intermediate hops can be forcefully locked up for a long time.

[joostjager]

Background

It seems a route can be crafted that forces intermediate hops to lock up their funds for a long time by intentionally black-holing the payment. It does require the attacker to lock up funds too, but the cost for this may be lower for the attacker than for the target.

Your environment

• lnd e5b84cf
• Ubuntu linux
• btcd

Steps to reproduce

• Modify lnd of Charlie to represent finalCLTVDelta as uint32 in newRoute (instead of the current uint16) and force it to 1000000 blocks.
• Set exit settle hodl flag on Alice
• Send payment from Charlie via Bob to Alice. Bob is the unaware intermediary.

Expected behaviour

Bob doesn't like such a long time lock and refuses the htlc.

Actual behaviour

Bob commits to the HTLC and needs to wait 1000000 blocks to get his money back.

  "pending_htlcs": [
                {
                    "incoming": true,
                    "amount": "6001",
                    "hash_lock": "DUNVXFiMBW58rh8sEEL/HI1vg6YdndMrfxjarudlATY=",
                    "expiration_height": 1007324
                }