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Full Discussion: Safely parsing parameters
Top Forums Shell Programming and Scripting Safely parsing parameters Post 302405346 by drewk on Thursday 18th of March 2010 03:07:47 PM
Old 03-18-2010
If you you run your parameters through awk or perl, you can also break them apart if you do not want to use eval.

Code:
perl -nle 'BEGIN {map {print} @ARGV; exit;}' root=/dev/sda3 noacpi foo "Baz mumble" `echo muahahahaha >&2`
muahahahaha
root=/dev/sda3
noacpi
foo
Baz mumble

Note that the backticks you used in your example are being executed prior to being fed to the perl script. Whatever the user can execute using backticks on your command line, he would have the privileges to execute directly before he executed your script.

The security "hole" only exists if you elevate privileges in your script and then have a way to execute arbitrary code, no?

If you are still concerned, perl or awk can split arbitrary strings just like the shell inside of the interpreter, but this is not entirely trivial.

You would just need to decide which expansions you would want to support and which not:

Shell Expansions - Bash Reference Manual
 

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MUMBLE-SERVER-CLI(1)						   User Commands					      MUMBLE-SERVER-CLI(1)

NAME
mumble-server-cli - allows calling methods of mumble-server from the shell SYNOPSIS
mumble-server-cli [options] [<method name>] [<method arguments>] DESCRIPTION
Each method argument has the form: [<data type: bool|int|float|string>:]value If you do not specify a data type, string will be assumed, otherwise `value' will be converted to the given type first. The bool conversion interprets each of 'True', 'true', '1', 'Yes', 'yes' as True, everything else as False. Example: int:4 float:3.5 string:oh:hai foobar bool:yes OPTIONS
-h, --help show this help message and exit -d DJANGO_SETTINGS, --django-settings=DJANGO_SETTINGS if specified, get connstring and slice defaults from the given Django settings module. Default: empty. -c CONNSTRING, --connstring=CONNSTRING connection string to use. Default is 'Meta:tcp -h 127.0.0.1 -p 6502'. -s SLICE, --slice=SLICE path to the slice file. Default is '/usr/share/slice/Murmur.ice'. -e ENCODING, --encoding=ENCODING Character set arguments are encoded in. Default: Read from LANG env variable with fallback to UTF-8. -v, --verbose Show verbose messages on stderr SEE ALSO
The full documentation for mumble-server-cli is maintained as a Texinfo manual. If the info and mumble-server-cli programs are properly installed at your site, the command info mumble-server-cli should give you access to the complete manual. AUTHOR
Mumble-Django and mumble-server-cli have been written by Michael Ziegler <diese-addy@funzt-halt.net>. mumble-server-cli February 2010 MUMBLE-SERVER-CLI(1)
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