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 network activity. This was in response to a denial-of-service attack that leveraged a vulnerability in 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 has been issued, containing crucial security updates, 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. This has raised concerns about the window of vulnerability that existed due to the private patching and the lack of public disclosure or mandatory updates for mining pools.
The attack involved a separate denial-of-service vulnerability that was patched on April 25, with both fixes being rolled into the release 0.21.5.4 after the attack had begun. The fact that the network automatically handled the 13-block reorganization once the DoS stopped suggests that enough hashrate was running updated code to eventually overpower the attack.
This incident highlights the differences in how various networks respond to exploits, with newer chains having more centralized validator sets and the ability to push patches network-wide quickly, whereas older proof-of-work networks like Litecoin rely on independent mining pools choosing when to upgrade, creating a window of vulnerability.