The Bitcoin Core Project released Bitcoin Core 0.16.3, an update designed to fix a severe denial-of-service vulnerability which would allow any miner on the Bitcoin network to bring down vulnerable Bitcoin nodes via duplicate input.
Although the bug did not affect the Bitcoin protocol per se, it did affect all cryptocurrencies built using the Bitcoin Core node software designed to provides bitcoin wallets which thoroughly verify payments.
As advised in the release notes published by the Bitcoin Core developers, all nodes need to be upgraded to the new version by shutting them down and reinstalling using the platform-specific procedure.
The denial-of-service (DoS) vulnerability assigned as CVE-2018-17144 in the security vulnerability database, would allow an attacker, in this case, any miner on the network, to cause a remote denial of service, crashing any vulnerable nodes and disconnecting the network.
Moreover, the would happen when nodes would try to validate a block containing transactions which attempted to spend the same amount of coin twice.
Attackers willing to lose $80,000 could have brought down part of the Bitcoin network
Fortunately, the malicious invalid blocks can be created only by miners who would be capable of producing a sufficient Proof-of-Work (PoW) block and were also willing to lose the generated income (at least $80,000 or 12.5 XBT).
The node attackers prepared to lose that amount of money would have been able to crash the bitcoind program (or its GUI-based counterpart Bitcoin-Qt) running on the node and designed to implement the Bitcoin protocol for RPC (remote procedure call) use.
An attacker who would have been ready to lose money to bring down part of the network (or at least an essential chunk of it) would have probably been successful if the Bitcoin Core devs wouldn't have released the patched version so quickly and distributed it to all node owners for quicky patching.
This is not the first serious vulnerability found to affect the Bitcoin network, a list of all of them with detailed descriptions is available on bitcoin.it's Common Vulnerabilities and Exposures page.