rexecd(8) - NetBSD Manual Pages

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REXECD(8)               NetBSD System Manager's Manual               REXECD(8)


NAME

     rexecd - remote execution server


SYNOPSIS

     rexecd


DESCRIPTION

     rexecd is the server for the rexec(3) routine.  The server provides re-
     mote execution facilities with authentication based on user names and
     passwords.

     rexecd listens for service requests at the port indicated in the ``exec''
     service specification; see services(5).  When a service request is re-
     ceived the following protocol is initiated:

     1.   The server reads characters from the socket up to a NUL (`\0') byte.
          The resultant string is interpreted as an ASCII number, base 10.

     2.   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.

     3.   A NUL terminated user name of at most 16 characters is retrieved on
          the initial socket.

     4.   A NUL terminated, unencrypted password of at most 16 characters is
          retrieved on the initial socket.

     5.   A NUL 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.

     6.   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 mes-
          sage returned.

     7.   A NUL byte is returned on the initial socket and the command line is
          passed to the normal login shell of the user.  The shell inherits
          the network connections established by rexecd.


DIAGNOSTICS

     Except for the last one listed below, all diagnostic messages are re-
     turned on the initial socket, after which any network connections are
     closed.  An error is indicated by a leading byte with a value of 1 (0 is
     returned in step 7 above upon successful completion of all the steps pri-
     or 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(2) to the home directory failed.

     Try again.
             A fork(2) by the server failed.

     <shellname>: ...
             The user's login shell could not be started.  This message is re-
             turned on the connection associated with the stderr, and is not
             preceded by a flag byte.


SEE ALSO

     rexec(3)


BUGS

     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 and password exchanges to be encrypted
     should be present.


HISTORY

     The rexecd command appeared in 4.2BSD.


SECURITY CONSIDERATIONS

     As the passwords exchanged by the client and rexecd are not encrypted, it
     is strongly recommended that this service is not enabled.

NetBSD 1.5.2                     June 1, 1994                                2