rexecd(1Mtcp)

rexecd -- remote execution server

Synopsis

in.rexecd host.port

Description

The rexecd command is the server for the rexec(3N) routine. The server provides remote execution facilities with authentication based on user names and encrypted passwords.

Diagnostics

All diagnostic messages are returned on the connection associated with the stderr, after which any network connections are closed. An error is indicated by a leading byte with a value of 1; the value 0 is returned in step 7 below upon successful completion of all the steps prior to the command execution.

username too long: The name is longer than 16 characters.
password too long: The password is longer than 16 characters.
command too long: The command line passed exceeds the size of the argument list (as configured into the system).
Login incorrect.: No password file entry for the user name existed.
Password incorrect.: The wrong password was supplied.
No remote directory.: The chdir command to the home directory failed.
Try again.: A fork by the server failed.
/usr/bin/sh: ...: The user's login shell could not be started.

Usage

rexecd is invoked automatically as needed by inetd(1Mtcp), and then executes the following protocol:

The server reads characters from the socket up to a null (\0) byte. The resultant string is interpreted as an ASCII number, base 10.
If the number received in step 1 is non-zero, it is interpreted as the port number of a secondary stream to be used for the stderr. A second connection is then created to the specified port on the client's machine.
A null terminated user name of at most 16 characters is retrieved on the initial socket.
A null terminated, encrypted, password of at most 16 characters is retrieved on the initial socket.
A null terminated command to be passed to a shell is retrieved on the initial socket. The length of the command is limited by the upper bound on the size of the system's argument list.
rexecd then validates the user as is done at login time and, if the authentication was successful, changes to the user's home directory, and establishes the user and group protections of the user. If any of these steps fail the connection is aborted with a diagnostic message returned.
A null byte is returned on the connection associated with the stderr and the command line is passed to the normal login shell of the user. The shell inherits the network connections established by rexecd.

References

inetd(1Mtcp)

Notices

Indicating Login incorrect as opposed to Password incorrect is a security breach which allows people to probe a system for users with null passwords.

A facility to allow all data exchanges to be encrypted should be present.