If you only ever want the user account to perform the one function, override their system shell.

example:
oper:x:519:519::/home/oper:/usr/local/bin/oper-only-ever-gets-to-do-this
.sh

Regardless of how the account logs in, telnet, ssh, &c they'll only execute that one thing.

________________________________________
From: listbounce (at) securityfocus (dot) com [email concealed] [listbounce (at) securityfocus (dot) com [email concealed]] On Behalf Of Walter de Jong [walter (at) sara (dot) nl [email concealed]]
Sent: Tuesday, April 19, 2011 8:23 AM
To: secureshell (at) securityfocus (dot) com [email concealed]
Subject: ForceCommand executes shell

Hi,

I have set up a sshd_config that uses an alternate port number and
ForceCommand to force the execution of a home-made service to our users.

ForceCommand executes the command using 'shell' '-c', and as a result
the user's .bashrc, .tcshrc, .whateverrc is being loaded -- which is
something I was trying to prevent, because I'm trying to "force a
command" upon them. In my case loading a .bashrc can be considered as a
security hole.

Is there any way around this? Maybe a different kind of setup would be
better?
I like using ssh for the service because of its excellent authentication
mechanisms.

I even made a patch to sshd session.c (see below) but I'd rather not
have to maintain local mods to the source.

Greets,

--Walter

void do_child()

/*
argv[0] = (char *) shell0;
argv[1] = "-c";
argv[2] = (char *) command;
argv[3] = NULL;
*/
argv[0] = "/bin/bash";
argv[1] = "--norc";
argv[2] = "--noprofile";
argv[3] = "-c";
argv[4] = (char *)command;
argv[5] = NULL;

execve(shell, argv, env);
perror(shell);
exit(1);

--
*** If you build it, they will come ***

HPC Systems Programmer at SARA Computing and Network Services
People should be able to e-mail me, spambots should not.

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