A chain reorganization of 13 blocks occurred on LTC at $54.99 late Friday and Saturday, undoing approximately 32 minutes of network activity after attackers exploited a vulnerability in the Mimblewimble Extension Block (MWEB) protocol. The bug had enabled a denial-of-service attack against major mining pools, allowing invalid MWEB transactions to bypass nodes that had not been updated before the network's longest valid chain corrected them. A new version of Litecoin Core, v0.21.5.4, has been released, and all users are advised to upgrade due to important security updates. According to the Litecoin Foundation, the bug was fully patched and the network is now operating normally by Sunday morning.
However, prominent researchers claim that the timeline of events, as shown on the litecoin-project GitHub repository, tells a different story. The vulnerability that allowed the invalid MWEB peg-out was privately patched between March 19 and March 26, roughly four weeks before the attack, and a separate denial-of-service vulnerability was patched on the morning of April 25.
Both fixes were included in the release 0.21.5.4 the same afternoon, after the attack had already begun. The fact that the vulnerability was known and patched a month before the exploit but not publicly disclosed or required for all mining pools created a window of opportunity for the attackers.
The attackers appeared to have knowledge of which miners were running the patched code and which were still vulnerable. Blockchain data revealed that the attacker had pre-funded a wallet 38 hours before the exploit through a Binance withdrawal, with the destination address already configured to swap LTC into ETH on a decentralized exchange.
The denial-of-service attack and the MWEB bug were separate components, with the DoS designed to take patched mining nodes offline so the unpatched ones would form the chain that included the invalid transactions. The network's ability to automatically handle the 13-block reorganization once the DoS stopped suggests that enough hashrate was running updated code to eventually overpower the attack, but only after the unpatched fork had run for 32 minutes.
This incident highlights the differences in how code maintainers and developers react to exploits on various networks. Newer chains with smaller, more centralized validator sets can coordinate upgrades and push patches network-wide in hours, whereas older proof-of-work networks like Litecoin and bitcoin rely on independent mining pools choosing when to upgrade, creating a window of vulnerability when a security patch needs to reach everyone before an attacker exploits the gap.