Litecoin Recovers from Denial-of-Service Attack That Rolled Back 13 Blocks

On Friday and Saturday, a series of events unfolded as a 13-block chain reorganization occurred on the Litecoin network, effectively rewinding 32 minutes of activity. This was in response to a denial-of-service attack that targeted major mining pools, leveraging a vulnerability within the Mimblewimble Extension Block (MWEB) protocol. The exploit allowed invalid MWEB transactions to bypass nodes that had not been updated, before the network's longest valid chain intervened to correct them.

Following the incident, Litecoin Core v0.21.5.4 was released, containing crucial security updates and advising all users to upgrade. According to the Litecoin Foundation, the bug was fully patched, and the network resumed normal operations by Sunday morning. However, security researchers have pointed out discrepancies in the timeline of events, suggesting that the vulnerability was known and privately patched between March 19 and 26, roughly four weeks before the attack.

The consensus vulnerability was patched, but the fix was not publicly broadcasted or mandated for all mining pools, creating a window of vulnerability. This allowed attackers to target unpatched nodes, while others ran the updated code. The attack involved a pre-funded wallet, which was used to swap LTC for ETH on a decentralized exchange.

The denial-of-service attack and MWEB bug were separate components, designed to take patched mining nodes offline and include invalid transactions in the chain. The network's automatic handling of the 13-block reorganization, once the DoS stopped, indicates that sufficient hashrate was running updated code to overpower the attack. The incident highlights the differences in how various networks respond to exploits, with newer chains having more centralized validator sets and older proof-of-work networks relying on independent mining pools.

The Litecoin Foundation has not publicly addressed the GitHub timeline, and the amount of LTC pegged out during the invalid block window and the value of any swaps completed before the reorganization remain undisclosed.