1. A popular UNIX network protocol, RPC allows programs on one machine to make a "procedure" call on another machine. The upshot of this is that you could split a program in two halves, each part running on a separate machine. The procedure calls are invisibly mapped so that the programmer doesn't have to worry about the details. Contrast: The oldest form of RPC in use is Sun's RPC, upon which many famous protocols (such as NFS) are based. A newer form known as DCE RPC is used by Microsoft as the basis for its RPC services. The DCE version is dramatically more complex than the Sun variant, but supplies more services (such as built-in security). History: In the year 1999 (and early 2000), a wave of hacker attacks against Sun's RPC services swept the net. Virtually any Sun box connected to the net whose default RPC services were enabled, was hackable. Many Linux boxes were also hackable through RPC-based services. Virtually all of these attacks where through buffer overflow exploits. Example: Some RPC services are: portmapper Forms the core of the RPC system allowing a client to find servers. NFS This is the best known of all RPC services. Virtually all "file servers" use either Sun's NFS (in the UNIX world) or Microsoft's SMB (in the Windows world). Whenever one UNIX system is sharing a filesystem with another UNIX system, you can bet that they are using NFS. The name "NFS" means both the specific protocol called "NFS", but also the entire suite of supporting protocols like "mountd", "statd", and "lockd". rpc.mountd The "mount" sub-protocol of the NFS suite is used by a client to connect to the file service. It is named after the "mount" command in UNIX that is used to connect any filesystem into the main directory structure. This includes not only remote filesystems from NFS, but also floppy disks, CD-ROM drives, other partitions on the same hard-disk, or other hard-disks. Exploit: In 1998/1998 timeframe, a buffer-overflow in a Linux rpc.mountd implementation led to widespread compromises. See also: showmount rpc.statd Monitors the status of files; bugs in Linux and Solaris version have led to widespread exploits in 1998 through 2001. From Hacking-Lexicon