Litecoin Network Faces Denial-of-Service Attack, Successfully Reverses Effects with 13-Block Rewind

Late Friday and Saturday, a series of events unfolded as a 13-block chain reorganization on the Litecoin network rewound approximately 32 minutes of network activity. This action was taken 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, advising all users to upgrade due to important security updates.

According to the Litecoin Foundation, the bug was fully patched, and the network is now operating as normal. However, security researchers have pointed out discrepancies in the timeline of events, suggesting that the consensus vulnerability was privately patched between March 19 and 26, roughly four weeks before the attack occurred.

The patch for a separate denial-of-service vulnerability was applied on the morning of April 25, with both fixes being included in the release 0.21.5.4 the same afternoon, after the attack had begun. This sequence of events has raised concerns among researchers, who argue that the attack was not a zero-day exploit, as the vulnerability was known and patched a month prior. The exploit appears to have been designed to take advantage of the window between the private patch and its public release, targeting mining pools that had not yet updated their code. Blockchain data indicates that the attacker had pre-funded a wallet 38 hours before the exploit, with plans to swap the stolen LTC for ETH on a decentralized exchange.

The automatic handling of the 13-block reorganization by the network, once the denial-of-service attack stopped, suggests that a sufficient amount of hashrate was running the updated code, eventually overpowering the attack. This incident highlights the differences in how various networks respond to exploits, with newer chains often coordinating upgrades more quickly and older proof-of-work networks like Litecoin facing challenges in pushing security patches to all independent mining pools in a timely manner.