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Special Forums Cybersecurity Attacking Potential of sh-scripts Post 302508899 by Perderabo on Tuesday 29th of March 2011 11:23:47 AM
Old 03-29-2011
If simply reading files needs to be prevented you are going to be out of luck with your approach. With bash or ksh a user with no access to any executables can do stuff like:
Code:
function cat { while read l ; do echo "$l" ; done < $1 ; }
function ls { while [ $# -ne 0 ] ; do echo "$1" ; shift; done ;}

and browse the system for any readable files. You really need to put users in a chroot jail and ensure that they have no root access to get true security.
 

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BZEXE(1)						      General Commands Manual							  BZEXE(1)

NAME
bzexe - compress executable files in place SYNOPSIS
bzexe [ name ... ] DESCRIPTION
The bzexe utility allows you to compress executables in place and have them automatically uncompress and execute when you run them (at a penalty in performance). For example if you execute ``bzexe /bin/cat'' it will create the following two files: -r-xr-xr-x 1 root bin 9644 Feb 11 11:16 /bin/cat -r-xr-xr-x 1 bin bin 24576 Nov 23 13:21 /bin/cat~ /bin/cat~ is the original file and /bin/cat is the self-uncompressing executable file. You can remove /bin/cat~ once you are sure that /bin/cat works properly. This utility is most useful on systems with very small disks. OPTIONS
-d Decompress the given executables instead of compressing them. SEE ALSO
bzip2(1), znew(1), zmore(1), zcmp(1), zforce(1) CAVEATS
The compressed executable is a shell script. This may create some security holes. In particular, the compressed executable relies on the PATH environment variable to find gzip and some other utilities (tail, chmod, ln, sleep). BUGS
bzexe attempts to retain the original file attributes on the compressed executable, but you may have to fix them manually in some cases, using chmod or chown. BZEXE(1)
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