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

Late Friday and Saturday, a series of events unfolded on the Litecoin network, culminating in a 13-block reorganization to undo the effects of a denial-of-service attack that took advantage of a vulnerability in the Mimblewimble Extension Block (MWEB) protocol. This vulnerability had been privately patched between March 19 and 26 but had not been publicly disclosed or mandatory for all mining pools to update, creating a window of vulnerability. Attackers exploited this gap, using the vulnerability to slip invalid MWEB transactions through nodes that hadn't updated, before the network's longest valid chain corrected them. Following the attack, Litecoin Core version 0.21.5.4 was released, containing critical security updates and advising all users to upgrade. According to the Litecoin Foundation, the bug was fully patched, and the network is now operating normally. However, security researchers have pointed out discrepancies between the foundation's account and the timeline of patches on the Litecoin GitHub repository. The repository shows that the consensus vulnerability was known and patched a month before the attack but was not made public or mandated for mining pools, allowing attackers to target unpatched nodes. The attack and subsequent response have raised questions about the handling of vulnerabilities and patches in cryptocurrency networks, particularly in proof-of-work systems like Litecoin and Bitcoin, where independent mining pools can delay upgrades and create windows of vulnerability.