Litecoin Network Subjected to Denial-of-Service Attack, Prompting 13-Block Rewrite

On Friday and Saturday, a chain reorganization of 13 blocks on the Litecoin network reversed approximately 32 minutes of network activity after attackers exploited a vulnerability in the Mimblewimble Extension Block protocol. The bug allowed for a denial-of-service attack against major mining pools, enabling invalid transactions to bypass nodes that had not been updated before the network's longest valid chain corrected them. Litecoin Core version 0.21.5.4 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 operating normally as of Sunday morning. However, security researchers have pointed out that the litecoin-project GitHub repository reveals a different timeline. The consensus vulnerability was privately patched between March 19 and March 26, roughly four weeks before the attack, while a separate denial-of-service vulnerability was patched on the morning of April 25.

Both fixes were included in release 0.21.5.4 the same afternoon, after the attack had 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.

Blockchain data showed that the attacker pre-funded a wallet 38 hours before the exploit and had configured the destination address to swap LTC for 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, allowing the unpatched ones to form the chain that included the invalid transactions. The network's automatic handling of the 13-block reorganization once the DoS stopped suggests that enough hashrate was running updated code to eventually overpower the attack. The incident highlights the differences in how code maintainers and developers react to exploits on various networks.

Older proof-of-work networks like Litecoin and Bitcoin rely on independent mining pools choosing when to upgrade, which can create a window of vulnerability when a security patch needs to reach everyone before an attacker exploits the gap.