[vox-tech] Need help securing a simple perl CGI

[Matt Roper]

I think someone can still access files outside your WWW directory by
requesting a file called .\./somefile.  When your script first checks
for instances of ".." in the URL, it doesn't find any since the periods
are separated by a backslash.  The script then removes all backslashes,
changing the URL to ../somefile.


Matt


On Sun, Feb 17, 2002 at 10:26:28PM -0800, Ryan wrote:
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> This is a perl cgi script I wrote to allow me to have large html files on my 
> web host without exceeding my storage quota.
> 
> I'd like it looked at, _I_ can no longer abuse it to run random commands or 
> go where I shouldn't, but that doesn't mean others can'.
> 
> Any other feedback would also be great.
> 
> #!/usr/bin/perl
> #Let users transparently access files that are gzipped server-side
> #Useful only to keep under my storage quota ;-)
> 
> my $in = $ENV{'QUERY_STRING'};		# Handle CGI calls
> $in =~ s/\+/ /g;			# Replace '+' with ' '
> $in =~ s/%(..)/pack("c",hex($1))/ge;	# Undo URL quoting
> 
> $in =~ s/\.\.//g;			# Foil Nasty h4x0rz trying to desend
> 					# directories
> $in =~ s/\\//g;				# There is no need for backslashes!
> $in =~ s/\'//g;				# prevent h4x0rz from
> 					# running commands like
> 					# zcat.cgi?file=foo.html.gz';rm -rf *'
> 
> my %data = split (/=/, $in);		# Make an array
> 
> my $file = $data{'file'};		# get the name of the requested file
> 
> print "Content-Type: text/html\n\n";
> # print `echo '$file'`;			# debugging
> print `zcat ~/WWW/'$file'`;		# quotes prevent nastys.
> 
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* Matt Roper <matt@mattrope.com>                *
* http://www.mattrope.com                       *
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