On Friday and Saturday, a series of events unfolded that resulted in a 13-block chain reorganization on the Litecoin network, effectively reversing approximately 32 minutes of network activity. This was in response to a denial-of-service attack that exploited a vulnerability within the Mimblewimble Extension Block (MWEB) protocol, allowing invalid transactions to bypass nodes that had not been updated. The Litecoin Core v0.21.5.4 release, which includes crucial security updates, has been made available, and all users are advised to upgrade. 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 privately patched between March 19 and 26, roughly four weeks before the attack occurred. The consensus vulnerability was exploited to enable a denial-of-service attack against major mining pools, allowing invalid MWEB transactions to be processed before the network's longest valid chain corrected them. The attack was eventually mitigated when the network automatically handled the 13-block reorganization once the denial-of-service attack stopped, indicating that a sufficient amount of 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 being able to coordinate upgrades and push patches network-wide quickly, whereas older proof-of-work networks like Litecoin rely on independent mining pools to choose when to upgrade, creating a window of vulnerability when a security patch needs to be implemented. The Litecoin Foundation has not publicly addressed the GitHub timeline as of Sunday morning, and the amount of LTC pegged out during the invalid block window and the value of any swaps completed before the reorganization reversed them have not been disclosed.