EternalBlue exploits a vulnerability in Microsoft's implementation of the Server Message Block (SMB) protocol. This vulnerability is denoted by entry CVE-2017-0144 in the Common Vulnerabilities and Exposures (CVE) catalog. The vulnerability exists because the SMB version 1 (SMBv1) server in various versions of Microsoft Windows mishandles specially crafted packets from remote attackers, allowing them to execute arbitrary code on the target computer.
In February 2018, EternalBlue was ported to all Windows operating systems since Windows 2000 by RiskSense security researcher Sean Dillon. EternalChampion and EternalRomance, two other exploits originally developed by the NSA and leaked by The Shadow Brokers, were also ported at the same event. They were made available as open sourced Metasploit modules.