What version of SMB did the WannaCry ransomware attack?

The WannaCry ransomware primarily exploited vulnerabilities in the SMB (Server Message Block)

version 1 protocol to propagate across network systems. Microsoft had identified vulnerabilities in

SMBv1, which were exploited by the EternalBlue exploit to spread the ransomware. This led to

widespread infections, particularly in systems that had not applied the security updates released to

patch the vulnerability.

Reference:

Microsoft Security Bulletin MS17-010, "Security Update for Microsoft Windows SMB Server".