Re: [vox-tech] php security (was: another php question)

[Samuel Merritt <snmerritt@ucdaviMAPSs.edu>]

On Thu, Jun 06, 2002 at 02:12:25PM -0700, Tim Riley wrote:
> 
> 
> Matt Roper wrote:
> 
> > With this solution, what keeps people from using something like
> > "../../../etc/shadow" as $arg?  You'd probably need to strip out slashes
> > and ..'s to be safe...
> >
> > Matt
> >
> 
> Good thinking Matt and Jeff. How about
> 
> $file2open = ( substr( $arg[ 1 ], 0, 1 ) == "." )
>                 ? ""
>                 : $APPLICATION_HOME_DIRECTORY . $arg[ 1 ];
> 
> This checks the first character for a dot by using the substring function
> inside
> the ternary operator. If someone tries to penetrate your system, file2open
> will fail.

That's not enough. What about foo/../../../etc/shadow ? 

A real solution, in my mind, is to break up the path using / (or its 
HTML-encoded equivalent, %2f) as a divider, to get a list of directories 
to traverse. Then, traverse directories one by one down the list, and when 
you reach the filename, check to see if you're above 
$APPLICATION_HOME_DIRECTORY. 

Alternately, if you don't have files in multiple directories, just check 
the given filename for slashes. If any are found, give an error; else, 
feed them the file. 

Yet another way (I'm on a roll tonight) is to have a table in your 
function, mapping (say)

1 => "/home/me/cars/mustang.dat"
2 => "/home/me/cars/camaro.dat"
... etc. 

Then, just access /path/to/script.php?file=N to get a file displayed, and 
look up N in your table, and display the appropriate file or give an 
error. 

> >
> > On Thu, Jun 06, 2002 at 12:20:31PM -0700, Tim Riley wrote:
> > > An easy way around exposing /etc/anything is to do what Apache does with
> > > HTML documents: only reference documents inside a relative directory.
> > >
> > > e.g., $file2open = $APPLICATION_HOME_DIRECTORY . $arg[ 1 ]
> > >

-- 
Samuel Merritt
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