Practical UNIX and Internet Security, 3rd Edition

Understanding SMB

The Server Message Block (SMB) protocol is the standard DOS and Windows approach to network file and printer sharing. SMB is a client/server protocol that provides a mechanism for clients to access server filesystems (as well as printers and other input/output abstractions).

What’s SMB doing in a book about Unix security? Although many sites run networks composed entirely of Unix workstations and servers, heterogeneous networks that contain both Windows-based and Unix-based hosts have become very common. Thanks to Samba, the free Unix implementation of the SMB protocol, Unix systems can participate in SMB networks as either clients or servers, and in this section we focus on the security implications of this participation for those Unix hosts.

Solaris offers support for SMB using its Solstice PC-NetLink product, whereas Mac OS Version 10.2 and above include native support for SMB.

SMB History

The SMB protocol has been in use since the mid 1980s, and has gone through several major revisions. It was available for DOS-based PCs in the form of LAN Manager, and was broadly introduced in Microsoft Windows for Workgroups 3.11. The early versions of SMB provided a useful, if relatively unsecure, peer-to-peer file-sharing system.

Later protocol dialects, introduced with Windows 95, Windows 98, and Windows NT (and present in even later versions of Windows, including XP), provided several security improvements. SMB clients and servers negotiate with one another to determine ...