Litecoin Recovers from Denial-of-Service Attack and 13-Block Rewrite

Late Friday and Saturday, a series of events unfolded on the Litecoin network, starting with a 13-block chain reorganization that reversed approximately 32 minutes of network activity. This reorganization was triggered by an attack exploiting a vulnerability in the Mimblewimble Extension Block (MWEB) protocol, which had been privately patched between March 19 and 26. The attackers utilized a denial-of-service attack against major mining pools, enabling invalid MWEB transactions to bypass nodes that had not been updated. The network's longest valid chain eventually corrected these transactions. In response, Litecoin Core v0.21.5.4 was released, containing crucial security updates, and all users were advised to upgrade. According to the Litecoin Foundation, the bug was fully patched, and the network resumed normal operation by Sunday morning. However, prominent researchers have pointed out discrepancies in the timeline of events, suggesting that the consensus vulnerability was known and patched privately a month before the attack. The vulnerability was exploited despite the patch being available, as it had not been publicly announced or mandated for all mining pools, creating a window of vulnerability. The attack has raised concerns about the differences in how various networks respond to exploits, with newer chains often coordinating upgrades more rapidly than older proof-of-work networks like Litecoin. The full extent of the damage, including the amount of LTC pegged out during the invalid block window and the value of any swaps completed before the reorganization, has not been disclosed.