1.\" $NetBSD: rexecd.8,v 1.13 2017/07/03 21:35:49 wiz Exp $ 2.\" 3.\" Copyright (c) 1983, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" from: @(#)rexecd.8 8.3 (Berkeley) 6/1/94 31.\" 32.Dd June 1, 1994 33.Dt REXECD 8 34.Os 35.Sh NAME 36.Nm rexecd 37.Nd remote execution server 38.Sh SYNOPSIS 39.Nm 40.Sh DESCRIPTION 41.Nm 42is the server for the 43.Xr rexec 3 44routine. 45The server provides remote execution facilities with authentication 46based on user names and passwords. 47.Pp 48.Nm 49listens for service requests at the port indicated in 50the ``exec'' service specification; see 51.Xr services 5 . 52When a service request is received the following protocol 53is initiated: 54.Bl -enum 55.It 56The server reads characters from the socket up to a NUL 57.Pq Ql \e0 58byte. 59The resultant string is interpreted as an 60.Tn ASCII 61number, base 10. 62.It 63If the number received in step 1 is non-zero, 64it is interpreted as the port number of a secondary 65stream to be used for the 66.Em stderr . 67A second connection is then created to the specified 68port on the client's machine. 69.It 70A NUL terminated user name of at most 16 characters 71is retrieved on the initial socket. 72.It 73A NUL terminated, unencrypted password of at most 7416 characters is retrieved on the initial socket. 75.It 76A NUL terminated command to be passed to a 77shell is retrieved on the initial socket. 78The length of the command is limited by the upper bound on the size 79of the system's argument list. 80.It 81.Nm 82then validates the user as is done at login time and, if the 83authentication was successful, changes to the user's home directory, 84and establishes the user and group protections of the user. 85If any of these steps fail the connection is 86aborted with a diagnostic message returned. 87.It 88A NUL byte is returned on the initial socket and the command line 89is passed to the normal login shell of the user. 90The shell inherits the network connections established by 91.Nm . 92.El 93.Sh DIAGNOSTICS 94Except for the last one listed below, 95all diagnostic messages are returned on the initial socket, 96after which any network connections are closed. 97An error is indicated by a leading byte with a value of 981 (0 is returned in step 7 above upon successful completion 99of all the steps prior to the command execution). 100.Pp 101.Bl -tag -width Ds 102.It Sy username too long 103The name is 104longer than 16 characters. 105.It Sy password too long 106The password is longer than 16 characters. 107.It Sy command too long 108The command line passed exceeds the size of the argument 109list (as configured into the system). 110.It Sy Login incorrect. 111No password file entry for the user name existed. 112.It Sy Password incorrect. 113The wrong password was supplied. 114.It Sy \&No remote directory. 115The 116.Xr chdir 2 117to the home directory failed. 118.It Sy Try again. 119A 120.Xr fork 2 121by the server failed. 122.It Sy <shellname>: ... 123The user's login shell could not be started. 124This message is returned 125on the connection associated with the 126.Em stderr , 127and is not preceded by a flag byte. 128.El 129.Sh SEE ALSO 130.Xr rexec 3 131.Sh HISTORY 132The 133.Nm 134command appeared in 135.Bx 4.2 . 136.Sh BUGS 137Indicating ``Login incorrect'' as opposed to ``Password incorrect'' 138is a security breach which allows people to probe a system for users 139with null passwords. 140.Pp 141A facility to allow all data and password exchanges to be encrypted should be 142present. 143.Sh SECURITY CONSIDERATIONS 144As the passwords exchanged by the client and 145.Nm 146are not encrypted, it is 147.Em strongly 148recommended that this service is not enabled. 149