Researchers from the University of Illinois reported that the Lightning Network is potentially vulnerable to a zombie attack and a coordinated double-spend attack.
Cosimo Sguanci and Anastasios Sidiropoulos of the University of Illinois have discovered a vulnerability in the Layer 2 solution for Bitcoin’s Lightning Network. They published an article describing a hypothetical attack based on the collusion of node operators, during which a coalition of 30 nodes can steal 750 BTC ($17 million).
The experts added that attackers will be able to control a certain number of nodes and disable channels using a zombie attack. A zombie attack occurs when multiple nodes become unresponsive, locking up assets in any channel connected to those nodes.
To protect against a zombie attack, honest nodes must close their channels and leave the Lightning Network. This requires high transaction fees, renders the Lightning Network channels unusable, and overloads the Bitcoin network. Thus, a massive double-spend attack will be more profitable than a “zombie” attack.
According to experts, attackers can conspire with several dozen large nodes and overload the Bitcoin network, sending a stream of fraudulent transactions to close a large number of Lightning Network channels. If attackers pay a high fee and move forward in line, they can spend bitcoins twice.
Experts believe that honest nodes will be able to protect themselves from a massive double-spend attack by sending so-called “justice transactions”, challenging fraudulent requests to close the channel. During the attack, attackers will compete with honest nodes in persuading miners to enable fraudulent transactions before honest transactions.
If honest nodes cannot pay miners enough to enable their transactions, the attackers will win. The researchers suggested that as a defense against a double-spend attack, increase the “to_safe_delay” variable, which adds an additional cost for a longer wait if the user decides to close the channel without any response from his counterparty.
Recall that in March, the number of bitcoins blocked in the Lightning Network exceeded 3,500 BTC.
Source: Bits
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