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Re: perlsec question

by hawson (Monk)
on Dec 14, 2001 at 02:57 UTC ( #131814=note: print w/replies, xml ) Need Help??


in reply to perlsec question

They all deal with shells, and executing external commands. If you are 100% sure that you do not execute any external commands at all, then you don't need to worry about them. This means that your code can't have any system or exec, but you should also be wary of open, and (I think) syscall.
  • $IFS is the "Internal Field Seperator" used between fields on a command line. For example, if you set IFS="/", then /usr/bin/ls becomes "usr bin ls". This happens before the shell looks for the command in the path, so if someone can place a command called "usr" in the path, that will be executed instead of what you intended.
  • CDPATH is to the 'cd' command as $PATH is to executing a command. An example:
    [jbecker@deadlands /]$ echo $CDPATH /home/jbecker [jbecker@deadlands /]$ pwd / [jbecker@deadlands /]$ file /home/jbecker/pilot /home/jbecker/pilot/: directory [jbecker@deadlands /]$ cd pilot /home/jbecker/pilot [jbecker@deadlands pilot]$ pwd /home/jbecker/pilot
    This could be bad if you use relative directories within your code and execute things within them. I expect this is more of a shell programming issue, but it can bite you with perl as well.
  • $ENV usually is the full path to a file that gets executed by certain shells (MKS Korn shell at least) before it (the shell) does anything else. This could easily be used to create a setuid root shell if something is tricked into running a shell as root that, in turn, executes the $ENV file.
  • $BASH_ENV: from the bash man page:
    When bash is started non-interactively, to run a shell script, +for example, it looks for the variable BASH_ENV in the environment, expands its value + if it appears there, and uses the expanded value as the name of a file to read and e +xecute. Bash behaves as if the following command were executed: if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi but the value of the PATH variable is not used to search for th +e file name.
    It's the same, essentially, as ENV. Icky.

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