Litecoin Network Recovers from Denial-of-Service Attack by Rewriting 13 Blocks

On Friday and Saturday, a series of events unfolded as a 13-block chain reorganization occurred on the Litecoin network, effectively reversing approximately 32 minutes of network activity. This reorganization was prompted by an attack exploiting a vulnerability within the Mimblewimble Extension Block (MWEB) protocol, allowing invalid transactions to temporarily bypass nodes that had not been updated. The Litecoin Core v0.21.5.4 release has been issued, advising all users to upgrade due to important security updates. According to the Litecoin Foundation, the bug has been fully patched and the network is now operating normally. However, security researchers have pointed out discrepancies in the timeline of events, suggesting that the vulnerability was known and patched privately between March 19 and 26, roughly four weeks before the attack. This has raised concerns regarding the window of vulnerability that existed between the private patch and the public release of the fix. The attack involved a denial-of-service component designed to take patched mining nodes offline, allowing unpatched nodes to form a chain that included invalid transactions. The automatic handling of the 13-block reorganization by the network once the denial-of-service attack stopped indicates that enough hashrate was running updated code to eventually overpower the attack. The incident highlights the differences in how various networks respond to exploits, with newer chains capable of coordinating upgrades quickly and older proof-of-work networks like Litecoin facing challenges due to independent mining pools choosing when to upgrade.