Late Friday and Saturday, a series of events unfolded on the Litecoin network, culminating in a 13-block chain reorganization that rewound approximately 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, enabling the attackers to push through invalid transactions on unupdated nodes before the network self-corrected. The Litecoin Core v0.21.5.4 update, released subsequently, contains crucial security patches and is strongly advised for all users.
According to the Litecoin Foundation, the bug has been fully patched, and normal network operations have resumed. However, security researchers have pointed out discrepancies between the foundation's account and the timeline of events as recorded on the litecoin-project GitHub repository. It appears the consensus vulnerability was known and privately patched between March 19 and 26, more than four weeks before the attack occurred.
A separate denial-of-service vulnerability was addressed on April 25, with both fixes being incorporated into the v0.21.5.4 release after the attack had begun. The term 'zero-day' typically refers to a vulnerability that is unknown to the defenders at the time of the attack, but in this case, the vulnerability was known and patched, albeit not publicly disclosed or mandatory for all mining pools at the time of the attack.
This created a window of opportunity for attackers, who seemed to be aware of which miners were running the patched code and which were still vulnerable. Concerns have been raised by experts, including Alex Shevchenko, CTO of NEAR Foundation's Aurora project, who highlighted the pre-funding of a wallet 38 hours before the exploit and the attacker's apparent plan to swap LTC for ETH on a decentralized exchange. The attack and the MWEB bug are seen as separate but coordinated components, with the denial-of-service attack designed to take patched mining nodes offline, allowing the unpatched nodes to validate the chain with the invalid transactions. The network's automatic handling of the 13-block reorganization once the denial-of-service attack stopped suggests that enough mining power was running the updated code to eventually overpower the attack.
This incident highlights the differences in how various blockchain networks respond to exploits, with newer chains often able to coordinate upgrades more swiftly due to their smaller, more centralized validator sets, in contrast to older proof-of-work networks like Litecoin and Bitcoin, which rely on independent mining pools to choose when to upgrade, creating potential windows of vulnerability.