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.