The SMB client in Microsoft Windows Server 2008 R2 and Windows 7 does not properly handle (1) SMBv1 and (2) SMBv2 response packets, which allows remote SMB servers and man-in-the-middle attackers to execute arbitrary code via a crafted packet that causes the client to read the entirety of the response, and then improperly interact with the Winsock Kernel (WSK), aka "SMB Client Message Size Vulnerability."