zen-parsegmx.net wrote:

> If the user has local access to the system, it is possible to get the
> program to set arbitrary environment variables in the environment of
> /bin/login. e.g. LD_PRELOAD=/tmp/make-rootshell.so

To protect against this (and possible bad environment processing within
telnetd itself), create some otherwise unused group and make /bin/login
setgid to that:

# chown root._login_ /bin/login
# chmod 6711 /bin/login
# ls -l /bin/login
-rws--s--x 1 root _login_ 24752 Aug 25 2000 /bin/login

(Since telnetd runs as root, login has getuid==geteuid so the OS may follow
LD_PRELOAD and similar variables. Using this login has getgid!=getegid and
the OS should disallow such trickery.)

Paul Szabo - pszmaths.usyd.edu.au http://www.maths.usyd.edu.au:8000/u/psz/
School of Mathematics and Statistics University of Sydney 2006 Australia

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