The WannaCry ransomware program is not that special or sophisticated. It exploits a critical remote code execution vulnerability in the Windows implementation of the Server Message Block 1.0 (SMBv1) protocol. Microsoft released a patch for this vulnerability in March and, on the heels of the attack Friday, even took the unusual step of releasing fixes for older versions of Windows that are no longer supported, such as Windows XP, Windows Server 2013, and Windows 8. Security vendors are still seeing successful exploitation attempts today for MS08-067, the vulnerability that allowed Conficker computer worm to spread nine years ago.”]
Source: https://www.csoonline.com/article/3196985/wannacry-attacks-are-only-the-beginning.html