This problem is actually caused by a missing specification in BIP144 to put some kind of a reasonable limit on the size of transaction witness data.
By my estimation, with a ~$600 fee, and a 127999 of 128000 a person can delay all transaction processing by one block.
This could be used in addition to a DoS attack on a channel counterpart to perform a sniper attack on a channel in the last hour of its HTLC timeout. It would start to become economic somewhere around channel size of 0.5 BTC.
Interesting approach to this attack vector. We are in the Lightning Network´s infancy, we take advantage of the same network that has allowed Visa and Mastercard to monopolize payments and thus we are subject to some attacks as well. We should be keeping an eye and testing as much as possible.
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The only thing to be done about it at this point is simply use small channels that can't be economically attacked. Putting a really big fee on the closure transaction would also possibly give a strong chance of displacing the giant tx.
I'm sure some kind of countermeasure will be devised in the future but for now best to just keep channels small like no bigger than 0.5btc maybe, if you aren't very sure about your counterparty, 0.1. In any case, more links are better so 10 0.1btc channels is probably better for the network than 2 at 0.5.
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