Bitcoin Core version 0.16.3 is now available for download with a fix for a denial-of-service vulnerability introduced in Bitcoin Core 0.14.0 and affecting all subsequent versions though to 0.16.2. We highly recommend users of all affected versions immediately upgrade to 0.16.3.
Security issue CVE-2018-17144: it was discovered that older versions of Bitcoin Core will crash if they try to process a block containing a transaction that attempts to spend the same input twice. Such blocks are invalid, so they can only be created by a miner willing to sacrifice their allowed income for creating a block of at least 12.5 BTC (about $80,000 USD as of this writing). This release eliminates the crash, allowing the software to quietly reject such invalid blocks.