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1 .TH scponly 8 "Sept 04, 2002" ""
2 .SH NAME
4 .SH SYNOPSIS
6 \- limited shell for secure file transfers
7 .SH DESCRIPTION
9 is an alternative "shell" (of sorts) for system administrators who would like
10 to provide access to remote users to both read and write local files without
11 providing any remote execution privileges. Functionally, it is best described
12 as a wrapper to the trusted suite of ssh applications.
14 A typical usage of
16 is in creating a semi-public account not unlike the concept of anonymous login
17 for ftp. This allows an administrator to share files in the same way an
18 anonymous ftp setup would, only employing all the protection that ssh provides.
19 This is especially significant if you consider that ftp authentications
20 traverse public networks in a plaintext format.
22 Instead of just a single anonymous user,
24 supports configuring potentially many users, each of which could be set
25 up to provide access to distinct directory trees. Aside from the installation
26 details, each of these users would have their default shell in /etc/passwd set
27 to "/usr/local/bin/scponly" (or wherever you choose to install it). This
28 would mean users with this shell can neither login interactively or execute
29 commands remotely. They can however, scp files in and out, governed by the
30 usual Unixish file permissions.
31 .SH FEATURES
32 .IP \(bu
35 logs time, client IP address, username, and the actual request to syslog.
36 .IP \(bu
39 can chroot to the user's home directory (or any other directory the user has
40 permissions for), disallowing access to the rest of the filesystem.
41 .IP \(bu
42 sftp compatibility:
44 is fully compatible with sftp.
45 .IP \(bu
46 Security checks: root login is disallowed, seteuid after chroot.
47 .IP \(bu
48 WinSCP compatibility:
50 can be compiled in WinSCP compatibility mode that will permit a
51 "semi-interactive" shell that WinSCP can use.
52 .IP \(bu
53 gftp compatibility.
54 \fBscponly\fP is also fully compatible with gFTP in sftp mode.
57 doesn't do anything to manage read/write permissions. The ssh applications
58 already do that just fine. If you use
60 be aware that good old Unix-style file permissions are still doing the work of
61 protecting your files.
62 .SH NOTES
63 .IP \(bu
64 As recent as June 26, 2002, vulnerabilities have been
65 discovered in OpenSSH. There is also a SSH1 protocol vulnerability. If
66 you're going to use
68 , be aware it is no more secure than the ssh installation it runs on.
69 .IP \(bu
70 I've since discovered that ssh.com's commercial ssh offering supports BOTH
71 "dummy users" as well as functionality paralleling
73 I have not been able to find any notes on these features, but I did read that
74 they exist. I will make a point to include more information later. It appears
75 that OpenSSH does not yet support these features. At this time, I have no
76 plans to end-of-life
78 though ultimately, I recognize that
80 should eventually become just a feature of whichever sshd you may run.
81 .SH FILES
83 .B /usr/local/bin/scponly
84 The default location for the shell itself.
86 .B /usr/local/sbin/scponlyc
87 The default location for the chrooted version.
89 .B /etc/shells
90 To be a proper shell, it has to be included here.
91 .SH SEE ALSO
98 .SH AUTHORS
99 An Joe Boyle Aq firstname.lastname@example.org .
100 .SH LEGALITIES
101 Copyright (C) 2001, 2002, 2003
102 An Joe Boyle Aq email@example.com .
104 Redistribution and use in source and binary forms, with or without
105 modification, are permitted provided that the following conditions are met:
107 1. Redistributions of source code must retain the above copyright notice, this
108 list of conditions and the following disclaimer.
110 2. Redistributions in binary form must reproduce the above copyright notice,
111 this list of conditions and the following disclaimer in the documentation
112 and/or other materials provided with the distribution.
114 THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
115 WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
116 MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
117 EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
118 EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
119 OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
120 INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
121 CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
122 IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
123 OF SUCH DAMAGE.
124 .SH BUGS
125 Versions prior to 2.4 were susceptible to shell circumvention via the
126 $HOME/.ssh/environment file which allowed perversion of LD_LIBRARY_PATH and PATH
127 environment variables.